Research Collection. Doctoral Thesis. ETH Library. Author(s): Bieler, Peter. Publication Date: 1992

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1 Reserch Collection Doctorl Thesis Agronomic nd physiologicl spects of postflowering drought tolernce of perl millet (Pennisetum glucum (L.) R.Br.) in the Shel Author(s): Bieler, Peter Publiction Dte: 1992 Permnent Link: Rights / License: In Copyright - Non-Commercil Use Permitted This pge ws generted utomticlly upon downlod from the ETH Zurich Reserch Collection. For more informtion plese consult the Terms of use. ETH Librry

2 Diss. ETH No AGRONOMIC AND PHYSIOLOGICAL ASPECTS OF POSTFLOWERING DROUGHT TOLERANCE OF PEARL MILLET (PENNISETUM GLAUCUM (L.) R.Br.) IN THE SAHEL A disserttion submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of Doctor of Nturl Sciences presented by PETER BIELER Dipl. Ing. Agr, ETH Zurich (Switzerlnd) born Mrch 7, 1963 citizen of Solothurn (SO) ccepted on the recommendtion of Prof.Dr.P.Stmp, exminer Prof.DrJ.J.Oeilli, co-exminer Zurich, 1992

3 L'etrnger ne voit que ce qu'il sit. Proverbe fncin

4 Shelin Contents 1. Summry 1 Resume 3 2. ICRISAT - Center 6 3. Generl Introduction Drought Stress in Generl Drought Stress in Perl Millet Postflowering Drought Stress Screening in West Afric Introduction Mterils nd Methods Loction nd Soil Chrcteristics Plnt Mteril Experimentl Design nd Irrigtion Tretments Crop Tretments Observtions nd Mesurements Sttisticl Anlysis Results Discussion Grin Growth Under Postflowering Drought Stress Introduction Mterils nd Methods Experimentl Design nd Crop Mngement Observtions Dt Anlysis Results Grin Growth Under Well-Wtered Conditions nd Drought Stress Grin Growth nd Drought Response Discussion Crbohydrtes Reserves During Postflowering Drought Stress Introduction Mterils nd Methods Experimentl Design Smpling nd Processing of Plnt Prts Chemicl Anlysis of Nonstructurl Crbohydrtes Results Yield nd Yield Relted Prmeters in the Yield Plot Totl Nonstructurl Crbohydrtes Crbohydrtes Under Unlimited Versus Limited Tillering 6.4. Discussion 62

5 7. Further Aspects of Plnt Development After Flowering Introduction Mterils nd Methods Experimentl Design Vegettive Growth Observtions Root Growth Observtions Neutron Probe Mesurements Results Vegettive nd Genertive Development, nd Yield Perfor mnce Root Growth Neutron Probe Results Discussion Generl Discussion nd Conclusion References 89 Annex I 97 Annex II 99 Annex III 12 Annex IV 13 Acknowledgement Curriculum Vite

6 Tble of Abbrevitions DAS dys fter sowing DRI drought response index EF erly flowering FL time to flowering GFP grin filling period GGR grin growth rte ICRISAT Interntionl Crop Reserch Institute for the Semi-Arid Tropics ISC ICRISAT Shelin Centre LAI LF LGGP LP M SAT TNC lef re index lte flowering liner grin growth phse lg phse mturity semi-rid tropics totl nonstructurl crbohydrtes

7 1 1. Summry Perl millet (Pennisetum glucum (L.) R.Br.) s the most importnt crop in Shelin subsistence frming fces vrious biotic nd biotic production constrints. One of the most cited nd lso most fered is postflowering drought stress, due to the irregulr inter- nd intr-sesonl rinfll pttern in the region. Grin filling hs been previously described s being the most sensitive stge to drought stress in perl millet. For this reson it is necessry to include postflo wering drought tolernce in new vrieties being developed in lrge scle breeding progrms. Therefore relible screening technique hs to be developed. A first step is to describe the effect of drought stress, nd to chrcterize millet genotypes for their drought response, nd to look for genotypic differences in vrious gronomic nd physiologicl prmeters which re probbly importnt for drought tolernce. Vrious ttempts hve been reported in the literture. An pproch to identify prmeters responsible for positive drought response (drought tolernce) by multiple regression to enble clssifiction of genotypes for their individul drought response is suggested. Three hot off-seson trils on the experimentl site of the Shelin Center of the Interntionl Crop Reserch Institute for the Semi-Arid Tropics (ICRISAT) in Sdore (Niger, West Afric) were crried out including lrge number of millet genotypes of West Africn origin. Grin yield under drought stress ws reduced by lmost 5% compred to the irrigted control. Correltion nlysis suggested individul pnicle grin yield under postflowering drought conditions s vible prmeter for selection of drought tolernt genotypes. Inconsistency of the drought response over the three yers dt could be reduced in simple stbility nlysis. Individul pnicle yield s determined by grin number nd grin size ws further investigted. In grin growth study lrge number of millet genotypes were exmined, for their grin filling chrcteristics under optimum conditions; nd for their rection under postflowering drought stress. It could be shown tht the rte of dry mtter ccumultion in grins under drought stress remined unchnged.

8 2 However the grin filling period ws significntly reduced, resulting in smller grin size. Additionlly grin bortion fter flowering reduced grin number per pnicle under drought stress. The physiology of contrsting genotypes ws studied for possible genotypic differences in the ssimilte supply responsible for grin filling. Therefore, wter soluble crbohydrtes were nlyzed in three genotypes under well-irrigted nd under postflowering drought stress conditions. 75% to 1% of the totl dry mtter ccumultion of the whole plnt fter nthesis ws explined by dry mtter increse in the pnicle. The three genotypes with different drought response showed no differences in crbohydrte supply under well-irrigted conditions. No chnge in crbohydrte reserves occurred from before nthesis until the end of grin filling. Therefore most ssimiltes for grin filling cme from current photosynthesis. Under drought stress the bilities to mintin photosynthesis nd to mobilize stored crbohy drtes were importnt to mintin grin filling. Genotypic differences in prtitioning crbohydrtes were identified but could not be dequtely explined with the vilble informtion. Further spects of plnt growth under drought stress were compred to the performnce under well-irrigted conditions. Tillers were found to contribute 33 % to totl grin yield under well-irrigted control nd 21 % only under drought stress conditions. Synchroniztion of flowering in tiller pnicles nd in the min stem pnicle ws importnt for grin yield under postflowering drought stress. Rooting pttern t flowering, nd the utiliztion of soil wter fter nthesis did not give precise ide of genotypic behvior due to environmentl vribility. The wilting point of perl millet ws between 6% nd 7% volumetric wter content in the sndy soils of the reserch sttion. Although postflowering drought tolernce of perl millet could not be quntified in this study it ws found tht n eventul screening of genotypes hs necessrily to be done in drought nursery. Individul pnicle grin yield s selection criteri together with stbility nlysis provides bsis for future breeding. However, the physiologicl mechnisms of grin filling, prticulrly influenced by the photoperiod sensitivity of dry mtter prtitioning, needs to be further investigted for perl millet.

9 3 Resume Le mil (Pennisetum glucum (L.) R.Br.), l plus importnte culture dns I'griculture de subsistnce u Shel, rencontre diverses contrintes l production de nture biotique et biotique. Une des plus citees et des plus crintes est l secheresse post-florle due I'irregulrite des pluies, entre les sisons et u sein des sisons. Le stde du remplissge des grins dej ete decrit comme le plus sensible l secheresse dns le cycle de developpement du mil. On done relise l necessite d'inclure l resistnce l secheresse post-florle dns progrmmes de selection. Une technique sure de criblge doit done etre mise u point. Une premiere demrche consiste decrire les effets de l secheresse et clsser des genotypes de mil, selon leur rection l secheresse, et de decrire des prmetres gronomique et physiologique responsble des rections des genotypes differents. Differents essis ont ete decrits dns l litterture. Une demrche visnt identifier les prmetres permettnt une rection positive l secheresse (resistnce) ete fite prtir des regressions multiple; elle conduit clsser des genotypes selon leurs rections specifiques l secheresse. Trois essis en sison-seche chude sur le site experimentl du centre shelien de I'lnstitut Interntionl de Recherche sur les Cultures des Zones Tropicles Semi-Arides (ICRISAT) Sdore (Niger, Afrique de I'Ouest) ont ete menes vec un grnd nombre de genotypes de mil provennt de I'Afrique de I'Ouest. Le rendement en grins, dns des conditions de secheresse, diminue de presque 5% comprtivement ux temoins. Une nlyse.de correltion montre que le rendement en grins pr pnicule individuelle dns des conditions de secheresse de post-florison peut servir de prmetre pour selectionner des genotypes resistnts l secheresse. Les problemes de vrition de l rection l secheresse pourrient etre expliques trvers une nlyse de stbilite simple prtir des donnees sur trois ns. Des recherches plus poussees ont ete fites sur le rendement pr pnicule en fonction du nombre des grins et de leur msse. En suivnt 1'evolution ponderle

10 4 des grins, on pu crcteriser un grnd nombre de genotypes de mil dns leurs modlites de remplissge des grins sous des conditions sub-optimles insi que dns leurs rections l secheresse post-florle. II ete decouvert que le tux d'ccumultion de mtiere seche dns les grins demeure inchnge dns des conditions de secheresse. Cependnt l duree de remplissge des grins est notoirement reduite vec pour consequence, des grins moins gros. De plus, en cs de secheresse, I'vortement des grins pres l florison en reduit le nombre. Le contexte physiologique ete etudie pour deceler d'eventuelles differences u niveu des genotypes pour l devolution des photosynthtes lors du remplissge des grins. Ceci mene nlyser les hydrtes de crbone solubles pour trois genotypes dns des conditions d'irrigtion et de secheresse post-florison. L'ccumultion totle de mtiere seche de l plnte entiere, pres I'nthese, etit due pour 75 1% ('ugmenttion de l mtiere seche du fit du developpement des pnicules. Trois genotypes choisis en fonction de leurs rections differentes l secheresse n'ont ps montre de differences pour ce qui est de l devolution des hydrtes de crbone, dns de tres bonnes conditions d'irrigtion. L quntite des reserves d'hydrtes de crbone vnt I'nthese n' ps vrie pendnt le remplissge des grins. Done, l pluprt des ssimilts jount un role dns le remplissge des grins proviendrient de l photosynthese cournte. Les cpcites mintenir l photosynthese sous conditions de secheresse et de mobiliser les hydrtes de crbone ccumules sont importntes pour ssurer le remplissge des grins et pour que le grin puisse concurrencer d'utres fcteurs comme l respirtion. Des differences ont ete decelees u niveu des genotypes dns leurs cpcites de reprtition des hydrtes de crbone, mis n'ont ps pu etre expliquees de mniere ppropriee, vec les informtions disponibles. D'utres spects de l croissnce de l plnte sous des conditions de secheres se, ont ete exmines et compres l sitution dns des conditions d'irrigtion. II ete constte que les tlles contribuient pour 33% u rendement totl en grins dns des conditions sub-optimles et pour 21% seulement dns des conditions de secheresse. L simultneity de florison entre les pnicules des tlles et celles de l tige pnnciple est importnte pour le rendement en grins dns des conditions de secheresse. L'exmen du systeme rcinire l florison

11 5 et ('observtion de I'utilistion de I'eu pres I'nthese n'ont ps donne une idee precise du comportement des genotypes en reltion vec I'environnement. Le point de fletrissement pour le mil se situe entre 6 7% de contenu en eu volumetrique dns les sols sblonneux de l sttion de recherche. Bien que l resistnce du mil l secheresse post-florle n'it ps pu etre quntifiee dns ces trvux de recherche, ceux-ci ont permis de degger l necessite de mener un criblge de genotypes dns une pepiniere sous conditions de secheresse. Le rendement en grins pr pnicule individuelle comme critere de selection insi qu'une nlyse de stbilite constitueront une bse pour l selection dns le future. Cependnt les mecnismes physiologiques du remplissge des grins sous influence notmment de l photosensibilite et de l reprtition de l mtiere seche, doivent fire I'objet de recherches plus vncees.

12 Shelin 6 2. ICRISAT Center The present studies were crried out t the ICRISAT (Interntionl Crop Reserch Institute for Semi-Arid Tropics) Shelin Center (ISC) in Niger, West Afric. The experimentl site is situted t Sdore t 13 15'N nd 2 18'E in the southwest of Niger ner the town of Sy, 45 km south of the cpitl Nimey nd 6 km west of the river Niger. The re included by the Center is 5 h, hlf of which is currently cultivted. ISC is situted on plteu t bout 24 m elevtion with slight north-south slope. As frequently found in the semi-rid tropics (SAT) the soils in this re re yellowish-colored sndy soils, often shllow, with low fertility nd low orgnic mtter (see lso 4.2.1). The four months riny seson from June to September is chrcterized with n verge rinfll of 561 mm (Nimey) in the form of irregulr convective storms. The rest of the yer (October through My) is dry, often with dry winds bering dust from the north nd est (clled 'Hrmttn'). Tempertures re wrm ll yer with n verge of 29 C. Dytime mxim of up to 44 C occur during Mrch, April nd My, while two periods re chrcterized by lower dytime mxim, one of 32 C in August nd second of 34 C in December nd Jnury. ISC lies in the shelo-sudnin (35-6 mm nnul rinfll) climtic zone, semi-rid re chrcterized by vegettion of grsses, thorny bushes nd few trees. More thn 9 % of the popultion re involved in subsistence griculture. The primry food crop is perl millet (Pennisetum glucum (L.) R.Br.) often intercropped with cowpe (Vign unguicult L). Groundnuts (Archis hypoge) re grown s csh crop minly in the southern prt of the country. Pstorl grzing of sheep, gots nd cttle is the other mjor griculturl brnch. Almost ll field work is done by hnd lbor. Animl trction is rre, mechnicl trction prcticlly not existing.

13 7 The institute's objectives re (1) to serve s world center for the improvement of grin yield nd qulity of ICRISATs mndte crops grown in West Afric including: perl millet, sorghum, groundnut, chickpe nd pigeonpe; (2) to develop improved frming systems; (3) to identify constrints to griculturl production in the semi-rid tropics (SAT); nd (4) to ssist the development nd trnsfer of technology s well s trining. All of them include intensive bsic reserch including the collbortion of the Ntionl Reserch Progrms.

14 Generl Introduction Perl millet (Pennisetum glucum (L.) R.Br.) origintes from Afric with secondry center of vrietl diversifiction in Asi (Rchie nd Mjmudr 198). It is tillering C4-plnt, m tll. The inflorescence is dense spike up to 8 cm long. Millet is grown in res with rinfll of mm, nd hs better growth thn sorghum {Sorghum bicolor{l.) Moench) under dry conditions. It hs lrge rnge of genetic diversity in grin yield in West Afric. Grin yield rnges between 2 nd 12 kg/h depending on rinfll conditions. The grin is of excellent qulity in terms of nutrition with protein content of 11-19% (Kumr 1989). Perl millet is the predominnt cerel of the drought-prone Shelin zone of West Afric. Forty-nine percent of the world's cultivted re with perl millet is locted in West Afric (12.2 Mio h in 1986, FAO production yerbook), minly in Burkin Fso, Chd, Mli, Niger, Nigeri nd Senegl. It is the primry food crop nd the bsis of subsistence frming in these countries. The Shel hs very low griculturl potentil (Snders 1989). Wter conserv tion nd incresing soil fertility re perceived to be the two principl wys to improve this sitution. ISC (ICRISAT Shelin Centre) scientists estimte constrints to millet production s drought (3%), soil fertility (2%), Strig (prsite weed, 2%), bird ttck (15%), insect pests (1%) nd diseses (5%) (dt not published). Perl millet in the SAT (Semi Arid Tropics) fces high growing seson tempertures nd very frequently errtic rinfll resulting in high inter- nd intr-sesonl vrition of mount nd durtion of rinfll (Sivkumr 1986, 1989). Annul rinfll in this zone (3-6mm) hs been persistently below verge since the lte 196s (Forest 1982; Sivkumr 1989b). More importntly, rinfll during August when the soil profile normlly fills, storing wter for the grin filling period of the crop during September/October, hs declined by s much s 4% in some loctions (Sivkumr 1989b). Consequent ly, perl millet grown in the Shelin zone is now frequently subjected to drought

15 9 during grin filling. Therefore cropping systems nd crop cultivrs tht re cpble of coping with this vrition, together with high development plsticity of the crop re required Drought Stress in Generl The observed yield in crop is the expression of its genetic yield potentil in given environment. Effects of drought stress re mostly expressed in terms of yield reduction, the extent of which is tken s n expression of drought susceptibility. Screening progrms hve often tried to tret drought resistnce s one single spect. However breeding for drought resistnce hs been reported to be extremely difficult (O'Neill et l. 1987; Sgr et t. 1984) since response to drought is generlly combintion of vrious physiologicl nd gronomic expressions. Therefore keen interest still exists to find n gronomic prmeter tht covers crucil responses to drought, nd might be helpful s selection tool. A plnt generlly responds to drought s constrint by invoking in one of the following mjor ccepted mechnisms (Ugherughe 1987; Annerose 1988; Jones er/. 1981): drought escpe Erliness, controlled by the time of flowering, is one of two importnt drought escpe mechnisms. The plnt reches mturity before drought stress ffects its genertive development nd therefore escpes from the effects of lte drought. Erliness however is negtively correlted to yield in yers with dequte rinfll. Time to flowering determines the length of the growing period nd is controlled by one or two genes only (App Ro et l. 1988). Photoperiodic sensitivity controls the length of the developmentl cycle of genotype nd so the time to flowering. Drought escpe is often nd esily exploited in breeding progrms s it cn dd to yield consistency but is often used under the misleding nme of drought 'resistnce'.

16 1 A second drought escpe mechnism concerns developmentl plsticity in phenology during mid-seson stress. The plnt mkes up for the yield loss of the min culm with n incresed tiller number or tiller yield, produced fter the drought stress period. Such drought escpe mechnisms cn be included in breeding progrms in 'voiding' possible hrmful effects of dry periods during sensitive developmentl stges. drought voidnce Drought voidnce is bsed on voiding tissue dehydrtion by mintennce of high tissue wter potentils. This cn be chieved due to restricted wter loss (e.g., stomtl control; reduction in the mount of rdition bsorbed through lef movements; chnge in evportive surfce re through reduced lef re) or better wter supply by n extensive root system (e.g., increse root:shoot rtio). drought tolernce The third mechnism is drought tolernce nd is expressed in the mintennce of turgor pressure t low tissue wter potentils. This includes mechnisms s osmotic djustment, which is n ccumultion of solutes in plnt cells. This however is dependent on the rte of which stress is imposed nd is not pprently possible in ll physiologicl stges. It is therefore not only dependent on species or vrieties. Further drought tolernce includes protoplsmtic resistnce tht llows dehydrtion of plnt cells to ir humidity. However drought tolernce hs come to describe rnge of physiologicl expressions to wter deficit. In the following studies the term 'drought tolernce' is often used in generl sense, since the term 'resistnce' for n biotic constrint cnnot be quntified nd does not seem pproprite. In the literture prcticl pproches for the description of drought response voiding lbor intensive physiologicl mesurements included the rtio of yield under stress to yield potentil (yield under optimum conditions) of genotype, or the clcultion of threshold vlue with the verge yield of number of genotypes to describe stress index (Bruckner nd Frohberg 1987). Yield djustment using correction fctor per dy dvnce in flowering ws used to

17 11 clculte drought susceptibility index for whet, which ws consistent cross experiments (Fischer nd Murer 1978). Brley (Blum 1989), whet (Fischer nd Murer 1978) nd millet (Bidinger et l. 1987) grin yield under drought hd highly significnt cultivr differences showing wide rnge of individul drought response nd therefore wide selection potentil Drought Stress in Perl Millet Generlly, drought stress ffects plnt development dependent on time nd intensity of wter deficit s demonstrted for spring whet by Oertli (1988). Mhlkshmi nd Bidinger (1985) found tht wter deficit during pnicle development of perl millet reduced grin yield of the min stem pnicle, but could increse grin yield of tillers. Seemingly stress during the development of the min stem pnicle (mid-seson stress) is the reson for n incresed yield of the lter developing tiller pnicles; this wy tillers cn develop grin number comprble to the min shoot (Mhlkshmi nd Bidinger 1986; Mhlkshmi et l. 1987). The loss of grin yield due to mid-seson stress ws therefore compensted by chnging tiller performnce nd resulted in no difference in finl crop yield. Compenstion of yield due to tillers ws chieved by both n increse in tiller number nd grin number per tiller pnicle. For terminl (postflowering) stress this compenstion did not occur (Mhlkshmi nd Bidinger 1986). Growth nd yield components of millet fter mid-seson drought were further described by Mhlkshmi nd Bidinger (1985b). An importnt fctor ws the stge of the crop's development expressed s dys to pnicle initition nd dys to flowering. Dely in pnicle initition of min stems due to mid-seson drought resulted in more leves, tillers, lef re nd biomss. Grin yield ws not ffected (since compensted by tillers) thus the hrvest index ws reduced. Stress fter flowering decreses both min stem yield nd tiller yield which mkes postflowering drought the most sensitive stge of millet development. Mhlkshmi ef l. (1988) found tht millet grin yields were linerly reduced by

18 12 terminl (postflowering) stress with incresing intensity of stress. Yield reduction dependent on time of onset of stress in reltion to time to flowering (yield intensity), ws lower for grin number nd grin size the lter the stress occurred. Advnce in time of onset of stress by one dy cused.9% reduction in reltive grin yield. This shows the importnce of the timing of stress reltive to phenology for genotypes of different mturity groups plnted in sme tril. Bidinger et l. (1987) reported tht reduction in grin yield fter postflow ering stress cn rech up to 5% in perl millet. A significnt correltion between reltive yield under stress nd the time to flowering ws observed. This fct indictes the possibility of drought escpe. Bidinger et l. (1987) found tht yield potentil nd time to flowering ccount for more thn 5% of the totl vrition in millet grin yield under stress. Little reserch hs been crried out to understnd the mechnisms of drought tolernce in perl millet. The purpose of the present investigtions ws to test breeding strtegy including drought tolernce s criterion. Therefore n esily mesured prmeter with high genotypic vribility hd to be identified tht llows breeder to select lrge number of genotype entries. Furthermore, gronomic nd physiologicl spects should be investigted tht re responsible for the expression of the chosen prmeter. The presented results come from field experiments including West Africn perl millet genotypes. Since most of the genetic mteril is rther heterogeneous, sophisticted physiologicl mesure ments re probbly very difficult to interpret. Therefore the min purpose ws to increse the knowledge bout morphologicl growth chrcters under controlled well-wtered conditions compred to postflowering drought stress conditions nd to mke use of the informtion for description of drought tolernce.

19 13 4. Postflowering Drought Stress Screening in West Afric 4.1. Introduction It is highly desirble to include postflowering drought tolernce into new vrieties being developed by breeding progrm of perl millet. However before this cn be strted it is necessry to estblish tht there is genetic vrition in response to drought nd lso to find relible mens of identifying plnts which hve the desired ttributes. This necessittes the vilbility of vible screening technique. Specific gronomic prmeters hve to be identified to select genotypes in breeding progrm. Postflowering drought tolernce is phenotypic expression of interctions of mny prmeters in stress environments. Using mostly millet lines of Indin origin Bidinger et l. (1987) proved the required lrge selection potentil for breeding process. By withholding irrigtion from the time of 5% flowering of 5% of the vrieties, they were ble to show vrietl differences in grin yield of perl millet. However, such differences were found to be result of the combintion of yield potentil (yield under well-wtered conditions), time to flowering nd defined genotype specific drought response (Bidinger ef l. 1987b). They developed n nlyticl technique to clculte drought response index (DRI) from the residul of this multiple regression for ech genotype. The reltionships of the DRI to gronomic prmeters suggested some of them s vible to be used in postflowering drought-screens. The experiments described in this chpter were undertken to test for West Afric the postflowering drought screening method nd nlysis developed by Bidinger et l. (1987b), using mterils exclusively of West Africn origin. Further more, consistency of drought response of individul genotypes s well s the stbility of the defined screening prmeter re discussed.

20 Mterils nd Methods Loction nd Soil Chrcteristics Three field experiments were conducted t the ICRISAT Shelin Center (ISC) during the hot dry sesons (Februry-My) in 1988, 1989 nd 199. The period is rinfree nd chrcterized with high men ir tempertures (3-32 C) nd high potentil evportion rtes (6-15 mm) (see Annex I for detiled informtion). The trils were crried out on yellowish lomy snd soil of more thn 3 m depth. ISC's soils belong to the Alfisols (Lbucheri series fter West er/. 1984), chrcterized by % snd, 4.7 % silt, % cly nd n verge ph of 4.9. The lterite occurs t 2-4 m depth. The wter content in the soil t field cpcity to 1 m depth is 12 mm. Typicl bsic chemicl nlysis for ph nd P of the fields re provided by the tril 199 with soil smples tken t hrvest (Tble 4.1). After the recommendtions of Btiono etl. (1991) phosphorous ws vilble in excess. The verge of ISC's soils hve 123 mg N kg"1 soil nd 39.1 mg K kg"1. The trils were plnted on the sme field without ny cover crop following ny rottion pln. Tble 4.1. Chemicl soil properties, Sdore Depth (cm) ph (H2) P(ppm)(Bry 1) Plnt Mteril A totl of 42 (1988) nd 45 (1989 nd 199) genotypes were plnted in the trils. They included dvnced breeding lines, relesed vrieties nd lndrces from Burkin Fso, Mli, Niger, Nigeri nd Senegl (Annex II). Due to high disese incidence (e.g., downy mildew on the dwrf types), bird ttck nd extremes in

21 15 flowering dte, only 34 genotypes in 1988 nd 1989 nd 32 genotypes in 199 were included in the finl nlysis. The rnge of flowering of these genotypes did not exceed 1 dys. This intervl ws considered to be the likely mximum rnge in flowering mong breeding mterils intended for specific climtic zone. The entry composition of the three experiments vried between yers. Six genotypes were consistent in ll three experiments (Tble 4.2). Tble 4.2. Common genotypes ot the trils in 1988, 1989 nd 199. Genotype ICMVIS ICMVIS HKP SYNTH-1 CIVT P3Kok3 Origin ISC ISC INRAN1 Mli INRAN INRAN Experimentl Design nd Irrigtion Tretments The experimentl design ws modified split-plot, with min plots irrigtion tretments replicted thrice nd sub-plots genotypes replicted twice within ech min plot. Loction of min-plots vried between yers, excluding ny error due to residul soil-wter in the field. Sub-plots consisted in 4 rows of 5 m length,.75 m prt. Irrigtion tretments consisted of well irrigted control (compen sting ctul evpotrnspirtion) nd postflowering drought stress. Both tretments received regulr irrigtion on 4 to 7 dy cycle depending on the stge of development of the crop. The mount of wter pplied per inigtion ws clculted by summing up the pn evportion of the number of dys preceding (crop coefficient ssumed to be unity). Irrigtion ws done by line-source 11nstitut Ntionl de Recherches Agronomiques du Niger

22 16 overhed sprinkler. Due to technicl problems in irrigtion, the 199 tril ws drought stressed just before flowering, ffecting both irrigtion tretments Crop Tretments Frmyrd mnure of ph (H2)=8 t the rte of 4 kg P h"1, 12 kg N h'1 nd 32 kg orgnic mtter nd minerl fertilizer t the rte of 45 kg N h'1, 19.6 kg P h"1 nd 37.4 kg K h"1 were brodcst prior to plnting nd incorported with trctor drwn cultivtor. A further dose of 26 kg of N h"1 ws pplied 18 dys fter sowing (DAS) nd incorported with donkey drwn plough. Crbofurn (Nemticide) ws pplied t the rte of 4 kg.i. h"1 t the time of sowing in 1988 nd 1989 only. Seeds were sown by mchine in 1988 nd 1989, nd by hnd in 199 on ridges nd thinned to three plnts per hill.4 m prt t DAS. The resultnt high plnt popultion of 1' plnts h"1 (trditionlly 3' plnts h"1) hstened soil wter depletion nd enhnced drought stress fter withholding irrigtion. Weeds were controlled both mechniclly (donkey-drwn cultivtor) nd mnully. Birdscring prt, no other disese or pest control ws required fter plnting Observtions nd Mesurements Only the middle two rows of 2.4 m length (3.6 m2) in 1988, 2. m (3. m2) in 1989 nd 2.8 m (4.2 m2) in 199 were hrvested t mturity (yield plot). The rest of the plots were utilized for other observtions resulting in different sizes of the yield plots between the three yers. Time to flowering ws determined on plot bsis when stigms hd emerged on 5% of ll min shoot inflorescences in the yield plot (Miti nd Bidinger 1981). The lst irrigtion for the stress tretment ws pplied three to four dys before the likely 5% flowering verge of the stress plots simulting n erly ending of the rins. At hrvest the number of pnicles, pnicle weight, grin yield nd bove-ground biomss were recorded per plot. All

23 17 crop nd grin smples were oven dried t 7 C for t lest 24 hours before weighing. Triplicte smples of 1 grins were tken rndomly from the bulk plot hrvest to determine the 1 grin weight. Number of grins per pnicle nd per unit re, pnicle yield, threshing percentge s the rtio of grin yield to totl pnicle mss s well s the hrvest index were derived from the dt Sttisticl nlysis The method developed t the ICRISAT Center in Hyderbd, Indi (Bidinger et l. 1987b) ws used to clssify millet genotypes ccording to Drought Response Index (DRI). This method is bsed on the ssumption tht the grin yield of genotype under drought stress conditions (YJ is function of potentil yield under irrigted conditions (YpJ, time to flowering (FL,) nd drought response (DR,): = Y + by,, + cfl, + DR, + E, (1) where E is rndom error with zero men nd vrince o. Bidinger et l. (1987b) found tht bout hlf of the vrition under stress could be ttributed to vrition in potentil yield nd time to flowering. The prmeters,b nd c of eqution (1) cn therefore be estimted by minimizing the residuls (DR, + E). Yield under stress cn then be estimted s: rm = + b\ + cfl, (2) The difference between the ctul nd estimted yields is then equl to the residuls (remining terms of eqution (1)): = (Y-Yg DR, + E. (3) A test of significnce of the drought response (DR,) cn be clculted s: z- ly.-rj/o- (4)

24 18 where o is the stndrd error of Y' (eqution (2)). A threshold vlue for Z is selected to be 1.3, selecting those genotypes in the upper nd lower 1% of the norml distribution of Ys. If Z is < 1.3, DR, is considered to be zero. This mens tht the bsolute vlue of the difference between the mesured yield under stress (YJ nd the predicted yield (Y'J ws less thn 1.3 times the stndrd error of Y'. In this cse genotype is considered to hve no drought response (DR^O). The bove derived estimtes of E nd re ffected by those cses where DR, *. Therefore, better estimte of E (E') nd of o (o') cn be clculted using only those genotypes for which Z < 1.3, i.e., for which DR,= : Y" = + byp, + cfl, +E' (5) DR, cn then be expressed by substituting E' in (3), where E' is estimted by o'. The drought response index (DRI) is bsed on DR nd is defined s follows: (')if Y -Y'J < o', then DRI, = (ii) if Y. Y-. > ', then DRI, - = (Ys Y'J/' DR, is, thereby, expressed s multiple of o' nd my hve positive or negtive vlue. Genotypes with positive DRI hve positive drought response (tolernt to postflowering drought stress), genotypes with negtive DRI re susceptible nd genotypes with DRI of zero re verge in response to drought stress. The DRI s clculted here is independent of both yield potentil nd time to flowering. The DRI for ll genotypes were correlted to yield components in the control nd drought stress tretment to identify prmeters relted to drought response. Mesured nd clculted yield prmeters in both irrigtion tretments were further correlted cross genotype mens to grin yield under stress to exmine ssocitions between the prmeters. Reltions of yield under stress with prmeters mesured in the well-irrigted tretment were ssumed to be independent of the stress effects (constitutive), while ssocitions with prme ters only under stress were ssumed to reflect the response of the genotype to stress (dptive). These dptive prmeters were correlted to both time to

25 19 flowering nd to DRI to seprte those reltionships due to drought escpe (correlted to time to flowering) from those expressing drought response (correlted to DRI). A stbility nlysis for the six common genotypes in ll three experiments ws crried out for the determinnts of DRI nd lso for the dptive yield prmeters showing promising correltions to DRI. The method pplied ws developed by Eberhrt nd Russel (1966). They used the following model to study the stbility of prmeter of T vrieties under's' different environments: = Y m + B,l, +5, (i=1,2,...t;j=1,2,...s) where = Y,, Men of the prmeter of i'h vriety in jlh environment, m Men of the prmeter of ll the vrieties = over ll the environments, B, The regression coefficient of the i,h vriety = on the environ mentl index tht mesures the response of this vriety to vrying environments, = I, The environmentl index. It is defined s the devition of the men of ll the vrieties t given loction from the overll men with the sum of ll = I,. = 8, devition from regression of the im vriety t the jlh environ ment. Two prmeters of stbility re clculted: ) The regression coefficient, which is the regression of the performnce of ech vriety under different environments on the environmentl mens of the prmeter over ll the genotypes nd is estimted s follows: B, = sum Y.J/suml2. This stbility prmeter ws lso described nd used by Finly nd Wilkinson (1963).

26 2 b) The men squre devitions (s2d) from the liner regression which represents the unexplinble devitions from the regression on the environmentl index. A vriety is sid to be stble, if the regression coefficient is one (b=1) nd the devition not significntly different from zero (s2d =). Finly nd Wilkinson described trit s below verge stbility for b>1 resulting in lrge chnges in the trit due to smll environmentl influences. For b<1 the genotype is defined to hve bove verge stbility with bove verge vlues of the trit in poor environments, but possibly low vlues in better environments. For b=1 they spek of generl dptbility with bove verge of the trit, nd poorly dpted with below verge vlues of the trit. For sttisticl nlysis s ANOVA, correltion, liner nd multiple regression, MS DOS Computer with the Genstt 5, Relese 1.3 (by Lwes Agriculturl Trust, Rothmsted Experimentl Sttion, 1988) pckge ws used Results Substntil genotypic vribility for yield-relted trits under controlled wellirrigted conditions (control), ws observed s significnt F rtios from the nlysis of vrince for genotypes. This vribility ws mintined under postflowering drought stress. The brod rnges of grin yields under stress show the individul bility of genotypes to produce grins under drought stress nd proves wide potentil of genotypic expression tht cn be exploited in breeding progrm (Tble 4.3). The verge time to flowering ws significntly reduced in 1988 nd 1989 under drought stress, which must be due to n ccelerted development of lte flowering heds. The number of pnicles per m2 ws significntly reduced under drought stress. This indictes tht probbly the lter tillers did not chieve the flowering stge or did not produce ny grins. Grin yield under drought stress

27 21 Tble 4.3. Mens nd F rtios of genotypes for growth nd yield components mesured in the irrigted control (c) nd drought stress (s) tretments Sdore Vrible Mens F rtio Mens F rtio Mens F rtio Time to flowenng (dys) c " " " s " " " Biomss (g m2) c " " " s " " " Stover (g m2) c " " " s ' " " Pnicle (g m2) c " " s " " Grin yield (g m2) c " ' s " " Pnicle No m2 c ' " ' s " ' Pnicle yield (g) c " " " s 98 3 " " No grins pnicle' c " " " s " " Grin mss (g 1') c " " " s " " " No grins m2(* 13) c " " s " " Hrvest Index c " " " s " " 2 65 Threshing Percentge c " " " s " " ** P< 1 * P< 5 F rtios for irrigtion re significnt t 1% level for ll prmeters except in 199 for time to flowenng (5%) nd for stover dry weight, pnicle yield, grin number per pnicle, hrvest index nd threshing percentge (not significnt)

28 22 ws significntly (P<.1) reduced by 47% in 1988, 48% in 1989 nd 23% in 199 (Tble 4.3). The reltive reduction of grin yield under drought stress compred to grin yield under control, ws significntly correlted (P<.5) to grin yield under control in 1988 (r=.38) but not in 1989 (r=-.5) nor in 199 (r=.25). The yield loss ws due to reduced individul pnicle yield tht gin ws due to both reduced grin number nd reduced individul grin mss per pnicle. This resulted in lower threshing percentge (rtio pnicle dry weight to pnicle grin weight). Due to technicl problems, the control tretment in the 199 tril hd n unstisfctory irrigtion level resulting in slight wter stress. Therefore the reltive impct of the drought stress ws not s high s in the other yers. The reduction of the totl bove-ground biomss under drought stress ws primrily due to the reduced pnicle weight (Tble 4.3). The reduction of stover dry weight of 2-25% showing reduced plnt growth under drought stress fter flowering ws less thn for pnicle weight (between 24 nd 4%). The hrvest index declined between 13% nd 27% s result of the reduced grin yield. Correltion nlysis of yield under drought stress to prmeters in the control nd in the drought stress tretment were consistent over yers (Tble 4.4). Time to flowering, hrvest index nd threshing percentge were found to be constitutive trits nd therefore less dependent on stress, s grin yield under drought stress ws significntly correlted to these prmeters in the control. Totl boveground biomss nd stover dry weight in prticulr were not relted to grin yield under stress neither in the control nor the drought stress tretment. Other prmeters e.g., pnicle dry weight, pnicle yield, grin number per pnicle nd except in 1989 grin number per re, turned out to hve high response to stress nd re therefore predominntly dptive prmeters. The correltion of pnicle yield under drought stress to grin yield under drought tress ws one of the strongest correltions over three yers nd is shown in Figure 4.1.

29 23 Tble 4.4. Correltions of grin yield mesured under drought stress versus yield prmeters in the irrigted control nd drought stress tretments Sdore Correltion Coefficients Yield (stress) vs meter (control) pr- Yield (stress) vs ter (stress) prme Time to Flowering (dys) - 59" - 48" - 36' - 46" - 35' - 28 Biomss (g m2) Stover (g m2) - 41' Pnicle (g m2) ' 32 94' 96" 72" Pnicle No m " 46" Pnicle yield (g) " 86" No grins pnicle' ' 61" 84" Grin mss (g 1') No grins m2(x13) ' 24 79' 85' 96" Hrvest Index 64' ' 69" 93" Threshing % 43' 5" 33 81' 8' 78" " P< 1 * P< 5 Individul DRI vlues vned from less thn -1 8 to more thn +2 1 (Annex II) Of the 1 genotypes nlyzed twenty showed positive vlue (tolernt drought response) nd 28 genotypes hd negtive DRI (susceptible drought response). The remining genotypes hd DRI of, indicting n verge drought response For ltter, genotypes grin yield under drought stress could be dequtely estimted with yield potentil nd time to flowenng Under drought stress grm yield, pnicle yield, grm number per pnicle nd per re (ll dptive prmeters) showed the strongest reltionships to DRI These correltions were consistent for ll three yers (Tble 4 5) A number of prmeters significntly relted to DRI were t the sme time expressions of drought escpe e g relted to time to, flowering (Tble 4 5) Biomss nd stover

30 r Pnicle yield (g) l 2 b) ** t * *# 5 c * %. **** * * ** # * ** * % Grin yield (g m-2) Figure 4.1. Correltions of grin yield m'2 to pnicle yield (both under drought stress) of genotype verges in 1988 (), 1989 (b) nd 199 (c). Sdore

31 Tble 4.5. Correltions of yield prmeters in the drought stress tretment to time to flowering under drought stress ncfdri Sdore Correltion Coefficients Time to flowering (dys) Biomss (g m2) 53' 47" 56' 56' 59" 2 Stover (gm2) 76" 63" 77" 26 37" 6 Pnicle (g m2) ' 73" 74" 31 Grin yield (g m2) - 46' " 83" Pnicle No m2-55' - 47" - 66' Pnicle yield (g) ' 78" 88" No grins pnicle' ' 63' 92" Grin mss (g) - 47' - 57" ' - 1 No grins m2 (x13) " 85" Hrvest Index - 74" - 69' " Threshing % " " 44 91" P< 1 * P< 5 dry weight s indifferent, hrvest index nd threshing percentge s rther constitutive, nd number of pnicles m"2 nd to lesser extent individul grin mss s rther dptive prmeters were ll correlted to time to flowenng (within the drought stress tretment) nd lso to DRI Selecting genotypes fter one of these prmeters would probbly identify rther erly ones Grin yield ws significntly relted to flowenng in 1988 nd 1989 only As per definition DRI ws not relted to time to flowenng in ll three yers The prmeters pnicle yield, grin number pnicle1 nd to some extent grin number m2 under drought stress were found to be the best expressions of individul genotype's drought response No reltionship of ny of the yield ttnbutes in the control tretment to DRI ws significnt, therefore dt re not presented

32 26 In Figure 4.2 the correltion of pnicle grin yield to DRI is shown. The six common genotypes of ll three yers re indicted by numbers. It cn be seen tht lthough overll results of the correltion nlysis were very consistent over ll three trils (yers), the comprison of the individul drought responses of the six genotypes common to ll trils indicted high interction between genotypes nd yers (Tble 4.6 nd Annex II). Tble 4.6. Drought Response Indexes (DRI) of the six common genotypes. Sdore No. Genotype ICMVIS ICMVIS HKP SYNTH CIVT P3 KOLO -.5 In n ttempt to improve comprbility of the three yers, the flowering dte ws expressed s growing degree dys (bse temperture 1 C, optimum temper ture 33 C nd mximum temperture 45 C; see 5.2.3) nd DRI ws reclculted. This however did not improve the consistency of DRI (dt not presented). A stbility nlysis ws therefore required to investigte the genotype x yer interction s well s the consistency of the three determinnts of DRI (time to flowering, potentil grin yield, nd grin yield under stress) s well s the recommended prmeter pnicle yield under drought stress. The other prmeters grin number per pnicle nd per unit re re not further nlyzed, since their utiliztion s selection prmeter is too lbor intensive in lrge screenings nd for grin number per re not very vible.

33 27 Drought Response Index (DRI) 4 o d2 g BOB 3 Effi-CEJ S B-B 3D 8 o b) D 1 BIBB B-Q fh rwn gg- c B BB B8 1-CBD Pnicle yield (g) Figure 4.2. Reltionship of pnicle yield under drought stress to drought response index (DRI) in 1988 (), 1989 (b) nd 199 (c). The verticl line representing the tril verge. Numbers indicting common genotypes between yers (see Tble 4.6). Sdore

34 * 28 The nlysis of vrince of the prmeters pnicle grin yield, time to flowering, grin yield under control nd drought stress of the six common genotypes ws clculted over the three yers (Tble 4.7). Time to flowering, pnicle yield under drought stress nd grin yield under drought stress ll showed high genotypic vribility. Further pnicle yield nd grin yield under drought stress hd high genotype x yer interction confirming the high vribility nd different expression of these prmeters of ech genotype in the different climtic environment of the three yers. Grin yield under well-irrigted conditions (potentil yield) ws not vrible between genotypes. Tble 4.7. Men squres of ANOVA for pnicle yield (stress), time to flowering, grin yield (control) nd grin yield (stress) over three yers for six genotypes. Sdore Source of Vrition d.f. Pnicle yield (stress) Flowering Grin yield (control) Grin yield (stress) genotype " 82.7" " yer " 44.7" " 265" genotypexyer ' " Residul Totl 17 * P<.5 ** P<.1 Tble 4.8. Stbility prmeters (b=regression coefficient [shded]; s\=men squre devition from regression) of pnicle yield (stress), time to flowering, grin yield (control) nd grin yield (stress) of the six common genotypes. Sdore Pnicle yield (stress) Flowering Grin yield (control) Grin yield (stress) Genotype b s2, b s2 b s2 b s2d ICMVIS ICMVIS s%$?,, >' 4.25 ;j>.3^v".89 {''it > * :Q;to : 2.6 \P$f%ii 1-46 :-$Mr 416 '-',9? t1 349 HKP "llf;* *^ 1-47 Qte', '$$$? so tfm: ifj S 153 SYNTH-1 t).s$*".36 'jjssri 1.46 :1,16,273 f j ^ 288 CIVT %m/^: 1.66 tm % 2.55 tm 466 * ; f ;? 589 P3KOLO %m>;: 2.64 'fj2 *",= 1.28,97, imilf4f 36

35 29 The results of the stbility nlysis of the four prmeters including the two stbility prmeters re shown for genotypes in Tble 4.8. After the method suggested by Eberhrt nd Russell (1966) none of the six genotypes chieved the required conditions of b=1 nd s2,j=u for stble genotypes' expression in ny of the prmeters. According to Finly nd Wilkinson (1963) however, grin yield under well-irrigted conditions is stble for ll genotypes with regression coefficient of bout one. Time to flowering nd grin yield under drought stress re very unstble between environments. The stbility of genotype ws different between these prmeters. For pnicle yield under drought stress the genotypes ICMVIS 85332, SYNTH-1, nd P3Kolo showed bove verge stbility while ICMVIS 85321, HKP, nd CIVT showed below verge stbility Discussion Drought stress during grin filling of perl millet reduced grin yield substntilly. This ws minly due to reduced grin numbers per pnicle nd to n inferior individul grin mss resulting in low pnicle yield. This grees with the findings of Bidinger et l. (1987) with mteril of lrgely Indin origin. A reduced kernel number per pnicle under postflowering drought stress ws lso reported for mize (Grnt et l. 1989). These findings suggest tht under drought stress the grin filling phse ws reduced, shortening the ssimilte supply to the grins nd resulting in smller grin mss due to erly senescence s ws suggested in sorghum (Duncn et l. 1981). The reduced grin number per pnicle ws pprently due to selective grin bortion fter flowering s result of the drought stress. In mize this is reported to be sequence of physiologicl events rther thn restricted ssimilte supply to the grin (Reed nd Singletry, 1989). The lck of significnt correltions of the reltive yield reduction under drought stress to grin yield under control indictes tht high potentil yield does not men better drought response. The reltionship of yield components to grin yield under drought stress were different between tretments, but consistent over yers. This proves different pttern of yield structure under drought stress thn

36 3 under control. Therefore no prmeter mesured under well-irrigted conditions cn be used to estimte grin yield under postflowering drought, confirming the necessity of drought nurseries to select for drought tolernce. Seprting yield prmeters into groups of predominntly drought escpe (relted to flowering), or drought tolernce (relted to DRI) helped to identify prmeters with potentil s screening tools for drought tolernce. Both grin number per pnicle nd pnicle yield were identified s prmeters relted to drought tolernce nd therefore re suggested to be used s possible screening prmeters. However, to determine grin number of ech individul pnicle is lbor intensive tsk nd is not fesible. Therefore pnicle yield seems the most likely prmeter. Similr reltionships were found by Bidinger etl. (1987b) for Indin millet. Prt of the results of 1988 nd 1989 were published in Fussell ef l. (1991) where the phenotype-yield reltionships nd the breeding spect is further discussed. By selecting entries bsed on pnicle yield under drought stress conditions lrge proportion of drought tolernt genotypes could be identified (positive drought response). Genotypes with pnicle yield higher thn the tril's men show either n indifferent rection to drought or hve positive response (Figure 4.2). Overll results nd reltionships of yield relted prmeters were constnt between yers. This confirms DRI s vible tool nd suggests the method of nlysis for the identifiction of selection prmeter using inter-reltionships of DRI s fesible. However the individul DRI vried for the six common genotypes between yers. A stbility nlysis of the determinnts of DRI identified grin yield under well-irrigted conditions (potentil yield) s prmeter consistent for ll genotypes. However time to flowering, determining genotype's cycle length is very unstble for most genotypes. Due to this, s well s to the experimentl design required by the irrigtion fcilities, the genotypes were submitted to drought stress in different physiologicl stges cross the three yers nd therefore performed vrible. Modelling of individul genotypes is therefore not fesible with the suggested method, since time to flowering is of high importnce in drought prone environments nd hs to be predictble.

37 31 The use of pnicle yield s screening prmeter for postflowering drought tolernce is hzrdous since significnt genotype x yer interction ws found. The genotypes ICMVIS 85332, Synth-1, nd P3Kolo with regression coefficient (b) of < 1 fter the stbility nlysis for pnicle yield suggested by Finly nd Wilkinson (1963) re clssified s insensitive to environmentl chnges. These genotypes cn be expected to hve mostly positive drought response nd to perform well under postflowering drought stress. The other three genotypes (ICMVIS 85321, HKP, nd CIVT) with regression coefficients > 1 re probbly very sensitive to environmentl chnges. They definitely cnnot be recommended for drought-prone res. The results indicte tht stbility nlysis is necessry complement to the screening with n gronomic prmeter. The high genotype x yer interction of pnicle yield mkes this pproch of screening-technique unrelible nd requires lrge mount of dt over yers nd/or loctions to get resonble stbility nlysis. Since genotype cn be relibly chrcterized by its yield potentil, further reserch hs to improve the experimentl design using improved irrigtion fcilities nd lso to emphsize on photoperiodic sensitivity of individul genotypes to stbilize their cycle length. Further physiologicl prmeter explining the genotype x yer interction of pnicle yield, expressing t the sme time genotypic vribility, could identify drought tolernt genotypes on more vible bsis s it is suggested so fr.

38 32 5. Grin Growth under Postflowering Drought Stress 5.1. Introduction Reduced grin yields from postflowering drought stress were primrily due to both reduced grin numbers per pnicle nd individul grin mss (Fussell et l. 1991; see lso 4.4.). The reduced grin number per pnicle ws due to selective bortion of grins tht occurred fter flowering due to drought stress. Vrition in individul grin mss, in response to drought stress during the grin filling period (GFP), cn be due either to reduction in grin growth rte (GGR) nd/or length of GFP. The processes of grin growth nd the role of these grin growth prmeters in the response of perl millet to drought hve not been elucidted in the literture. There exists genetic vrition in perl millet for single grin mss (Burton nd Powell 1968), which vries from 3.5 to 16. mg grin"1 (Rchie nd Mjmudr 198). Fussell nd Person (1978) identified two phses of the grin filling period in perl millet: n initil short lg phse (LP) when little dry weight ccumultion tkes plce nd presumbly cell differentition occurs, nd subsequent liner grin growth phse (LGGP). They found tht differences in both the length of the grin filling period nd the grin growth rte (GGR) in the LGGP were correlted with grin mss differences between perl millet genotypes. Phenotypic differences for these prmeters were found to be primrily genetic rther thn environmentl in rice (Oryz stiv L.) (Jones ef l. 1979) nd whet (Triticum estivum L) (Bruckner nd Frohberg 1987b), suggesting tht these prmeters could be used in selection progrm, if this ws wrrnted. For whet Bruckner nd Frohberg (1987b) proposed tht high GGR with reltively short durtion ws desirble, risk reducing strtegy for postflowering drought stress. The extent of genotypic differences in individul grin growth of perl millet in well-wtered nd postflowering drought stress conditions is exmined in this

39 33 chpter. Further the reltionships of grin growth prmeters to yield nd yield components under well-wtered nd drought stress conditions re studied, in order to understnd their importnce in yield determintion. Their reltion to drought tolernce is investigted Mterils nd Methods Experimentl Design nd Crop Mngement Detiled descriptions of the trils in both 1988 nd 1989 re fully given in chpter 4. The split-plot design consisted of min plots (irrigtion tretment) replicted thrice nd subplots (genotypes) replicted twice within ech min plot. Inigtion tretments were well-irrigted control nd postflowering drought stress where irrigtion ws completely discontinued t 5% flowering of 5% of the plots. Forty-five millet genotypes were included in both field trils but forty-two nd forty-one genotypes were included in the nlysis in 1988 nd 1989, respectively, ccepting higher vrition of differences in flowering dte of genotype thn in the nlysis done in chpter 4. The genotypes excluded from the nlysis were dwrf types nd those very susceptible to downy mildew. Sets of genotypes vried between yers Observtions Flowering for individul plots ws determined s the dte when 5% of the stigms hd emerged on 5% of ll the inflorescences in the plot (Miti nd Bidinger 1981). Individul inflorescences of both min stems nd tillers were tgged on their dte of flowering. The inflorescences were grouped for monitoring of grin growth bsed on men time to flowering of plot. The first group (erly flowering: EF) consisted of inflorescences flowering before the men flowering time of the plot nd the second group (lte flowering: LF) of inflorescences

40 34 flowering fter this time. This seprtion ws undertken to observe ny differences of grin growth chrcters for erly nd lte inflorescences within genotype under both well-wtered (control) nd drought stress environments without differentiting between min stem nd tiller inflorescences. Smplings were stggered cross the replictions, such tht one smple ws tken per genotype nd tretment from ech repliction groups 1 to 3 nd 4 to 6 for ech dy resulting in set of dt with two replictions. For both erly nd lte flowering inflorescences, smples of t lest 1 grins were tken midwy long one inflorescence dily from dy 5 to dy 19 fter the pnicles were tgged in the control nd from dy 5 to dy 16 in the stress tretment in In 1989, dily smpling ws reduced (dy 6 to dy 17 in the control nd dy 6 to dy 14 in the stress tretment). These smpling periods were ssumed to cover the liner grin growth phse (LGGP) in ech tretment. Further, totl of 18 smples per genotype nd repliction group (6 pnicles per repliction) were tken rndomly t 25 dys fter flowering (i.e., mturity, Miti nd Bidinger 1981) in ech tretment to determine finl grin mss fter the end of grin filling. Inflorescences were smpled once only. Grin smples were oven-dried for 24h t 7 C, hnd-threshed, counted nd their 1-grin mss determined Dt nlysis The grin growth nd development ws bsed on therml time. The use of therml time ws necessry for line comprisons s durtion of perl millet grin development is determined primrily by temperture (Fussell et l. 198; Ong 1983) nd there were vritions in temperture between nd within the sesons. For tempertures below the optimum for grin growth, therml time (,) ws clculted s: e1= s civr,,) 1=1

41 LP). 35 where T, is men temperture for the ith dy nd Tb is the bse temperture below which grin growth is zero. For supr-optiml tempertures, therml time (2) ws clculted s: " hi (r.-r,) (t-t ) (T--r<>> where Tm is the mximum temperture bove which grin growth is cesed nd T is the optimum temperture for grin growth. Therml time cn be ccumult ed s C dy using the two equtions. It ws clculted using Tb of 1 C (Ong 1983), T of 33 C (Fussell et l. 198; Ong 1983) nd Tm of 45 C. Both T nd Tm hve not been ccurtely determined for grin development in perl millet. The crdinl tempertures used re supported by the findings for other development processes of the crop (Grci-Huidobro ef l. 1982; Ong nd Monteith 1985) nd the observtion tht Tb is nerly constnt for rnge of developmentl processes in t lest one line of perl millet (Ong nd Monteith 1985) nd ws ssumed to be the sme for grin filling. Air tempertures used were recorded t the meteorologicl sttion t ISC, Sdore. Liner regressions were fitted to the grin smple dt tken during the liner grin growth phse (LGGP) to determine the grin growth rte (GGR) nd the length of the lg phse (LP) (fter the method of Johnson nd Tnner 1972) (Figure 5.1). The GGR ws expressed s microgrms per grin per C dy. LP ws derived by setting the regression of the LGGP to grin mss of zero, nd expressed s C dy from flowering. Durtion of GFP ws clculted by setting the regression to the finl grin mss determined from the mturity smple. LGGP ws derived s the period from the end of LP to end of GFP (i.e., GFP - For both irrigtion tretments, the smples from erly flowering (EF) nd lte flowering (LF) pnicles were initilly kept seprte nd their grin growth chrcteristics nlyzed. Finlly, the two smples were combined to clculte men genotype grin growth ttributes in both environments.

42 36 Reltionships between grin growth chrcteristics nd yield ttributes were determined using correltion nlysis. In ddition, their correltion to drought tolernce (the drought response index [DRI] s explined in 4.2) nd time to flowering ws clculted for the sub-sets of 34 lines nlyzed in both yers. Grin weight (mg/grin) (iriri Filling Period (GFP). Liner Grin Growth Phse. 9 Lg Phse* (LGGP) y Mturity (LP) slope Grin Growth Rte * Flowering / Therml time from flowering (*C d) Figure 5.1. Model of grin growth nlysis Results Grin Growth Under Well-Wtered Conditions nd Drought Stress There ws considerble genotypic vribility for the components of the durtion of grin filling (LP, LGGP, GFP), the grin growth rte (GGR) nd the finl grin mss under well-wtered conditions (control), in both yers. Tble 5.1 shows the mens of these prmeters over both smpling periods of the erly nd lte flowering inflorescences. The extent of genotypic vrition for grin growth prmeters observed under control ws mintined under postflowering drought

43 ' 37 stress (Tble 5 1) The length of grm filling period (GFP), liner grin growth phse (LGGP) nd the GGR vried nerly two-fold between lines in both yers, while the length of the lg phse (LP) vried up to three-fold. The overll rnge of C dy for GFP represents 13 to 22 dys (t men temperture of 3-32 C) There ws no significnt difference between the genotype mens for LGGP, GGR nd finl grm mss between the two yers. For the men finl grin mss of ll genotypes, there ws significnt vntion in 1988 only. In 1989, men LP nd GFP were slightly longer thn observed in 1988 Tble 5.1. Mens, rnges nd results of ANOVA for grin growth prmeters under wellwtered nd drought stress tretments Sdore 1988 nd well-wtered drought stressed Grm growth trit Men' Rnge Men Rnge F 2 CV% Lg phse ( C dy) Liner grin growth phse ( C dy) " 31 8 Grin filling period ( C dy) " 18 2 Grin growth rte (ug grin' ("Cdy)1) 28" " Finl grin mss (mg grm1) 7 1" " " well-wtered drought stressed Grin growth trit Men Rnge Men Rnge F, cv% Lg phse ( C dy) Liner grin growth phse ( C dy) " 314 Grin filling period ( C dy) 392" " 154 Grin growth rte (ug grin' ("Cdy)1) 26" " " 23 9 Finl grin mss (mg grin') 7 4" " " 13 3 P< 5 " P< 1 for genotypes '" nd for irrigtion

44 38 Totl GFP nd LGGP were significntly reduced by postflowering drought stress, when compred with well-wtered conditions (Tble 5.1). In both yers, verge GFP ws shortened by between C dy (i.e., more thn two dys) due to the imposed drought stress. Men GGR (ll genotypes) ws not ffected by drought stress in 1988 (compred to the control, Tble 5.1). However, in 1989 drought stress significntly (P<.1) reduced the men GGR by 15%. Nonethe less, only 3 of the 41 genotypes showed significntly (P<.5) lower GGR under drought stress in 1989, nd there ws only one such genotype in 1988 (dt not presented). In 1988 high GGR were positively (P<.5) ssocited with the erly flowering genotypes, which lso hd hevier grins. These trends, evident though not lwys significnt under control, were enhnced under postflowering drought stress. Averge finl grin mss got reduced by 21% in 1988 nd 28% in 1989 (Tble 5.1). The flowering distributions of smples of erly flowering (EF) nd lte flowering (LF) inflorescences re shown in Figure 5.2. The timing of flowering of single inflorescence in reltion to the distribution of flowering within genotype hd significnt influence on grin growth prmeters under control conditions only in 1989 (Tble 5.2). Grins of EF hd, on verge, longer lg phses (LP) (significnt with P<.1 only in 1989). The verge liner grin growth period (LGGP) for the erly flowering ws the sme s the lte flowering inflorescences in both yers. As result, the men grin filling period (GFP) for ll genotypes remined unchnged for the LF in 1988, but ws significntly shorter compred to EF in The grin growth rte (GGR), verged cross ll genotypes, ws not significntly different between smples of inflorescences from the first or second hlf of the flowering distribution. Under well-wtered conditions only 4 out of 42 genotypes in 1988 nd 3 out of 41 genotypes in 1989 hd significntly lower GGR for lte flowering inflorescences. However the finl mss of individul grins ws significntly reduced in the LF in both yers. Comprison of grin growth prmeters from erly (EF) nd lte (LF) flowering smples under postflowering drought stress to control showed higher reduction of ll prmeters in the LF thn in the EF (Tble 5.2), s expected. Under drought stress finl grin msses were reduced in the lter inflorescences minly

45 becuse of shorter LGGP. 12 Number of Pnicles SO Dys After Sowing (DAS) I Erly Flowering (EF) i Lte Flowering (LF) Figure 5.2. Flowering distribution of erly nd lte flowering smples s verges of two yers (1988 nd 1989) in control () nd drought stress (b). Sdore However, the men GGR (ll lines) ws not significntly different from EF nd LF with only 5 out of 42 genotypes in 1988, nd 8 out of 41 genotypes in 1989 hving lower GGR for inflorescences from the second hlf of the flowering distribution. The reltionships of grin growth prmeters to ech other nd to certin yield ttributes under well-wtered conditions were exmined using simple correltion nlysis cross genotype mens (Tble 5.3). The length of liner grin growth

46 o 1 P< " 5 P< * smples between Vrince F,= distribution, flowering the of hlf second LF = distribution, flowering the of hlf first = EF ' grin1) " " ' (mg mss grin Finl dy)') '( C grin (ug rte growth Grin dy) 9" " " ( C period filling Grin dy) ( C phse growth grin Liner 8" " ' dy) ( C phse Lg Men Men Men Men Men Men LF EF F. LF EF F, LF EF Men LF Men EF stressed drought well-wtered stressed drought well-wtered nd 1988 Sdor6 tretments stress drought nd well-wtered in distribution flowenng the of hlf second nd first the of inflorescences from prmeters growth grin of Mens 5.2. Tble

47 41 phse (LGGP) nd grin filling period (GFP) s well s the grin growth rte (GGR) were positively correlted with finl grin mss; genotypes with higher grin mss hd longer LGGP nd fster grin growth rte. Long LGGP were ssocited with short lg phse (LP) nd low GGR (the ltter only in 1989). Long LP therefore enhnced grin growth rte. Other yield ttributes thn finl grin mss, such s pnicle yield nd grin yield itself were unrelted or inconsistently relted cross yers to the grin growth prmeters. Severl interreltionships between grin growth prmeters nd finl grin mss found under control conditions were mintined under postflowering drought stress conditions (Tble 5.3) nd did not chnge nture nor intensity. Simple correltion nlysis confirmed the overll importnce of liner grin growth phse (LGGP) nd grin filling period (GFP) in determining finl grin mss. The vrition in genotypic response to drought stress ws relted to the time to flowering of genotype through the negtive ssocition of time to flowering with the lg phse (LP) (Tble 5.3). As one might expect finl grin mss ws significntly (P<.1) correlted to pnicle yield nd grin yield under drought stress. GFP ws consistently significntly correlted to grin yield per re nd pnicle yield under drought stress lthough this positive correltion ws not very high. Therefore GFP ws found predominntly dptive trit (see 4.2.6) since there ws no significnt correltion of GFP under control to yield under stress (dt not presented). Its reltionship to time to flowering however indictes the drought escpe chrcter of the prmeter. Other grin growth prmeters were mostly unrelted or inconsistently relted to these yield ttributes. In Tble 5.4 the verge grin growth prmeters of the six genotypes discussed in chpter 4 re listed. All prmeters seemed to be higher in 1989 thn in 1988 under controlled conditions. Except liner grin growth phse nd totl grin filling period in 1989, no genotypic differences in grin growth prmeters could be identified under controlled conditions. Under drought stress genotypic differences occurred in 1988 for totl liner grin filling period, grin growth rte nd finl grin mss, while no differences were detected in Genotypes' grin growth prmeters showed different responses to drought stress, but resulted ll in reduced finl grin mss. Genotypes showed either longer lg

48 tretment stressed S=drought control, C»well-wtered ' 1 P< " 5 P< ' dy) ( C phse Lg 76" - 55" - 53" - 58" dy) ( C phse growth grm Liner dy) ( C period filling Grin 49" " " - -43" 68" " 77' 57" 7" dy)1) ( C grm' (ng rte growth Grm 21 31' 57' 59" 33' 42" grin') 64" 63" 64" 61" 35" 45" 4" (mg mss grin Finl 52" 36' " 5" " " 26 78" 38' 53" 7 42" " -12 (g) yield Pnicle -38" ' - 31' " 67" (dy) 72" - 46" - 6" - -45" 35' " flowering to Time 5" " " " 71" 3 8" 44" 58" 22 42" m2) (g yield Grin S C S C S C S C S C S C grin') (g mss grin Finl dy)') ( C grm1 ug ( rte growth Grm dy) ( C period filling Grm dy) ( C phse growth grin Liner dy) ( C phse Lg DRI 1989 nd 1988 SdorS row) (second 1989 nd row) (first 1988 for DRI nd tretment) (S) stress drought nd (C) control the (in ttributes yield nd growth grm between Correltions 5.3. Tble

49 b b b b 1 24 b b b b b b b S C S C dy)"1 ( C grin1) (mg grin'1 (ug rte mss grin Finl growth Grin 79 be bc b b be bc be c be be b b b b S C S C dy) dy) ( C period ( C phse growth filling grin Totl grin Liner P3Kok> CIVT Synth HKP ICMVIS ICMVIS P3Kolo CIVT Synth HKP ICMVIS ICMVIS 1988 S C dy) ( C phse Lg p<.5. for test rnge multiple Duncn's fter genotypes grouping Letters control). % to in (reltive (S) stress drought under nd (rel) (C) control under genotypes six for prmeters growth grin of Mens 5.4. Tble

50 44 phses nd reduced liner grin growth phses or vice vers. The response ws not consistent between yers llowing ny identifiction of grin growth strtegy Grin Growth nd Drought Response To explore the role of grin growth prmeters in drought tolernce, correltion nlysis of grin growth prmeters mesured in both irrigtion tretments of subset of 34 lines (which flowered from 59 to 71 dys fter sowing) to DRI ws crried out for both yers (Tble 5.3). None of the grin growth prmeters nd finl grin mss under both well-wtered nd postflowering drought conditions were relted to drought response (i.e., to DRI). The reltionship between grin yield in stress nd GGR in 1988 (Tble 5.3) thus ppers to be n expression of drought escpe, consequence of the positive reltionships of both yield under postflowering drought stress nd GGR, with erly flowering. The sme ws found for GFP s the only consistent dptive prmeter. There were significnt reltionships between certin grin growth prmeters nd the chnges in GFP nd grin mss cused by postflowering drought stress. Tble 5.5 shows the correltions of differences in grin filling period (GFP), grin growth rte (GGR) nd grin mss under control nd drought stress. Genotypes with long GFP under control conditions hd significntly (P<.1) lrger reductions in GFP nd grin mss in the drought stress. Genotypes with high GGR under control conditions, however, were not more likely to hve lrger reductions in grin mss under drought stress. The extent of the reduction of GFP ws ssocited (r=.79 in 1988 nd r=.7 in 1989) with the reduction in grin mss, s expected.

51 45 Tble 5.5. Correltions between certin prmeters of grin growth nd the reltive reduction (%) of grin filling period, grin filling rte nd grin mss due to postflowering drought stress Sdore 1988 nd 1989 Reltive reduction in Yer Grin filling Grin growth Grin mss period rte Well-wtered conditions Grin filling period ( C dy) Grm growth rte (ug grin' ( C dy)') Grin mss (mg grin1) Drought stress conditions Grin filling period ( C dy) Grin growth rte (ug grin1 ( C dy)') Grm mss (mg grin') " ' ' " " ' " " - 59" 44" " " 32' -.43" 43" - 56" - 65" " " 11-72" * P< 5 " P< Discussion Perl millet is known to vry gretly in grin mss (Burton nd Powell 1968; Rchie nd Mjmudr 198). This study corrobortes these findings, with genetic mteril mostly of Shelin origin. The overll rnge of grin filling period (GFP) is consistent with previous studies (Bishnoi et l. 1985; Fussell nd Person 1978; Fussell etl. 198; Ong 1983) but much shorter thn reported for other cerels, i.e., whet, rye nd triticle (Stmp et l. 1982). The sigmoid grin growth curve s it ws used in the studies of Stmp etl. (1982) could therefore be reduced to liner model. Figure 5.3 shows the verge genotype grin

52 46 growth curves for ech yer nd tretment confirming the vibility of liner growth curve with the high R2 for the regression. Differences between genotypes in grin mss were mostly due to differences in length of liner grin growth phse (LGGP), nd to lesser extent to differences in grin growth rte (GGR), confirming the results with smller set of genotypes (Fussell nd Person 198). These differences were evident in the control but less so in the drought stress tretment. The mgnitude of the vritions in the vrious grin growth prmeters (more thn two-fold in both yers nd both moisture environments) ppers sufficient for effective utiliztion of grin growth prmeters in perl millet breeding progrm for ll environments. Qrin mss (mg/grin.) 8 R-Squres for liner fitting control stress '* z8* -d' -* Therml time from flowering ( C) * Control D Stress Figure 5.3. Grin growth curves under control nd drought stress in 1988 nd Sdore The principl effect of postflowering drought stress on individul grin growth ws to reduce grin mss. This occurred primrily through reduction in GFP rther thn GGR for lrge mjority of the lines tested (Figure 5.3). Similr findings hve been reported for mize (Ze mys L.) (Outtr et l. 1987). Trunction

53 47 of GFP could hve resulted from limited ssimilte supply or (nd) reduced grin storge cpcity. In mize, restricted current photosynthte production cused by wter deficit ws implicted s the reson for reduced grin mss under postflowering drought stress (Outtr et l. 1987b). Wter deficit during the lg phse (LP) could hve reduced the grin storge cpcity, determined by cell division during tht phse of grin development, s found in mize (Outtr etl. 1987). Becuse the length of LP ws little ffected by the drought stress imposed, restricted current ssimilte supply ppers more likely explntion for the reduced grin mss nd erly cesstion of grin filling thn decresed storge cpcity. The mintennce of GGR under drought stress implies tht perl millet possesses robust dpttion mechnisms to ensure seed production. Two sources of ssimilte supply re vilble to mintin grin filling: first, current photosynthte from photosynthetic ctivity fter flowering nd, secondly, trnsloction of stored crbohydrtes produced before flowering. Severe wter stress is known to cuse stomtl closure in perl millet (Squire 1979; Blck nd Squire 1979; Henson etl. 1981) nd, presumbly, reduction in photosynthte production (Boyer 1976). However, lck of current ssimiltion cn be buffered by mobiliztion of sugrs stored in the stems in mny cerel crops. Fussell etl. (198) nd Pnde ef l. (1983) observed tht soluble sugrs stored in stems prior to grin filling in peri millet were mobilized during grin filling. In mize, under wter deficit conditions, the ssimiltes stored before nthesis were estimted to contribute 26 to 3% of finl grin weight (Outtr et l. 1987b; Jurgens et l. 1978). Quntifiction of the contribution of stored stem sugrs to finl grin mss under either well-wtered or drought stressed conditions hs yet to be done for perl millet. Although the overll results of the two yers were consistent, the performnce of individul genotypes in their grin growth chrcteristics vried. This is ttributed minly due to the dte of onset of stress tht hd ffected individul genotypes in slightly different development stges since the beginning of drought stress could not be imposed for ech genotype individully. Consistent reltionships between grin yield under drought stress nd grin growth prmeters were found only for GFP nd grin mss. There re similr

54 48 reports for whet (Bruckner nd Frohberg 1987b; Syed nd Gdllh 1983). Furthermore, there were no consistent ssocitions between grin growth prmeters nd DRI, suggesting tht none of the grin growth prmeters mesured were expressions of drought tolernce or susceptibility. Therefore, selecting for grin growth prmeters to enhnce postflowering drought tolernce in perl millet ppers not to be fesible. However, exploiting certin drought escpe fetures observed for the grin growth prmeters does pper possible pproch to improving yield under postflowering drought stress. Lines with shorter GFP under well-wtered conditions hd smller reductions in both GFP nd grin mss under stress. Moreover, lines with higher GGR in well-wtered conditions hd smller reductions in GFP. Therefore, vible risk-reducing strtegy for res prone to postflowering stress would be to select lines with high GGR combined with reltively short GFP. Bruckner nd Frohberg (1987b) proposed similr pttern under postflowering drought stress in whet. Selecting for high GGR nd shorter GFP by direct mesurement in lrge number of perl millet lines my require too mny observtions nd not be cost effective.

55 6. Crbohydrtes Reserves During Postflowering Drought Stress Introduction Previous results indicted tht the reduced grin mss under postflowering drought stress conditions could hve been result of limited ssimilte supply. The contribution of different plnt prts to grin yield s well s the source of crbohydrtes for grin filling hve been thoroughly investigted, minly for the four mjor cerels: non-tillering C4-species sorghum (Goldsworthy 197) nd mize (Outtr et l. 1987) nd the tillering C3-species rice nd whet (Borrel et l. 1989). For perl millet Eghrevb (1981) found tht the flg lef hd only 5% of the totl ssimiltory surfce, but contributed to 32% of the totl grin dry mtter. He explined the high efficiency of the flg lef s reltive young plnt prt, its proximity to the sink nd the vntge position to intercept incoming rdition. Some studies report the effects of drought stress on mobiliztion nd trnsloc tion of ssimiltes, e.g., in mize (Outtr et l. 1987). In whet (Blum et l. 1983; McCig nd Clrke 1982) stem reserves of crbohydrtes re of high importnce for grin yield under drought stress. Westgte nd Boyer (1985) showed tht low lef wter potentil of mize s it occurs under drought stress, completely inhibited photosynthesis so tht reproductive development depended entirely on the reserves of ssimiltes. Dry mtter consisting minly in crbohy drtes, which hd ccumulted in mize stem nd leves were mobilized fter nthesis. The mount of stored ssimiltes before drought stress might therefore be importnt. In millet trnsloction of ssimiltes is dependent on temperture (Fussell ef l. 1978b nd 198). With incresing drought stress the contribution of lmost ll plnt prts decreses. However the contribution of the ssimiltes in millet stems increses s the contribution from leves decreses (Ro ef l. 1978). Long nd thick stems re therefore dvntgeous for storge of ssimiltes (Pnde ef l. 1983). Bidinger ef l. (1977) suggested tht the contribution of stored ssimiltes in whet of prenthesis photosynthesis cn

56 5 determine between 12% nd 98% of the grin yield under optimum conditions. Hume nd Cmpbell (1972) described n ccumultion of ssimiltes in com stlks until 2-3 weeks fter nthesis which then declined due to mobiliztion nd trnsloction into the grins. In plnts crbohydrtes cn be clssified in three ctegories (Vn Soest 1987): () simple sugrs nd their conjugtes ctive in intermediry plnt metbolism; (b) storge reserve compounds, e.g., strch, sucrose nd fructns; (c) structurl polyscchrides, e.g., pectines, hemicelluloses nd celluloses, which re generlly irretrievble to the plnts in times of stress. In the present study totl nonstructurl crbohydrtes (TNC) serving s storge nd energy reserves in plnt prts were nlyzed quntittively. Chnges in the mount of stored TNC from flowering up to mturity were investigted for the shoots of three genotypes. The effect of postflowering drought stress on the TNC content ws studied Mterils nd Methods Experimentl Design An off-seson tril ws estblished in The experimentl design ws splitplot with min-plots irrigtion tretments replicted twice nd sub-plots genotypes replicted five times within ech min plot. The irrigtion tretment consisted in well-wtered control nd postflowering drought stress tretment, where irrigtion ws withheld t 5% flowering (Miti et l. 1981) of 5% of the plots. Irrigtion ws done by liner moving overhed irrigtion system. Plots consisted in four rows of 5m length. Fertilizer ppliction nd crop tretments were the sme s in the tril of 199 (see 4.2.4). The tril ws plnted by hnd on ridges.75 m prt, in hills.25 m prt. Thinning ws done to one plnt per hill to enble the observtion of individul plnts. All plnts for the observtions were tken from the two middle rows.

57 sulfuric Smpling nd Processing of Plnt Prts Three millet genotypes (ICMVIS 85332, CIVT nd P3Kolo) were nlyzed for nonstructurl crbohydrtes. These genotypes hve similr phenology nd were expected to represent rnge of drought responses (see 4.3). Of the designed plnts for this study the min stems were tgged before tillering, excluding difficulties in differentiting min stems nd tillers in lter stge. The hills consisted in one plnt, with one min stem nd one tiller s ll other tillers hd been removed erly fter their ppernce in order to hve uniform smples. One genotype (CIVT) ws dditionlly left with ll its tillers s control. Plnts for yield nlysis were left to tiller normlly for ll genotypes. Flowering dte for min stem pnicles ws recorded. Smpling of plnts ws done t the stge of flowering (FL), t flowering + 9 dys (FL+9) nd t mturity (M) (blck-lyer stge) of plnt. One of the designed plnts per plot ws smpled t ech of the three dtes. The plnts were cut t ground level nd the totl plnt height of the min stem (including the pnicle) nd the dimeter of the stem t the bse of the pnicle ws mesured. The pnicle nd the tiller were dried s one smple ech. The min stem ws cut into three pieces equl of length including their corresponding leves. This resulted in five sub-smples per plnt nd smpling dte. Smples were tken between 8. h nd 9. h. All smples were dried immeditely fter hrvest t 6 C for 48 hours. Dry weight ws determined for ll smples before processing in hmmer mill nd subsequently in high speed mill to pss 1 mm sieve Chemicl Anlysis of Nonstructurl Crbohydrtes Totl wter-soluble nonstructurl crbohydrtes (TNC) were nlyzed quntit tively fter the method suggested for sorghum by Guirgossin et l. (1979). It consisted in colorimetric phenol - cid procedure determining TNC contents s hexose equivlents. Sugrs (including strch) were extrcted by boiling 25 mg of plnt smple in big test tubes, dding 15 ml of distilled wter during 4 minutes in wter bth. After cooling, 1 ml of ech cette buffer (ph

58 ), myloglucosidse (.5%), nd mylse (.25%) solutions were dded nd incubted for 24 hours t 6 C. It ws then filtered through Whtmn #42 pper into 1 ml volumetric flsks nd brought to volume. Enzyme blnks were included for ech run. One ml of qutic solution ws pipetted into test tubes nd 1 ml of phenol (5%) ws dded. Five ml of concentrted sulfuric cid were dded on test tube shker. The highly exothermic rection ws ccompnied by chnge to reddish color. Seven ml of distilled wter ws dded for dilution nd stirred gin. Redings were tken with spectrophotometer (Milton Roy, Spectronic 51) t 49 nm fter 3 minutes when the smples were cool nd the color fully developed. The nlysis of ech plnt smple ws repeted thrice. Glucose stndrds were used in concentrtions of.2,.4,.6,.8 nd 1 g/liter. TNC were clculted s % TNC s well s g TNC per plnt prt nd per plnt Results Yield nd Yield Relted Prmeters in the Yield Plot Some importnt prmeters for grin nd biomss s observed in the yield plot re presented in Tble 6.1 in order to bis the chemicl dt. Grin yield ws significntly reduced under drought stress of 42.4% for ICMVIS 85332,51.4% for CIVT but only of 25.1 % for P3Kolo. Flowering dte of plnt smples ws between 58 nd 6 dys fter sowing (DAS) nd did not differ significntly neither between smples of hrvests nor between genotypes. Therefore ll lines suffered drought stress during the sme physiologicl period. Stress plots received lst irrigtion t 62 DAS, equivlent to wter supply dequte for pproximtely four dys. This llowed sufficient wter supply to ll plnts during their period of cell differentition in the grin (lg phse). Compred to the two other genotypes the yield reduction ws miniml for P3Kolo. The reduction in biomss under drought stress ws significnt in ll three genotypes. This ws due to reduction of both stover dry weight nd pnicle dry weight. The decresed biomss under drought stress ws less in P3Kolo thn the other two genotypes.

59 ' 53 Tble 6.1. Yield prmeters of the yield plot. Sdore ICMVIS CIVT P3KolO Prmeter C S' C S C S CV% Flowering (dy) Biomss (g m'2) " " " 17 Stover (g m2) " " " 17 Pnicle (g m'2) ' " 39 31' 24 Grin yield (g m'2) ' " ' 34 Pnicle yield (g) " " " 26 1 C = well-irrigted control S = drought stressed P<.5 " P<.1 for irrigtion tretment Totl Nonstructurl Crbohydrtes Totl shoot biomss s derived from the totl dry weights of ll five plnt prts did not significntly differ between genotypes from the control from flowering to mturity (Figure 6.1). An verge of 35.5 % of the totl biomss t mturity ws produced during the grin filling phse. At hrvest the pnicle comprised 35.9 % of the totl biomss insted of 13.4 % t flowering. Therefore the mjor proportion of the increse of shoot dry weight ws in grin. All other plnt prts did not increse nor decrese dry weight significntly fter nthesis. From dt shown in Figure 6.1 the prtitioning coefficient ws clculted s the rtio between the ccumulted pnicle dry mtter from flowering to mturity to the totl dry mtter ccumulted by the plnt during the sme period. Prtitioning of dry mtter to the pnicle fter nthesis ws 1. for ICMVIS nd.74 for both CIVT nd P3Kolo. Tiller growth fter flowering ws nil nd hrdly ny tiller pnicles were produced, or filled. Plnt height ws not different between genotypes with finl height of 234 cm t flowering. Stem dimeter t the bse of the pnicle ws 8.8 mm t flowering for ll genotypes. Nine dys fter flowering the totl plnt dry weight s well s its distribution mong plnt prts under drought stress did not differ from the well-irrigted

60 54 dry weight (g) CIVT Figure 6.1. Distribution of dry weight in shoots of single plnts of three genotypes (ICMVIS (IC 32), CIVT nd P3Kolo) t flowering (), flowenng + 9 dys (b) nd mturity (c) under control (C) nd drought stress (S). Stndrd errors of mens re given in prenthesis. Sdore 1991.

61 55 conditions, indicting similr plnt growth during the erly grin filling (Figure 6.1). After this period dry weight ccumultion under drought stress ws nil nd totl dry weight even declined significntly in the cse of CIVT. In CIVT except for the pnicle the dry weight of ll plnt prts declined in the period of mid-grin filling to mturity. ICMVIS tended to increse its tiller weight. P3Kolo mintined dry weight in stem prts. A significnt reduction in dry weight occurred lso in the tillers of CIVT nd P3Kolo for the sme period. The prtitioning of dry mtter to the pnicle under drought stress ws for ll genotypes bove 1. (1.76 for ICMVIS 85332, 1.93 for CIVT nd 1.2 for P3Kolo). For this reson the ccumultion of dry mtter in the pnicle ws bove totl new dry mtter increse from flowering to mturity, compensted prtilly with trnsloction of dry mtter from dry mtter decresing stem prts nd vegettive plnt prts. The verge rte of dry weight ccumultion in the whole plnt from flowering to mturity got reduced to bout hlf compred to the well-irrigted tretment for ll genotypes. The pnicle weighed 12.4% of the totl bove-ground biomss t flowering nd 31.1% t mturity. At mturity the rtio of pnicle weight to stover weight remined the sme s in the well-wtered tretment. The concentrtion of totl nonstructurl crbohydrtes (%TNC) expressed s reltive contents showed significnt (P<.1) differences in plnt prts for ll hrvest dtes (Figure 6.2) in the control. As expected verge TNC contents per plnt incresed significntly from flowering to mturity: 11.5% t flowering, 13.9% nine dys lter nd 16.2% t mturity. This ws minly due to incresing TNC contents in the pnicle from 7.4% t flowering to 28.2% t mturity. No genotypic differences could be found under well-irrigted conditions. TNC contents in the stem prts did not chnge from flowering to mturity. The lower stem lwys hd higher level thn the middle stem, nd the ltter one higher thn the upper stem. Averge TNC content per plnt under drought stress incresed slightly from flowering (12.1 %) to FL+9 (13.1 %) nd decresed significntly t mturity (9.5%). Reltive TNC content declined for ll plnt prts except the pnicle from nthesis to mturity for ICMVIS nd CIVT. P3Kolo mintined its TNC levels in the stem prts up to FL+9 fter tht vlues declined for ll stem prts nd tillers

62 56 (Figure 6.2). The TNC content in the pnicle incresed significntly for ll genotypes from flowering to FL+9 nd ws then mintined (ICMVIS 85332), decresed (CIVT) or further incresed (P3Kolo). In tillers TNC content generlly declined significntly from FL+9 to mturity. Results similr to the reltive TNC content were found for the bsolute mount of TNC in the plnt prts in the control. Tble 6.2 shows totl TNC t the three physiologicl stges nd the reltive mount of TNC llocted in the pnicle. After nthesis TNC lmost exclusively incresed in the pnicle while in ll other plnt prts, including the tiller, chnges were not significnt (Figure 6.3). Only in P3Kolo n increse of stored TNC's took plce in the lower stem nd lso in the tiller in the second hlf of grin filling. The corresponding prtitioning coefficient of TNC fter nthesis to the pnicle ws of.97 for ICMVIS 85332,.81 for CIVT nd only.63 for P3Kolo in the period from flowering to mturity. Tble 6.2. Totl g TNC per plnt t three physiologicl stges (FL, FL+9, M) prenthesis Percentge of totl TNC prtitioned to pnicle Sdore 1991 In well-irrigted control drought stress Genotype FL FL+9 M FL FL+9 M ICMVIS (7 9) 164(4 9) 26 7(561) 13 6(71) 141(313) 13 3(59 8) CIVT 12 5(7 5) 213(31) 355(551) 16 4(91) 19 7(315) 1 (535) P3Kok> 13 6(6 7) 16 8(38 8) 371 (44 8) 12 9(7 6) 23 6(26 2) 2.1 (58 3) Corresponding to reltive TNC, totl TNC incresed from flowering to FL+9 nd then decresed to mturity under drought stress. ICMVIS showed stble mount of TNC in the plnt throughout grin filling (Tble 6.2). CIVT ccumulted TNC in the pnicle up to FL+9, fter tht vlues decresed in ll plnt prts except the pnicle which kept the sme content (Figure 6.3). P3Kolo incresed TNC in ll plnt prts between flowering nd FL+9, followed by drmtic decrese in ll stem prts nd tiller ccompnied by further ccumultion in the pnicle. Prtitioning of bsolute TNC to the pnicle from flowering to mturity ws

63 57 Figure 6.2. Concentrtion totl nonstructurl crbohydrtes (TNC) in shoots of single plnts of three genotypes (ICMVIS (IC 32), CIVT nd P3Kolo) t flowenng (), flowering + 9 dys (b) nd mturity (c) under control (C) nd drought stress (S) Stndrd errors of mens re given in prenthesis. Sdore 1991.

64 58 TNC (g) Legend IO Tiller (15) B^ Pnicle CD Upper item EMS Middle stem mmm imsii Hi Lower stem 1 IC 32 Figure 6.3. Distribution of totl nonstructurl crbohydrtes (TNC) in shoots of single plnts of three genotypes (ICMVIS (IC 32), CIVT nd P3Kolo) t flowenng (), flowering + 9 dys (b) nd mturity (c) under control (C) nd drought stress (S). Stndrd errors of mens re given in prenthesis. Sdore 1991.

65 59 much higher thn unity (1.4 for ICMVIS 85332, 2.68 for CIVT nd 1.47 for P3Kolo) Crbohydrtes Under Unlimited Versus Limited Tillering The vriety CIVT ws dditionlly studied with limited (one tiller only: C) or unlimited tillering (UC). At flowering dry mtter of the min stem prts under wellirrigted conditions did not differ significntly between the two growth tretments C nd UC, but of course tiller weight did (Figure 6.4). There ws tendency for UC for slightly higher dry weights in ll other plnt prts s well. By tht time reltive TNC content ws non-significntly higher in ll plnt prts in UC. Tiller growth from flowering to mturity ws generlly nil. During the sme period tendency ws observed tht the min stem prts under UC incresed their weight. At mturity there ws no significnt difference in smple dry weight between C nd UC under irrigted conditions. Under drought stress the tiller dry weight ws significntly decresed in C. The tendency of the response to drought stress ws equl for UC s to the plnt with controlled tiller growth. A tendency of higher dry weights for UC ws observed for ll plnt prts in both inigtion tretments. The TNC content tended to be higher for C, especilly for the pnicle. Under drought stress this difference ws much smller nd not consistent (Figure 6.5). Prtitioning of dry mtter to the pnicle fter flowering ws.81 for C (see 6.3.2) but only.45 for UC under well-irrigted conditions. For bsolute TNC however this represented.96 for C, but more thn 1 for UC. Under drought stress the prtitioning coefficients were more thn unity for both growth tretments nd both dry mtter nd bsolute TNC.

66 6 dry weight (g) Figure 6 4. Dry weight of CIVT with one (C) or ll (UC) tillers under control (left) nd drought stress (nght) t flowering () nd mtunty (b) Stndrd errors of mens re given in prenthesis Sdor6 1991

67 61 TNC (g) Figure 6.5 Totl nonstructurl crbohydrtes (TNC) of CIVT with one (C) or ll (UC) tillers under control (left) nd drought stress (nght) t flowenng () nd mtunty (b) Stndrd errors of mens re given in prenthesis Sdore 1991

68 Discussion High tempertures (Squire 1989) nd inter-plnt competition is ssumed to hve mjor influence on the ssimilte prtitioning nd supply for grin filling, respectively. Ferrris nd Chrles-Edwrds (1986) found for sorghum genotypic specific liner function of cumultive rdition nd crbohydrte content. This might be the reson why the contents of crbohydrtes in the presented study re reltively low compred to similr experiments in sorghum (Powell etl. 1991). The plnting density ws high nd therefore intercepted light ws probbly lower. No light mesurements were tken in the cnopy. The removl of ll but the first tiller influenced the bsolute mount of dry weight nd TNC contents in individul plnt prts but did not chnge the strtegy of prtitioning dry mtter nd TNC to the pnicle in the well-irrigted nor the drought stress tretment. The higher mount of biomss produced by the plnt due to more tillers lso incresed the mount of crbohydrtes vilble for mobiliztion. This indictes tht tillering cn hve the dul purpose to supply the plnt with dditionl pnicles under optimum conditions nd to serve s trnsitory source under norml nd suboptimum conditions. For cerels the production, prtitioning nd trnsloction of ssimiltes fter flowering determines grin filling. Its cpcity nd flexibility under environmentl chnges is therefore responsible for grin mss nd finl grin yield. The results presented describe detiled pttern of ssimilte distribution of three millet lines under well-irrigted conditions (potentil yield) nd under postflowering drought stress. The observtion of plnt prts for dry weight ccumultion showed tht between 65% nd 1% of the dry mtter produced fter flowering ws prtitioned to the pnicle under well-irrigted conditions. This corresponds with the study of Muchow nd Wilson (1976) nd Goldsworthy (197) tht prtitioning of ssimiltes in sorghum ws bout 1 fter nthesis. Under well-irrigted conditions prtitioning of dry mtter to the pnicle fter flowering ws slightly higher thn prtitioning of bsolute TNC for ICMVIS nd P3Kolo indicting trnsformtion of nonstructurl crbohydrtes into structurl crbohydrtes.

69 63 A high prtitioning coefficient under well-irrigted conditions for the grin filling period s for the genotype ICMVIS however did not necessrily men better grin filling nd higher grin mss under drought stress. In this genotype bout 5% of the pnicle weight increse ws ttributble to remobiliztion from reserves fter flowering while only the rest ws trnslocted from current photosynthesis under drought stress. CIVT reduced in the sme period its totl biomss by the sme mount s the pnicle weight incresed (prtitioning 1.93). P3Kolo with the lowest prtitioning coefficient under well-irrigted conditions (therefore the highest vegettive growth fter flowering) needed only 15% of its pnicle weight from remobiliztion under drought stress. Seemingly, different strtegies exist to sustin grin growth under drought stress. In the present study there ws constnt level of TNC in ll plnt prts except the pnicle under well-irrigted conditions. This suggests tht photosynthtes stored in stem prts before nthesis were not exploited for grin filling. After flowering, current photosynthtes re distributed mong stem prts to mintin their level of TNC even with their use through respirtion nd remobiliztion, while the rest is trnslocted to the pnicle. Jcquinot (197) showed by lbelling of ssimiltes in millet with C,4 tht no mobiliztion of stem ssimiltes took plce fter flowering under optimum conditions. No chnge in TNC level in the stem prts during grin filling lso mens tht the sink demnd of the pnicle could be stisfied with the prtitioned current photosynthte. This however does not correspond to the findings of McCig nd Clrke (1982). They found tht TNC in whet were ccumulted in the stem even under wellirrigted conditions to mximum t nthesis, wherefter they decline. These reserves function s buffer for phse difference between time of mximum photosynthte production by the plnt nd the time of mximum requirement by the developing grin. Jcquinot (197) found tht mximl trnsloction in millet of current photosyn thesis into the pnicle tkes plce bout ten dys fter flowering. The sme ws found in this study. The bsolute mount of TNC ccumulted from FL+9 to mturity ws ctully much higher thn during the first period of grin filling. This

70 64 however seems not to ffect grin growth potentil s its dry mtter ccumultion is lmost liner (Bieler ef l. 1992) but could be due to the initil lg phse when grin growth is very smll. Genotypic differences of prtitioning of TNC to the pnicle were confirmed for the three genotypes. The prtitioning coefficients of TNC to the pnicle fter flowering showed tht for ICMVIS nd CIVT lmost ll nd for P3Kolo mjor prt of the vilble ssimiltes of current photosynthesis ws trnslocted into the pnicle s vegettive growth ws unimportnt. The sme corresponds to sorghum (Goldsworthy 197), becuse of the importnce of current photosynthesis for grin filling, leves is very desirble trit. lte senescence of Mobiliztion nd trnsloction of prenthesis nonstructurl crbohydrtes ws importnt under postflowering drought stress. The rte of grin filling, expressed by the prtitioning coefficient of dry mtter to the pnicle, exceeds the rte of totl dry mtter ccumultion necessitting net redistribution of stored ssimiltes. All three genotypes hd similr level of TNC in ll stem prts t flowering tht ws reduced by mturity. Boyer (1976) found tht low lef wter potentils s they occur in mize due to drought stress result in lrge reductions in photosyn thesis. He concludes tht grin yield which lrgely depends on current photosynthesis is more likely to be reduced when compenstion by trnsloction of ssimiltes is limited. In sorghum Fischer nd Wilson (1975 nd 1975b) confirmed tht grin yield is not limited by the storge cpcity of the grins, nor by the trnsport system moving ssimiltes to the pnicle. Accumulted ssimiltes should therefore be very importnt for millet under drought stress. This ws confirmed in some extent by Ro et l. (1978). They concluded tht the contribution of crbohydrtes to grin filling by vrious millet plnt prts decresed with drought stress while the contribution from stem sugrs incresed. Genotypic differences were found in this study in the bility of using current photosynthtes under postflowering drought stress. The pnicle s sink for TNC ws very importnt for P3Kolo nd in some extent for ICMVIS while its bility to compete with other sinks (respirtion, trnsloction into roots, trnsfor mtion in structurl crbohydrtes) ws rther low for CIVT. The reduction in totl dry mtter from flowering to mturity for CIVT, but the chnges of bsolute TNC

71 65 in ll plnt prts shows different responses to reduced photosynthesis under drought stress. All these observtions re supported by the genotypic different drought response expressed in grin yield. The pnicle of P3Kolo showed the best bility to compete with other sinks under drought stress nd therefore hd the lowest grin-yield loss.

72 66 7. Further Aspects of Plnt Development After Flowering 7.1. Introduction Additionl grin set of tiller pnicles cn compenste for reduction in yield potentil due to mid-seson drought stress (Mhlkshmi nd Bidinger, 1985), but not due to postflowering drought stress (Mhlkshmi nd Bidinger 1986). For postflowering drought stress, the reltive development of tillers tkes n inverse role. The lter tiller flowers, the less time nd wter is vilble for grin filling nd therefore the less yield is produced. Their reltive development compred to the min stem pnicle is therefore importnt. To understnd genotypic differences in drought tolernce study of the developmentl strtegy of millet genotypes is necessry. Therefore the individul vegettive growth of genotypes hs to be observed. The development of tillers, their number nd synchroniztion of flowering compred to the min stem pnicle hs to be monitored to judge their importnce to the totl yield performnce of genotype. Their performnce cn be influenced by the vilbility of soil wter nd its utiliztion by millet genotypes. The bility to extrct soil wter for plnt growth is dependent on the development of the root system. The wter supply of the crop throughout the growing period influences the verticl distribution of the root system. Blum nd Ritchie (1984) found tht in sorghum restricted penetrtion of crown roots in the dry soil surfce is compensted by enhnced development of existing roots. Thus, totl root length is comprbly little ffected. Chudhuri nd Knemsu (1985) describe tht millet hs higher root spred, nd higher wter use efficiency compred to sorghum. They observed tht millet is cpble of extrcting wter beyond depth of 3 cm. Nevertheless, Choprt (1983) reported tht most of the root dry weight of millet, like tht of other field crops, is in the top soil lyers where the min nutrient uptke tkes plce nd tht in sndy soils millet root growth goes down to 18 cm only. The mount of roots produced under well-wtered conditions nd the loction of the root system in the soil profile cn give indictions of the bility to ccess the remining wter in the soil once the rins

73 67 hve stopped. This chpter presents nd discusses the results of phenologicl nd morphologi cl development observtions for five genotypes under well-irrigted nd postflowering drought stress tretment. Observtions include bove-ground development under well-wtered nd drought stressed conditions, estimtion of yield potentil s well s description of the root system of four genotypes. Root mesurements re complemented by neutron probe mesurements of soil wter. Problems nd constrint of millet drought reserch in the Shel re discussed Mterils nd Methods Experimentl Design The trils were plnted during the hot off-seson in split-plot design with six repetitions in 199 nd ten repetitions in The min plots represented the irrigtion tretment consisting in well-irrigted tretment nd postflowering drought stress tretment. Sub-plots were genotypes which consisted in 4 rows of 5 m length,.75 m prt. For the stress plots, irrigtion ws stopped when in 5% of the plots 5% of the plnts reched flowering, simulting postflowering drought stress. The trils were plnted by hnd on ridges.75 m prt, in hills.4 m nd.25 m prt in 199 nd 1991, respectively. Thinning ws done to three plnts per hill in 199 nd to one plnt per hill in In 199 root mesurements only were crried out for the two genotypes ICMVIS nd Synth-2. In 1991 five genotypes were plnted (ICMVIS 85327, HKP, ICMVIS 85332, CIVT nd P3Kolo) for vegettive growth observtions, root mesurements were done for the first two genotypes. Fertilizer ppliction nd crop tretments for the tril in 199 re further explined in chpter 4.2 nd for the tril 1991 in chpter 6.2. The climtic environments re shown in Annex I.

74 Vegettive Growth Observtions To determine the growth of five genotypes (in 1991 only), individul plnts were smpled strting the 48th dy fter sowing. One plnt per plot ws tken weekly up to mturity. The plnts were smpled rndomly from the two middle rows. Green lef re ws mesured (Li-Cor 31 Are Meter) nd totl bove-ground biomss ws determined fter drying the smples t 7 C for 48 hours. For the observtion of the development of individul plnts the min stems of 14 plnts per plot (yield plot) were tgged fter thinning nd their flowering dte recorded. Tillers were tgged nd monitored t their flowering dte nd numbered fter their chronology of ppernce per plnt. At mturity, the pnicles of min stems, first, second, third, nd fourth tillers were hrvested seprtely, their yield nd 1 grin weight determined nd pnicle yield nd grin number per pnicle derived Root Growth Observtions In both trils 199 nd in 1991 s described bove root smples were tken t flowering of two genotypes ech yer. With n luminum tube of 7.8 cm dimeter soil smples were tken t two loctions per plot, i.e., on the hill itself (fter cutting the hill of three plnts) nd on hlf the digonl to the next hill in 199. Smples of both loctions were tken t 1 cm nd t 2 cm steps from 2-26 cm depth nd mixed for ech depth. In 1991 smples were tken t three loctions per plot, i.e., on the hill (fter cutting the one plnt), 19 cm nd 38 cm in the row. Smples were tken t 1 cm nd t 2 cm steps from 2-1 cm depth nd kept seprte. Smples were crefully wshed nd the roots deep-frozen. True root length ws mesured with sectionl trcing pper. The root dry weight ws determined fter drying for 24 hours t 7 C.

75 Neutron Probe Mesurements For nine genotypes (ICMVIS 8633, 86313, 85321, 86327, Synth-1, Synth-2, CIVT, P3Kolo nd Sdore locl) in 199 nd for the five genotypes plnted in 1991 (see 7.2.1) neutron probe ccess tubes were instlled fter plnting in the stress plots only nd covered. Neutron probe (Troxler) redings were tken in steps of 2 cm from 3-21 cm depth three dys fter the lst irrigtion nd fterwrds thrice t weekly intervls in 199, nd twice in weekly intervls in For 15 cm depth the wter content ws derived grvimetriclly. The neutron probe ws clibrted nd the redings converted to reltive wter content Results Vegettive nd Genertive Development, nd Yield Performnce Lef Are Index (LAI) ws highest t flowering nd rpidly decresed during grin filling (Figure 7.1). Drought stress enhnced lef senescence from flowering onwrds while under well-irrigted conditions lef senescence occurred bout one week lter. There were no differences between genotypes in the rte of lef senescence neither under well-irrigted nor drought stress conditions, therefore verge vlues of genotypes re presented. The results in the present study show n lmost liner dry mtter ccumultion (r=.98) in the period from 5 dys fter sowing (DAS) to 78 DAS under wellirrigted conditions (Figure 7.1). The intervl covered ten dys before flowering nd 18 dys fter flowering (59 DAS). The buildup of dry weight of the totl bove-ground biomss under drought stress conditions stopped bout one week fter flowering, then dry weight possibly even declined during lte grin filling. The dry mtter ccumultion could therefore be described s liner only from 5 to 64 DAS (r=.99).

76 1991. Sdor6 genotypes. five of verge filling, grin erly nd during flowering mtter (DM) nd dry (LAI) index re lef Green 7.1. Figure stress DM LAI * control DAS (3 i i i i i * 94 7 = (DM) SE -5 * Flowering \ j/ o >. OU 175 = (LAI) SE - 1 g/plnt LAI out. crried be could nlysis such no tiller fourth nd third second, of rte low the to Due tretments. irrigtion the of either in identified be could genotypes five the of tiller first producing of bility the for difference significnt no vrition high to Due tretments. irrigtion two the between numbers tiller ll for differences (P<.1) significnt were There respectively. conditions stress drought nd well-irrigted under grins with tiller fourth produced ech 1% nd tiller, third produced 3% nd 6% tiller, second produced 1% nd percent Sixteen grins. with tiller first produced respectively, conditions stress under drought nd conditions well-irrigted under stems min the of 37% nd 48% of verge genotypic only tht shows 7.1 Tble tretment. stress drought the in plnt per pnicles tiller.55 nd tretment irrigted the in plnt per grins with pnicles tiller.75 of verge n ws there m'2, pnicles stem min 5.3 of density plnt At 7

77 T4). _ 71 Men flowering dte for min stem pnicles ws 59 dys for both tretments. Hving no significnt differences in verge flowering dte nor dte of mturity, ll lines suffered drought stress during the sme physiologicl period. Flowering distributions of ll pnicles were not different between genotypes. The compri son of the flowering distribution of first to fourth tillers is presented s the verges only s the respective smple sizes re different (Tble 7.1). The verge flowering of first tillers ws lgging behind most, with n verge of 64 dys (Figure 7.2), while second nd third tillers flowered erlier thn first tillers with n verge of 62 dys in both tretments. Fourth tillers flowered t 65 dys under control nd 61 dys fter sowing under drought stress. Tble 7.1. Reltive production of tillers with grins first, second, third, nd fourth grde - (T1 per genotype nd inigtion tretment. Sdore well-irrigted Min stems with: drought stressed Min stems with: T1 T2 T3 T1 T2 T3 ICMVIS HKP ICMVIS CIVT P3KOIO CV% _ Totl grin yield ws significntly reduced under drought stress by 47% for ICMVIS 85332, 44% for HKP, 53% for ICMVIS 85327, 51% for CIVT nd 25% for P3Kolo. Figure 7.3 shows grin yield of individul genotypes under both irrigtion tretments ccording to min stem nd tillers. While the min stem pnicles contributed 67% to the totl grin yield under irrigted conditions this ws 79% under drought stress conditions (Figure 7.4). The contribution of tillers to totl grin yield decresed drmticlly (Tble 7.2). First tillers mde n

78 72 verge of 23% nd 15%, second tillers 7% nd 4% of the totl grin yield under well-wtered nd drought stress tretment respectively (Figure 7.4). Both grin mss nd grin number per pnicle of tillers decresed to lrger extent thn of the min stem (Tble 7.2). P3Kolo hd the lowest yield potentil but lso the lowest loss due to drought stress in ny of the prmeters compred to the other genotypes. Since there were only few plnts with third nd fourth tillers, representing only smll smple size, men or reltive reduction s presented in Tble 7.2 ws not clculted. Their totl contribution to the totl grin yield is unimportnt (1.8% nd.4% respectively under well-irrigted conditions). Dys fter Sowing Figure 7.2. Flowering distribution of five genotypes ccording to min stem (MS) nd tillers (T1-T4) under control (c) nd drought stress (s) conditions. Sdore The grin yield loss due to drought stress ws mostly due to reduced pnicle grin number nd less to reduced grin weight for min stem nd pnicles of first tillers, but inverse for pnicle of second to fourth tillers (dt not presented).

79 Grin yield (g m-2) 3 Min Stem EH Tiller 1 Tiller 2 Tiller 3 SU Tiller 4 Figure 7.3. Grin yield of genotypes (G1: ICMVIS 85332; G2: HKP; G3: ICMVIS 85327; G4: CIVT; G5: P3Kolo) under control (C) nd drought stress (S) conditions. Sdor MS 67% MS 79% T1 23% Tl 15% Figure 7.4. Averge grin yield distribution ccording to min stem (MS) nd tillers (T1-T4) under control (left) nd drought stress (right). Sdore 1991.

80 74 Tble 7.2. Pnicle yield, grin weight nd number of grins per pnicle, of five genotypes of the min stem, first nd second tiller pnicle (T1-T2)' under well-wtered conditions nd the reltive reduction (%) under drought stress given in prenthesis. Sdore Min stems T1 T2 Pnicle yield (g) ICMVIS (35) 21.4(53) 18.7(37) HKP 34.1(41) 22.6(51) 18.8(45) ICMVIS (44) 21.9(66) 19.8(49) CIVT 29.2(37) 23.2(71) 15.(51) P3Kolo 3.4(17) 24.3(39) 19.3(38) 1 grin weight (mg) ICMVIS (12) 771 (27) 725 (22) HKP 93 (22) 81 (35) 759 (19) ICMVIS (21) 783 (31) 716(28) CIVT 965 (27) 861 (37) 793 (45) P3Kok) 935 (1) 834 (25) 78 (33) Grin number pnicle ICMVIS (28) 273(38) 256(25) HKP 366 (32) 277 (37) 249 (4) ICMVIS (32) 279 (58) 282 (41) CIVT 33(2) 27(63) 187(38) P3Kob 32 (6) 292 (2) 244 (12) * T3 nd T4 hve been omitted becuse of smll smple size (see Tble 7.1) Root Growth Totl bove-ground biomss t flowering (vilble for 1991 only) nd t hrvest s well s grin yield under both irrigtion tretments of the genotypes included in the root observtion study re shown in Tble 7.3. As reported in the tril in 199 ws drought stressed just before flowering ffecting both irrigtion

81 tretments. However ICMVIS showed better vegettive growth thn Synth-2, hd higher grin yield under well-irrigted conditions nd lso less grin yield reduction under drought stress. The biomss produced by the two genotypes in 1991 ws the sme until flowering, HKP hd slightly better vegettive growth thn ICMVIS only under drought stress. Although grin yield ws slightly lower for HKP under well-irrigted conditions its reduction under drought stress (44%) ws less thn for ICMVIS (53%). Tble 7.3. Shoot biomss nd grin yield of the genotypes included in the root observtion studies under well-wtered conditions (C) nd drought stress (S). Reltive vlues under drought stress re presented in prenthesis. Sdore 199 nd Yer Genotype Biomss t flowering g/nf Biomss t hrvest g/m2 Grin yield g/m2 199 ICMVIS Synth-2 - C S C S 569 (95%) (94%) 541 (9%) (78%) 1991 HKP (67%) (56%) ICMVIS (63%) (47%) The distribution of root dry weight nd root length long the soil profile t nthesis followed similr pttern for ll genotypes in both yers. No sttisticlly significnt genotype x depth interctions could be shown. In 199 no difference between the two genotypes in depth of root penetrtion ws identified. Roots were found for both genotypes to depth of 28 cm beyond which no further smples were tken. The significnt differences between depths were to be expected since the rooting density is decresing rpidly with incresing depth. In 199, 86% nd 89% of the totl root mss of ICMVIS nd Synth-2 respectively ws observed in the top 1 cm, while the respective vlues for root length were 7% nd 72% for the sme depth (Figure 7.5). The sme cn be observed for the root

82 76 density expressed s mg/cm3 soil or cm/cm3 soil s it is shown in Annex III. Specific root length rpidly incresed with depth in the top soil lyers (Figure 7.6). It differed between the two genotypes in 2 cm to 1 cm depth. ICMVIS showed higher, but very vrible specific root length in these depths expressing very fine root system. For deeper soil lyers the vlues were similr for both genotypes. 8 Cumultive totl root length/volume (%) ) ^^^~^^ 6 Jy/ 4 - if 2 I I I i i I 1 I I i 1 I Depth Cumultive totl root dry wt/volume (%) i \ + + t i * i i \ i i i i i Depth (cm) ICMVIS Synth-2 Figure 7.5. Cumultive root density. Length () nd dry weight (b) of two genotypes. Sdore 199.

83 77 The root length densities of the two genotypes observed in 1991 re presented in Figure 7.7. Root length density is highest in the top 1 cm just beneth the plnt. Within short distnce from the plnt the root length density is lredy very low in the top soil. From depth of 4 cm downwrd differences within row nd between rows disppered becuse of some decline in vlues between rows nd shrp decline within rows. The dry mtter contribution between rows to the totl root dry mss is miniml (Annex IV). The mjor prt of root dry weight is in the top soil within rows. The specific root length tended to be higher in between rows, especilly in the top soil (Figure 7.8). Generlly, vlues incresed with depth more rpidly within rows; t 1 cm depth differences within nd in between rows hd disppered. 1 cm/g root dry weight qi 1 i i i i i i i i i 1 1 i Depth (cm) ICMVIS <- Synth-2 Figure 7.6. Specific root length of two genotypes. Sdorg 199.

84 78 1 cm/g root dry weight Depth (cm) D 1 + D 2 -*-- D 3 Figure 7.7. Root length density t interrow distnces of cm (D1), 19 cm (D2) nd 38 cm (D3) for genotype HKP () nd ICMVIS (b). Sdore 1991.

85 - I I I I I ' i 79 cm/cm3 soil \ ),8,6,4,2 + * 1,4 1,2 \ b) 1,8,6,4,2 * + *..._ Depth (cm) 8 1 d 1 D 2 D 3 Figure 7.8. Specific root length t interrow distnces of cm (D1), 19 cm (2) nd 38 cm (D3) for genotype HKP () nd ICMVIS (b). Sdore 1991.

86 - 11.3, , Neutron Probe Results In 199 the experiment suffered slightly of drought stress in the 'well-wtered' tretment due to technicl problems in irrigtion. This drought occurred in ptches only ffecting individul plots over ll blocks nd resulted in some missing plots. In the drought stress tretment, stress effects were more severe, but gin unevenly distributed resulting in visibly vrible drought-intensity. The tril in 1991 showed strong grdient in stress from one side to the other of the field. This ws obvious from visul observtion. The first neutron probe mesurements tken three nd four dys fter the lst irrigtion in 199 nd 1991 respectively, lredy showed lrge rnge of different volumetric wter content between plots. This hppened lthough wter ppliction through irrigtion t the rte of the pn evportion ws ssumed to be sufficient nd uniform cross the field. In 1991 the observed grdient ws cross the direction of the liner moving inigtion system, excluding this s probble disturbing influence. The two experiments were not plnted on the sme field in the yers 199 nd Therefore soil chrcteristics were determined to see whether they influence field cpcity in micro-environment. Soil ph in wter did not vry much cross the field nd ws 5.4 nd 4.9 in 2 cm, 4.7 nd 4.5 in 6 cm nd 4.8 t 1 cm depth in 199 nd 1991 respectively. Phosphorus s determined fter the method Bry 1 showed n verge of 24.2 ppm, 13.3 ppm nd 1. ppm in 199 nd 18.8 ppm, 2.2 ppm nd 1 ppm in 1991 for the depth of 2,6, nd 1 cm, respective ly. After the recommendtions for these soils (Btiono etl. 1991) phosphorous ws vilble in excess in ll plots. Soil texture vried slightly cross the field (determined in only). For the three sme depths it vried from 4.3 nd % cly content. Plots with higher cly frctions were the plots with low volumetric wter contents fter the lst irrigtion. Due to these vribilities no genotypic differences of wter extrction could be found. The fourth neutron probe reding in 199 (24 dys fter lst irrigtion) nd the third reding in 1991 (18 dys fter the lst irrigtion) however showed quite uniform wter contents over the whole field. The volumetric wter content t hrvest s shown in Figure 7.9 for 1991 (FL+17) vried from 1% in 1 cm depth,

87 7% - 2 nd 4% - from 2-81 cm ssuming tht wilting point for this soil must be in this rnge. The different mount of wter extrcted in ech plot ws ssumed to hve n influence on grin yield, but could not be proved sttisticlly. Vol % H2 Depth (cm) *-tr 5 - *+ * + 1 FL-3 * \ \ FL-1 * FL.17 * \ 1 * t / 2 * t I * Figure 7.9. Volumetric wter content three dys fter flowering (FL+3), one week (FL+1) nd two weeks (FL+17) lter. Sdore Discussion According to Brmel-Cox et l. (1984) the growth pttern of millet cn be described by two phses: First liner ccumultion of dry weight until 1 to 15 dys fter flowering, nd then either continued increse, no further chnge, or n pprent decrese. No cler distinction between these two phses could be mde by the present dt. The mximum of LAI t flowering corroborted with the study of Crberry nd Cmpbell (1985). The loss of dry mtter becuse of norml lef senescence fter flowering, strting with lower leves nd progress ing upwrds, ws probbly lrgely mde up by the ccelerted grin mss

88 82 ccumultion, resulting in continued increse of totl dry mss. Under drought stress the rpid decline of lef re ws explined by Boyer (1976) for grin crops s being due to low wter potentils reducing photosynthesis, enhncing lef senescence, nd so reducing the photosynthetic ctive surfce. The induction of low lef wter potentil cused n lmost immedite decrese in green lef re index in mize (Jurgens et l. 1978). Reduced lef re nd reduced photosynthesis together resulted in n insufficient ssimilte supply for the plnts' bsic mintennce. A decrese of totl dry mtter, strting bout ten dys fter flowering cn be seen s compenstory effect. The low tiller number per min stem is due to the reltively high plnting density nd the high off-seson tempertures tht re both constrints to tillering bility (Ferrris nd Chrles-Edwrds 1986b). The reson why tillers of third nd fourth grde showed erlier flowering dte thn first tillers cn probbly be explined by the fct tht only erly plnts with eriy tillers will produce high number of tillers. Plnts with lte ppering first tillers do not produce dditionl ones. This however could not be confirmed by correltion nlysis, probbly due to smll smple size of fourth grde tillers. The lower number of tiller pnicles with grins under drought stress is possibly due to the fct tht tillers were ffected by drought in n erlier stge thn min stems nd tht ssimiltes in the tillers were trnslocted to the min stem. The reltively higher grin yield loss of tiller thn min stem pnicles confirmed the importnce of the strtegy of development of genotypes. The contribution of tillers of one third to the totl grin yield under well-irrigted conditions underlines the role of tillers in expressing yield. Environmentl influences cn therefore be determining for plnt development. A long flowering rnge between min stem pnicle nd tiller pnicles is importnt for midseson drought stress (Mh lkshmi etl. 1986) but cn be disstrous for postflowering drought s this study proves. Genotypic differences however hve yet to be identified. Millet root growth hs been intensively studied for one genotype by Choprt (1983) in Senegl. Although results of root studies re very difficult to compre due to differences in the method of root smpling, Choprt's findings correspond

89 83 quite well with the observtions mde in this study for two genotypes in the environment of Sdore (Niger). It ws reported tht the penetrtion of roots to depth slows down rpidly fter pnicle development. Therefore, root penetrtion to further depth thn 28 cm s found in this study fter flowering is not very probble. Chudhuri nd Knemsu (1985) however report tht millet is cpble of extrcting wter beyond depth of 3 m. Misr nd Ngrjro (1981) confirm rooting depth of down to 3 cm. In sorghum Myers (198) reported 86-87% of the totl root mss nd 77-78% of the totl root length is locted in the top 4 cm. These figures correspond to this study only for root mss s there were found 82-85% in the sme depth nd re confirmed for millet by Choprt. For root length only 49-5% were found in the top 4 cm. This suggests tht millet hs much higher specific root length in deeper soil lyers thn sorghum. Root density is reported to be fluctuting lot long the soil profile especilly in prenthesis development (Choprt 1983), fct tht results here confirm. The distribution of roots within nd between rows gets more uniform with depth. Choprt explins tht the distnce of the roots from ech other which expresses the potentil of exploitble wter hs much lower horizontl grdient in the soil profile thn hs root length density. It is concluded tht the possibility of wter utiliztion nd nutrient uptke is similr within nd between rows. Genotypic differences were just indicted s tendencies, i.e., specific root length in the top 1 cm s n indictor of probbly more efficient wter use extrction. No reltion of biomss or grin yield to root growth could be indicted in this study. Under moisture stress Blum nd Ritchie (1984) found tht fter flowering, sorghum root growth tkes plce minly in 9-12 cm depth. Under drought stress conditions Schmidhlter nd Oertli (1987) described n incresed ssimilte ccumultion in roots. Root growth of young cerel plnts ws generlly fvored over shoot growth (Schmidhlter ef l. 1991), since roots cn mintin growth under lower tissue wter potentils thn shoots (Westgte nd Boyer 1985b). This however ws lrgely dependent on the soil chrcteristics, llowing slow dpttion of the plnt to the decresing soil wter potentils. In the sndy soils s in the present study drought stress occurs fst, therefore such n dpttion is less likely.

90 84 The first neutron probe redings fter the lst inigtion showed wide rnge of initil soil wter content mong the plots, not corresponding to ny genotype vribility. This effect ws regrded s nturl vribility in the soil microenvironment, since the pttern of vribility could not be ttributed to ny mistkes in irrigtion neither in the sprinkler type system in 199 nor in the liner moving overhed system in Soil smples nlyzed for texture showed very nrrow rnge in cly content in the top 1 cm. Whether these smll environmen tl vribilities hd n influence on the crop growth or root development, s discussed before, could not be identified. An other hypothesis tht hs to be further investigted is whether the soil wter content t flowering ws storge of inigtion wter or even residul wter from lst seson's rin (Brouwer, ICRI SAT Shelin Center, personl communiction). In ll plots however soil wter ws exploited to the sme residul content up to mturity of the crop, despite genotypes nd initil pttern of soil wter content. Therefore ll plots under drought stress hd different mount of wter vilble for the grin filling phse.

91 85 8. Generl Discussion nd Conclusions In the present study the effect of postflowering drought stress on perl millet in West Afric ws chrcterized s significnt grin yield reduction due to both reduced pnicle grin number nd grin mss. This confirms the results of Bidinger etl. (1987) with genetic mteril of Indin origin. As drought stress in the presented experiments ws imposed t flowering stge nd since the number of grins of n inflorescence is determined before flowering (Miti nd Bidinger 1981), the plnts of the control nd stress tretment hd the sme potentil in grin number nd therefore the sme opportunity to fill the sme number of grins. Hence, in the present study, gronomic nd physiologicl observtions during the drought stressed grin filling period suggested the following mech nism of genotypic individul drought response. As found by Boyer (1976) postflowering drought stress results in low lef wter potentils tht reduces or even inhibits photosynthesis. Therefore lef senes cence is enhnced nd the photosynthetic ctive surfce reduced. It ws shown tht in peri millet under optimum conditions the ssimiltes required for grin filling come lrgely from current photosynthesis, stored soluble crbohydrtes not being exploited. The prtitioning coefficients of dry mtter ccumultion in the pnicle were found close to unity corresponding to the findings in sorghum (Muchow nd Wilson 1976). However, under drought stress, current photosynthe sis is importnt only during erly grin filling until the declining ssimilte production due to reducing photosynthesis nd the demnd of other sinks thn grins re equl, llowing no trnsloction of current ssimiltes to the pnicle. Nonstructurl crbohydrtes of prenthesis photosynthesis re then mobilized nd trnslocted from the min stem nd from tillers to stisfy the sinks demnd to some extent confirming the observtions of Ro etl. (1978). This mechnism of remobiliztion results in n unchnged grin filling rte under drought stress compred to optimum conditions (Bieler etl. 1992). The smller grin mss ws found to be primrily due to reduced grin filling period nd due to exhust of ssimiltes to be trnslocted, but most probbly lso becuse of n erly

92 86 collpse of the ssimiltory pprtus. However there is genotypic strtegy to ssure grin filling by djusting grin number per pnicle for specific environ ment. A signl must be given within the plnt to bort more kernels under drought stress thn under optimum conditions. This is supported by the studies of Reed nd Singletry (1989) in mize but could not be identified in perl millet. Two fctors influencing the mount of stored ssimiltes re suggested. A lrge number of fst developing tillers cn improve grin yield under optimum conditions mking up to one third of the totl grin yield. They cn lso ct s source under sub-optimum conditions s the erlier flowering min stem pnicle my drw on the stored nd current crbohydrtes from the tillers. Therefore, grin yield of tillers under drought stress is reltively more reduced thn of the min stem. The second mechnism cn be found in the genotypic differences in the prtitioning of dry mtter s well s of soluble crbohydrtes to the pnicle. Under drought stress the prtitioning coefficient from flowering to mturity cn be n indictor for the mobiliztion nd trnsloction of stored crbohydrtes or/nd for n bility of photosynthetic ctivity under low lef wter potentils. The prtitioning coefficients under drought stress however were not relted to the prtitioning coefficients under optimum conditions. The description of the root system t flowering under optimum conditions did not indicte genotypic differences tht could influence drought response. However n dpttion of root growth to drought stress s suggested by Schmidhlter nd Oertli (1987) cn not be excluded. Under postflowering drought stress the yield development pttern of perl millet is different thn under optimum conditions. A genotype with high potentil yield does not necessrily perform better under drought stress. Furthermore no reltionship existed of yield under well-irrigted conditions (i.e., potentil yield) to ny prmeter mesured under drought stress. Therefore, grin yield of n individul genotype ffected by drought cnnot be estimted by yield relted prmeters mesured s potentil yield. Seemingly, drought reserch in generl nd screening for drought tolernce in prticulr hve necessrily to be undertken in drought nurseries. However, to chieve nturl postflowering drought stress during the riny seson in n environment where rinfll is errtic

93 87 nd the photoperiod sensitivity of millet llows only little flexibility in plnting dte is extremely difficult. A rinout shelter to control rinfll is therefore necessry or dry seson experiments, llowing high men tempertures, required to conduct ny experiment successfully. For the ltter the lck of irrigtion equipment mkes further reserch in ntionl griculturl reserch progrms in the Shelin region impossible. According to these findings postflowering drought tolernce of perl millet cn be described in the response to the bove gronomic nd physiologicl mechnisms with the bility to produce lrge grins nd/or high number of grins per pnicle. In multiple genotype tril n bove verge individul pnicle grin yield of genotype mesured under drought stress expresses positive drought response in the specific environment. This ws confirmed with the consistent correltion nlysis over yers of yield relted prmeters mesured under drought stress to lrge number of genotype specific drought response indexes (DRI) s suggested by Bidinger ef l. (1987b). It ws found tht pnicle yield under drought stress is relted to DRI but not to flowering which excludes drought escpe mechnism nd is therefore n expression of drought tolernce. Although drought stress ws imposed t 5% flowering of 5% of the plots in ll trils presented in this study, the timing nd the intensity of the drought stress could not be dequtely mesured for ech genotype due to the experimentl design. An individul genotypic performnce therefore depends on the environ ment tht consists in the flowering dte of ll the genotypes included in drought screening tril s well s the identified soil microvribility. Seemingly, repeted over yers ech genotype rected in different pttern. This results in high genotype x yer interction for pnicle yield. Together with n unstble vegettive cycle length in different environments (photoperiodic sensitivity) it ws found to be responsible for the vrible clssifiction of genotypes fter their DRI s drought tolernt or susceptible over yers. A stbility nlysis of the prmeter s suggested by Finly nd Wilkinson (1963) is therefore recommended s tool to select drought tolernt genotypes for environments with high probbility of postflowering drought stress. The yield potentil of these genotypes however might be low under optimum conditions.

94 88 Drought escpe is one of the two mechnisms besides drought tolernce nd drought voidnce describing specific rection to drought stress. Although the emphsis in this study ws on drought tolernce, the importnce of drought escpe s screening option cnnot be neglected. Short cycle genotypes selected fter their erly flowering dte re vluble contribution to work in environments with frequent drought. However it hs to be kept in mind tht this study showed reduced biomss for short cycle genotypes wht cn be risky in the Shelin environment. When mid-seson drought occurs, short cycle genotype is less flexible to compenste yield loss with its tillers. Bidinger (1987) showed further reduced yield potentil for erly lines which could not be confirmed in this study. This of course would not be in the sense to improve grin yield in the Shel where drought cn be frequent but is not occurring every seson. To develop screening method for drought tolernce therefore mens to mintin high yield potentil, exploiting the whole length of the riny seson in good yers nd to stbilize grin yield in drought prone sesons. Although drought stress is regrded s n importnt production constrint in the Shel, Pyne etl. (199) reports tht in the sndy, low input fields like they re usul in the Shel, wter supply my not be the primry limiting constrint to millet production. Penning de Vries nd Dijiteye (1982) found tht wter is limiting in grsslnd production in the northern Shel only, wheres nutrient efficiency ws more limiting in the south. Btiono etl. (1989) noted tht fertilizer is needed to improve crop production in the nutrient-poor sndy soils of the perl millet growing region in Niger. However moisture vilbility hs significnt effects on the response to fertilizers.

95 89 9. References Annerose, D.J Criteres physiologiques pour ('meliortion de I'dpttion l secheresse de I'rchide. Olegineux 43: App Ro, S., Mengesh, M.H., nd Reddy, C.R New sources of erly-mturing germplsm in pert millet. Indin Journl of Agriculturl Science. 58: Btiono, A., Christinson, C.B., nd Mokwunye, U Soil fertility mngement of the perl millet producing sndy soils of Shelin West Afric: The Niger experience. Pges in Soil, Crop nd Wter mngement systems for rinfed griculture in the sudno-shelin zone: Proceedings of n Interntionl Workshop, ICRISAT, Ptncheru, A.P , Indi. Btiono, A., Bethgen, W.E., Christinson, C.B., nd Mokwunye, A.U Comprison of five soil testing methods to estblish phosphorous sufficiency levels in soil fertilized with wter-soluble nd springly soluble P-sources. Fertilizer Reserch 28: Bidinger, F.R., Musgrve, R.B., nd Fischer, R.A Contribution of stored pre-nthesis ssimilte to grin yield in whet nd brley. Nture 27: Bidinger, F.R., Mhlkshmi, V., nd Ro, G.P.D Assessment of drought resistnce in perl millet. I Fctors ffecting yields under stress. Austrlin Journl of Agiculturl Reserch 38: Bidinger, F.R., Mhlkshmi, V., nd Ro, G.D.P. 1987b. Assessment of drought resistnce in perl millet. II Estimtion of genotype response to stress. Austrlin Journl of Agriculturl Reserch 38: Bieler, P., Fussell, L.K., nd Bidinger, F.R Grin growth of Pennisetum glucum (L.) R.Br, under well-wtered nd drought-stressed conditions. Field Crops Reserch 3: (in press) Bishnoi, O.P., Ummheshwr, V., nd Diwn Singh Het unit requirement for growth nd development of perl millet. Annls of rid zone 24: Blck, C.R., nd Squire, G.R Effects of tmospheric sturtion deficit on the stomtl conductnce of perl millet (Pennisetum typhoides S. nd H.) nd groundnut {Archis Hypoge L). Journl of Experimentl Botny 3:

96 9 Blum, A Osmotic djustment nd growth of brley genotypes under drought stress. Crop Science 29: Blum, A., Poirkov, H., Myer, J., nd Goln, G Chemicl desicction of whet plnts s simultor of postnthesis stress. I Effects of trnsloction nd kernel growth. Field Crops Reserch 6: Blum, A., nd Ritchie, J.T Effect of soil surfce wter content on sorghum root distribution in the soil. Field Crops Reserch 8: Borrell, A.K., Incoll, L. D., Simpson, R.J., nd Dlling, M.J Prtitioning of dry mtter nd the deposition nd use of stem reserves in semi dwrf whet crop. Journl of Botny : Boyer, J.S Photosynthesis t low wter potentils. Phil. Trns. R. See. Lond. 273: Brmel-cox, P.J., Andrews, D.J., Bidinger, F.R., nd Frey, K.J A rpid method of evluting growth rte in perl millet nd its weedy nd wild reltives. Crop Science 24: Bruckner, P.L., nd Frohberg, R.C Stress tolernce nd dpttion in spring whet. Crop Science 27: Bruckner, P.L., nd Frohberg, R.C. 1987b. Rte nd durtion of grin fill in spring whet. Crop Science 27: Burton, G.W., nd Powell, J.B Perl millet breeding nd cytoge netics. Adv. Agron. 12: Crberry, P.S., nd Cmpbell, L.C The growth nd development of perl millet s ffected by photoperiod. Field Crops Reserch 11: Chudhuri, U.N., nd Knemsu, E.T Growth nd wter use of sorghum nd perl millet. Field Crops Reserch 1: Choprt, J.L Etude du systeme rcinire du mil dns un sol sbleux du Senegl. Agronomie Tropicle 38: Duncn, R.R., Bockholt, A.J., nd Miller, F.R Descriptive comprison of senescent nd nonsenescent sorghum genotypes. Agronomy Journl 73: Eberhrt, S.A., nd Russell, W.A Stbility prmeters for compring vrieties. Crop Science 6:36-4.

97 91 Eghrevb, P.N Contribution of ssimilte from different lef zones to developing millet grin. Smru Journl of Agriculturl Reserch 1: Ferrris, R., nd Chrles-Edwrds, D.A A comprtive nlysis of the growth of sweet nd forge sorghum crops. I Dry mtter production, phenology nd morphology. Austrlin Journl of Agriculturl Reserch 37: Ferrris, R., nd Chrles-Edwrds, D.A. 1986b. A comprtive nlysis of the growth of sweet nd forge sorghum crops. II Accumultion of soluble crbohydrtes nd nitrogen. Austrlin Journl of Agriculturl Reserch 37: Finly, K.W., nd Wilkinson, G.N The nlysis of dpttion in plnt-breeding progrmme. Austrlin Journl of Agriculturl Reserch 14: Fischer, K.S., nd Wilson, G.L Studies of grin production in sorghum bicolor. III. The reltive importnce of ssimilte supply, grin growth cpcity nd trnsport system. Austrlin Journl of Agriculturl Reserch 26: Fischer, K.S., nd Wilson, G.L. 1975b. Studies of grin production in sorghum bicolor. IV. Some effects of incresing nd decresing photosynthesis t different stges of the plnt's development on the storge cpcity of the inflorescence. Austrlin Journl of Agriculturl Reserch 26:25-3. Fischer, R.A., nd Murer, R Drought resistnce in spring whet cultivrs. I Grin yield responses. Austrlin Journl of Agriculturl Reserch 29: Forest, F Evolution de l pluviometrie en zone soudno-shelienne u cours de l periode et consequences sur le biln hydrique des cultures pluviles u Senegl. Agronomie Tropicle 37: Fussell, L.K., nd Person, C.J Course of grin development nd its reltionship to blck region ppernce in pennisetum mericnum. Field Crops Reserch 1: Fussell, L.K., nd Person, C.J. 1978b. Effect of therml history on photosynthte trnsloction nd photosynthesis. Austrlin Journl of Plnt Physiology 5:

98 92 Fussell, L.K., nd Person, C.J Effects of grin development nd therml history on grin mturtion nd seed vigour of Pennisetum mericnum. Journl of Experimentl Botny 31: Fussell, L.K., Person, C.J., nd Normn, M.J.T Effect of temperture during vrious growth stges on grin development nd yield of pennisetum mericnum. Journl of Experimentl Botny 31: Fussell, L.K., Bidinger, F.R., nd Bieler, P Crop physiology nd breeding for drought tolernce: reserch nd development. Field Crops Reserch 27: Grci-Huidobro, J., Monteith J.L., nd Squire, G.R Time, temperture nd germintion of perl millet. I Constnt temperture. Journl of Experimentl Botny 33: Goldsworthy, P.R The sources of ssimilte for grin development in tll nd short sorghum. Journl of Agriculturl Science Cmbridge 74: Grnt, R.F., Jckson, B.S., Kiniry J.R., nd Arkin, G.F Wter deficit timing effects on yield components in mize. Agronomy Journl 81: Guirgossin, V.Y., Vn Scoyoc, S.W., nd Axtell, J.D Chemicl nd biologicl methods for grin nd forge sorghum. Dept. of Agronomy, Agric. Exp. Sttion, Purdue University, W.Lfyette, IN 4797, USA: Henson, I.E., Mhlkshmi, V., Bidinger, F.R., nd Algrswmy, G Stomtl responses of peri millet {Pennisetum mericnum (L.) Leeke), in reltion to bscisic cid nd wter stress. Journl of Experimentl Botny 32: Hume, D.J., nd Cmpbell, D.K Accumultion nd trnsloction of soluble solids in com stlks. Cndin Journl of Plnt Science 52: Jcquinot, L L nutrition crbonee du mil. I Migrtion des ssimilts crbones durnt l formtion des grins. Agronomie Tropicle 25: Johnson, D.R., nd Tnner, J.W Clcultion of the rte nd durtion of grin filling in corn. Crop Science 12:

99 93 Jones, D.B., Peterson, M.L., nd Geng, S Assocition between grin filling nd yield components in rice. Crop Science 19: Jones, M.M., Turner, N.C., nd Osmond, C.B Mechnisms of drought resistnce. In: L.G. Pleg nd D. Aspinll (ed.) The physiology nd biochemistry of drought resistnce in plnts. Acdemic Press, Austrli. Jurgens, S.K., Johnson, R.R., nd Boyer, J.S Dry mtter production nd trnsloction in mize subjected to drought during grin fill. Agronomy Journl 7: Kumr, K.A Perl millet: current sttus nd future potentil. Outlook on Agriculture 18: Mhlkshmi, V., nd Bidinger, F.R Flowering response of perl millet to wter stress during pnicle development. Annls of Applied Biology 16: Mhlkshmi, V., nd Bidinger, F.R. 1985b. Wter stress nd time of florl initition in perl millet. Journl of Agriculturl Science Cmbridge 15: Mhlkshmi, V., nd Bidinger, F.R Wter deficit during pnicle development in perl millet: Yield compenstion by tillers. Journl of Agriculturl Science Cmbridge 16: Mhlkshmi, V., Bidinger, F.R., nd Rju, D.S Effect of timing of wter deficit on perl millet. Field Crops Reserch : Mhlkshmi, V., Bidinger, F.R., nd Ro, G.D.P Timing nd intensity of wter deficits during flowering nd grin-filling in perl millet. Agronomy Journl 8: Miti, R.K., nd Bidinger, F.R Growth nd development of the peri millet plnt. ICRISAT Reserch Bulletin No.6. McCig, T.N., nd Clrke, J.M Sesonl chnges in nonstructurl crbohydrte levels of whet nd ots grown in semirid environment. Crop Science 22: Misr, R.K., nd Ngrjro, Y Wter use under different vrieties of perl millet. Journl of the Indin Society of Soil Science 29:31-36.

100 94 Muchow, R.C., nd Wilson, G.L Photosynthetic storge limittions to yield in sorghum bicolor. Austrlin Journl of Agriculturl Reserch 27: Myers, R.J.K The root system of grin sorghum crop. Field Crops Reserch 3: O'Neill, M.K., Hofmnn, W.C., nd Dobrenz, A.K Moisture stress effects on the yield nd wter use of sorghum hybrids nd their prents. Journl of Agronomy & Crop Science 159: Oertii, J.J Effects of periods of drought t different stges of growth of spring whet cultivr. In: Chllenges in - drylnd griculture globl perspective. Proceedings of the Interntionl Conference on Drylnd Frming, August 15-19, 1988, Amrillo/Bushlnd, Texs, USA. Ong, C.K Response to temperture in stnd of perl millet. Journl of Experimentl Botny 34: Ong, C.K., nd Monteith, J.L Response of perl millet to light nd temperture. Field Crops Reserch 11: Outtr, S., Jones, R.J., nd Crookston, R.K Effect of wter deficit during grin filling on the pttern of mize kernel growth nd development. Crop Science 27: Outtr, S., Jones, R.J., Crookston, R.K., nd Kjeiou, M. 1987b. Effect of drought on wter reltions of developing mize kernels. Crop Science 27: Pnde, P.C., Pokhriyl, S.C., nd Blzor Singh Heterosis in grin sink ctivity in perl millet. Indin Journl of Genetics 43: Pyne, W.A., Wendt, C.W., nd Lscno, R.J Root zone wter blnces of three low-input millet fields in Niger, West Afric. Agronomy Journl 82: Penning de Vries, F.W.T., nd Dijiteye, M.A L'elevge et I'exploittion des pturges u Shel. In: F.W.T. Penning de Vries nd M.A. Dijitrye (ed.) L productivity des pturges Sheliens. Une etude des sols, des vegettions et de I'exploittion de cette ressource nturelle. Centre for Agric. Publ. nd Documenttion, Wgeningen, The Netherlnds. Powell, J.M., Hons, F.M., nd McBee, G.G Nutrient nd crbohydrte prtitioning in sorghum stover. Agronomy Journl 83: