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1 Crop Protection xxx (29) 1 7 Contents lists ville t ScienceDirect Crop Protection journl homepge: Pthogenicity of Scutellonem rdys popultions from different geogrphicl res in Benin on ym (Dioscore spp.) Hugues Bimey, *, Dnny Coyne, Nico Luschgne c,1 IITA-Cotonou Sttion, Benin 8 BP 932 Cotonou, Benin IITA-Kmpl sttion, Ugnd c Deprtment of Microiology nd Plnt Pthology, University of Pretori, South Afric rticle info strct Article history: Received 24 June 28 Received in revised form 18 My 29 Accepted 19 My 29 Keywords: Nemtodes Benin Dioscore spp. Pthogenicity Scutellonem rdys is the most importnt nemtode species ffecting ym production in Benin. Two experiments were conducted to ssess the vrition in pthogenicity of three seprte popultions of S. rdys (IsoSve, IsoToui nd IsoGlz) on seven ym cultivrs of three species: Kpoun, Tne, TDr131, Moroko (Dioscore rotundt), Bnioure, Kokoro (D. cyenensis) nd Aloungn (D. lt). This ws done over two consecutive ym growing sesons; t the Interntionl Institute of Tropicl Agriculture (IITA) Cotonou Sttion, Benin experimentl frm nd in frmer s field t Sve in centrl Benin. S. rdys popultions were otined from ym originting from different geogrphicl res of Sve nd Toui in the northern Guine svnnh nd Glzoue in the southern Guine svnnh, respectively. Four-week-old plnts were ech inoculted with c. 1 S. rdys juveniles nd dults in chopped, infected pieces of ym peel. The experiments were hrvested t 9 nd 1 months fter plnting, respectively, t IITA nd Sve. Some differences were oserved in the pthogenicity of the different nemtode popultions, lthough differences were not consistent etween experiments nd etween ym cultivrs. At hrvest, in 22 23, the vrious S. rdys popultions did not ffect tuer weight, numer of tuers produced or dry rot severity on the tuers. Highest nemtode popultion density ws oserved with IsoGlz, nd Bnioure ws the ym cultivr most susceptile to nemtode infesttion. In 23 24, nemtode inocultion reduced (P.5) tuer weight for ym cv s Aloungn, Moroko nd TDr131. Weights of tuers from IsoToui- nd IsoSve-inoculted plnts were lower thn those from control plnts. Dry rot severity ws more pronounced on cv s Moroko nd TDr131 tuers thn on cv s Aloungn nd Bnioure, while no dry rot symptoms were oserved on cv Tne tuers. IsoToui nd IsoGlz cused higher (P.5) tuer dry rot severity thn IsoSve. Differences in nemtode popultion densities occurred cross S. rdys popultions for cv s Tne, TDr131 nd Aloungn with IsoSve resulting in the highest nemtode popultion densities on cv s Aloungn nd TDr131. IsoToui cused the highest percentge weight loss. During 5 months storge, infected tuers lost more (P.5) weight thn uninfected control tuers. The differences in weight loss of infected tuers differed on tuers infected y the vrious nemtode popultions. Nemtode multipliction during the storge period lso differed mong popultions. Crown Copyright Ó 29 Pulished y Elsevier Ltd. All rights reserved. 1. Introduction Ym (Dioscore spp.) is one of the most populr nd widely consumed foods in the world. It plys stple role in the diets of mny countries, notly those in Afric, South Americ, the Pcific Islnds, nd the West Indies. In 24, 36.9 million tonnes of ym were produced glolly, of which 95.8% ws hrvested in Afric. In * Corresponding uthor. Tel.: þ ; fx: þ E-mil ddresses: himey@yhoo.fr (H. Bimey), d.coyne@cgir.org (D. Coyne), Nico.Luschgne@up.c.z (N. Luschgne). 1 Tel.: þ ; fx: þ Afric, Benin is the fourth lrgest producer of ym with 2.5 mt fter Nigeri (27 mt), Ghn (3.8 mt) nd Côte d Ivoire (3 mt) (FAOstt, 24). Ym is cultivted in the centrl nd the northern prts of Benin (96.8% of totl ym production re), which is chrcterised y diversity of soil types (minerl, ferruginous, ferrlitic, hydromorphic, vertisols), climte (eninese, su-sudnin, tropicl sudnin, tcorin) nd vegettion (fllow, mngrove swmp) (Adm nd Boko, 1993; Dnsi et l., 23). Also, numerous cultivrs of different ym species re cultivted in Benin, where culturl prctices differ mong regions nd ccording to ethnic hits (Vernier, 21) /$ see front mtter Crown Copyright Ó 29 Pulished y Elsevier Ltd. All rights reserved. Plese cite this rticle in press s: Bimey, H., et l., Pthogenicity of Scutellonem rdys popultions from different..., Crop Protection (29),

2 2 H. Bimey et l. / Crop Protection xxx (29) 1 7 Scutellonem rdys (Steiner nd LeHew) Andrssy, the cusl gent of dry rot, is mongst the most importnt constrints tht chllenge ym production in West Afric (Bridge, 1982). During storge, secondry orgnisms such s mites, fungi or cteri soon invde the shllow lesions cused y the feeding of the nemtode. This leds to the more extensive, internl decy of tuers known s wet rot (Adeniji, 197). A study on the distriution, popultion density nd incidence of plnt prsitic nemtodes nd ssocited dmge of mrketed ym on mrket stlls in severl West Africn countries during 22 nd 23 demonstrted the presence of S. rdys on mrketed ym in ll countries ssessed (Coyne et l., 25). In Benin, S. rdys ws first reported on ym in 1992 (Sturhn, 1992) nd hs een found to e the most importnt nemtode ffecting the crop in the country (IITA, 1999). Identifiction of S. rdys continues to rely on morphologicl chrcters. However, lthough only S. rdys, within the genus Scutellonem, is reported to ffect ym nd cuse dry rot, Scutellonem clthricudtum Whitehed nd Scutellonem cvenessi Sher re closely relted, occur in West Afric, re morphologiclly similr nd re esily confused, creting certin txonomic confusion (Bujrd nd Mrtiny, 1995). Trditionl pproches in nemtode dignosis re time consuming nd expensive nd results from these my not e unequivocl (Dhillon, 1998). Key descriptive chrcters cn often vry considerly etween nemtode species nd mong rces of the sme species (Whitehed, 1968). Recently, moleculr studies on S. rdys popultions extrcted from different ym cultivrs collected throughout West Afric, including Benin, showed high levels of polymorphism nd morphologicl vriility (Coyne et l., 25). To dte, however, it is not known whether vriility in pthogenicity of S. rdys exists etween different isoltes or geogrphic popultions, nd if so, to wht extent this is relted to ym cultivr. Selection of representtive nemtode popultion is criticl for ny resistnce screening procedure (Bouquet et l., 1975). Aggressive popultions should e selected for screening purposes to detect genotypes possessing the highest level of nemtode resistnce, while rnge of popultions to screen ginst cn improve the resistnce selection process. The ojectives of the current study were firstly to ssess the vriility of three Benin S. rdys popultions in terms of pthogenicity on ym pre- nd post-hrvest, in reltion to ym cultivr, sed on seven common ym cultivrs cultivted in Benin. 2. Mterils nd methods 2.1. Experimentl sites nd climtic conditions The experiments were locted t the Interntionl Institute of Tropicl Agriculture (IITA) Cotonou Sttion, Benin experimentl frm during nd on frmer s field t Sve in centrl Benin during IITA-Cotonou Sttion is locted in the costl svnnh zone t 6.25 N, 2.19 E, with n ltitude of 23 m ove se level. The climte is su-equtoril nd the soil is of hydromorphic nture, which is derived from nd representtive of lowlnd sesonlly flooded res (Adm nd Boko, 1993) nd chrcterised y N.5%, P 2 O 5.27 ppm, K 2 O.2 meq for 1 g soil, C.6%, ph 6.18, nd C/N rtio of 5.37 (Mhouge, 1996). The minimum totl monthly rinfll during the experimentl period ws 32 mm, recorded in June 22 nd the mximum 393 mm, recorded in August 22. The minimum verge dily temperture during the experiment ws 24 C nd the mximum 32 C. The Sve site is locted in the northern Guine svnnh t 8.26 N, 2.22 E, chrcterised y ferruginous soil, nd su-sudnin climte (Adm nd Boko, 1993). The minimum totl monthly rinfll ws 22 mm nd the mximum 236 mm. The minimum verge dily temperture during the experiment ws 25 C nd the mximum 33 C Experimentl design nd detils The experiments comprised two fctors: nemtode popultion nd ym cultivr. The fctor nemtode popultion hd four tretment levels t oth experimentl sites: three seprte geogrphicl popultions of S. rdys from three loclities nmely Sve, Toui nd Glzoue in Benin nd n uninfected control. The fctor ym cultivr hd four tretment levels t IITA: cv s Bnioure, Kokoro, Kpoun nd Tne nd five t Sve: cv s Bnioure, Aloungn, TDr131, Moroko nd Tne. At oth sites, rndomised complete lock design ws used with three replictes. Ym tuers weighing 4 5 g ech (size-1 tuers) were used for plnting throughout the study. The tuers were hot-wtertreted t 5 C for 3 min (Smit, 1967) to eliminte S. rdys nd they were pre-sprouted to ensure plnt uniformity. In the experiment, ym cv s Bnioure nd Kokoro (D. cyenensis), Kpoun nd Tne (D. rotundt) were sourced from frmer t In villge in the north est of Benin nd plnted t IITA during April 22. During April 23, the experiment ws repeted t Sve using cv s Bnioure (D. cyenensis), Aloungn (D. lt), TDr131, Moroko nd Tne (D. rotundt). Tuers of cv s Bnioure nd Tne from the hrvests were used for plnting mteril in 23. Tuers of cv TDr131 were otined from IITA- Idn, Nigeri, while cv s Aloungn nd Moroko tuers were collected from In experimentl sttion of the Benin Ntionl Institute of Agriculturl Reserch (INRAB). For ech of the two experiments, in ech lock, five ym tuers were plnted per cultivr for ech S. rdys popultion. Tuers were plnted in mounds (c cm height) prepred y gthering the surrounding top lyer of soil. The plnts were stked (one stke per plnt) three weeks fter plnting. The experiments were mintined weed-free y regulr hnd weeding. For oth experiments, pre-plnt nemtode popultion densities in the soil were determined shortly efore plnting. Soil smples were tken from 3 m 2 m res reserved for the experiments. Using trowel, pproximtely 1 g soil ws collected from ech 1m 2, t depth of c cm following systemtic collection procedure (Brker nd Nilck, 199). Soil from ech 1 m 2 ws comined in plstic g nd lelled, providing totl of six ulked soil smples. Nemtodes were extrcted from 3 5 g soil su-smples for ech ulked soil smple, over 48 h y mens of modified Bermnn method (Hooper, 199). Nemtodes were identified to genus level nd popultion densities ssessed s descried elow Inoculum preprtion nd inocultion procedure Three popultions of S. rdys were used in the current study. They were otined from hevily infected ym cv Al tuers collected from Sve (8.6 N, 2.54 E) nd Toui (8.41 N, 2.41 E) in the northern Guine svnnh nd from Glzoue (7.94 N, 2.25 E) in the southern Guine svnnh in Benin. Inoculum popultion density ws determined prior to inocultion y peeling tuers mnully with kitchen peeler. Severl strips of peel were removed from different portions of the tuers, chopped nd nemtodes extrcted from 3 5 g su-smples using modified Bermnn method over 48 h (Hooper, 199). The nemtode suspension ws collected nd nemtode popultion density ssessed from three 1 ml-liquots using Leic Wild M3C stereomicroscope. From the nemtode popultion densities otined, the weight of ym peel tht contined c. 1 S. rdys juveniles nd dults (comined) for ech popultion ws clculted. Consequently, 7.3, 7.9 nd 8.2 g Plese cite this rticle in press s: Bimey, H., et l., Pthogenicity of Scutellonem rdys popultions from different..., Crop Protection (29),

3 H. Bimey et l. / Crop Protection xxx (29) S. rdys-infected ym peel (cv Al) were used, respectively, for Sve (IsoSve), Glzoue (IsoGlz) nd Toui (IsoToui) popultions, nd pplied s inoculum per plnt t the IITA site. The control tretment consisted of plnts inoculted with 7.8 g (verge of infected peel weights) of S. rdys-free ym peel of ym cv Al. At Sve, 9.6, 8.9 nd 9.3 g S. rdys-infected ym peel cv Al were pplied per plnt s inoculum for Sve, Glzoue nd Toui popultions, respectively. Control tretment plnts received ech 9.3 g of uninfected ym peel. For oth experiments, plnts were inoculted t 4 weeks fter plnting. A shllow trench ws dug t c. 5 cm rdius round the stem of ech plnt, to depth (c. 5 1 cm) tht exposed some of the roots. The chopped tuer peel ws plced round the roots nd then covered with soil (Kwoseh, 2) Assessment of crop yield prmeters Experiments were hrvested t ym mturity 9 nd 1 months fter plnting (in Decemer 22 nd in Ferury 24) t IITA nd t Sve, respectively. The weight nd numer of tuers per mound were recorded t hrvest Assessment of nemtode dmge nd popultion density Nine tuers weighing 3 4 g ech (size-2 tuers) were rndomly selected per tretment nd stored t c. 25 C(Lyong nd Ayuk-Tkem, 1982; Nwnkiti et l., 1988; Osgie, 1992). After 3 months storge, three of the nine size-2 tuers per tretment were rndomly selected nd re-weighed. Remining tuers were susequently used t 4 nd 5 months fter hrvest nd percentge weight loss clculted: 1 [(weight of tuer t ssessment period 1)/weight of tuer t hrvest]. At hrvest, size-1 tuers were ssessed for dry rot severity, while size-2 tuers were ssessed for dry rot severity oth t hrvest nd during storge. Size-1 tuers were ssessed only t hrvest s these were in insufficient quntity for ssessment t hrvest nd during storge. Three tuers were ssessed per tretment in lock. Dry rot ws scored ccording to n ritrry scle of 4: ¼ clen tuer; 1 4 ¼ tuer skin showing dry rot symptoms; 1 ¼ 1 25% low symptoms of dmge; 2 ¼ 26 5% low to moderte symptoms of dmge; 3 ¼ 51 75% moderte to severe symptoms of dmge; 4 ¼ 76 1% highly severe symptoms of dmge. Tuer nemtode popultion densities were determined t hrvest nd during storge (t 3, 4 nd 5 months fter hrvest). For ech ssessment, nemtode popultion density ws determined from three tuers, rndomly selected per tretment s previously descried. Size-2 tuers were ssessed t hrvest nd t monthly intervls etween 3 nd 5 months. This ws undertken in order to compre nemtode popultion densities on different sized tuers t hrvest. Insufficient size-1 tuers prevented such comprisons during storge. Nemtode popultion densities were ssessed from the sme size-2 tuers for which weight loss ssessments were mde Dt nlyses Differences in nemtode popultion densities nd percentge weight loss in tuers etween tretments were compred with ANOVA, using the SAS system, Version 8 for Windows 1999, following log 1 (xþ1) trnsformtion of nemtode popultion densities nd rcsine(x) trnsformtion of percentge weight loss. Tretment mens were seprted y Fisher s protected lest significnt difference (LSD) test or Stndrd Error, P Results 3.1. Assessment of crop yield nd nemtode dmge t hrvest In the experiment, there were no differences in yield per plnt (P.5) mong S. rdys popultions (Tle 1). In 23 24, yields of infected cv Bnioure nd cv Tne plnts were similr ut the men plnt yield ws greter for the control plnts for cv s Aloungn, Moroko nd TDr131. Plnt yield differences etween nemtode popultions were oserved for cv s Aloungn, Moroko nd TDr131. The men plnt yield clculted cross ym cultivrs indicted no yield differences etween nemtode tretments in In 23 24, differences in tuer yield were oserved etween plnts inoculted with IsoToui nd tht of plnts inoculted with IsoGlz nd of control plnts nd there were yield differences etween plnts inoculted with IsoSve nd tht of control plnts (Tle 1). For oth experiments, the numer of tuers produced did not differ mong S. rdys popultions, except for cv Tne in (dt not shown). In 22 23, tuers presented no symptoms of dry rot t hrvest (dt not shown). In 23 24, cv s Aloungn nd Bnioure tuers from plnts inoculted, respectively, with IsoToui nd IsoGlz hd low levels of dmge. Tuers of from plnts of cv s Moroko nd TDr131 inoculted with IsoToui nd IsoGlz were modertely (P.5) ffected, ut IsoSve-inoculted plnts hd only low (P.5) levels of dmge. No symptoms of dry rot were recorded from cv Tne tuers. The men vlue of tuer dry rot severity clculted cross ym cultivrs indicted higher vlues for IsoToui- nd Iso- Glz-inoculted plnts thn for IsoSve-inoculted nd control plnts. Dry rot severity ws highest on Moroko nd TDr131 tuers nd lowest on Bnioure nd Tne tuers (Tle 2) Assessment of nemtode popultion density prior to plnting nd t hrvest No S. rdys were recovered from the soil during the pre-plnt ssessment t either the IITA or Sve site. During the experiment, the highest (P.5) nemtode popultion densities t hrvest on size-1 tuers were recorded for IsoGlz on cv Tne. The highest men nemtode popultion density ws lso recorded for IsoGlz. For the other ym cultivrs, popultion densities were similr cross S. rdys popultions. Cultivr Bnioure ws the most susceptile to S. rdys popultions (Tle 3). In 23 24, the popultion densities for the different nemtode popultions differed mong ym cultivrs (Tle 3). For cv s TDr131 nd Aloungn, higher (P.5) nemtode popultion densities were recorded with IsoSve thn with other nemtode popultions. Popultion densities were similr for the three nemtode popultions on cv s Bnioure nd Moroko tuers. In cv Tne tuers, IsoToui multipliction ws lower (P.5) thn tht of IsoGlz or IsoSve. Reltively lower nemtode popultion densities were recovered from ll cultivrs tested in (except for cv TDr131) thn in The highest men nemtode popultion density ws recorded with IsoSve, with TDr131 ppering the most susceptile ym cultivr (Tle 3). S. rdys popultion densities on size-1 tuers were higher thn those on size-2 tuers for oth experiments, except for IsoGlz, for which the popultion density ws higher on size-2 tuers t IITA (Tle 4). In the experiment, t hrvest, the popultion density of IsoGlz on the size-2 tuers ws higher (P.5) thn tht of IsoSve or IsoToui (Fig. 1). In the experiment, no differences in nemtode popultion densities were oserved mong the three popultions (Fig. 1). In oth experiments, few nemtodes were recovered from uninoculted control tuers (Fig. 1). Plese cite this rticle in press s: Bimey, H., et l., Pthogenicity of Scutellonem rdys popultions from different..., Crop Protection (29),

4 4 H. Bimey et l. / Crop Protection xxx (29) 1 7 Tle 1 Effect of three Scutellonem rdys popultions on men yield per plnt (g) of seven ym cultivrs plnted t two sites in Benin over two growing sesons. () Experiment in S. rdys popultion Bnioure Kokoro Kpoun Tne Men IsoToui IsoSve IsoGlz Control s.e. ns ns ns ns ns () Experiment in S. rdys popultion Aloungn Bnioure Moroko TDr131 Tne Men IsoToui c IsoSve c IsoGlz Control s.e. 132 ns ns Vlues represent men yield (g) of tuers per plnt with totl numer of 15 plnts per cultivr nd per S. rdys popultion. IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res in Benin, respectively. ns ¼ non significnt t P.5. s.e. ¼ stndrd error. Tle 2 Tuer dry rot severity cused y three popultions of Scutellonem rdys t hrvest on five ym cultivrs during growing seson in Benin. S. rdys popultion experiment t Sve Men Aloungn Bnioure Moroko TDr131 Tne IsoToui IsoSve IsoGlz Control s.e ns ns.2.2 ns.2 Men.17 B.7 C 1.87 A 1.33 A. C IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res in Benin, respectively. Dt represent men vlues per plnt. 15 replictes were used. s.e. ¼ Stndrd Error. ns ¼ non significnt t P.5. In ech column, the men represents n verge clculted from the vlues of tuer dry rot severity for the three S. rdys popultions Assessment of nemtode popultion density, dry rot nd tuer weight loss during storge In the experiment, tuers presented no symptoms of dry rot during storge. Nevertheless, 3 months fter hrvest n increse in nemtode popultion densities ws oserved for ll three popultions. From the third month fter hrvest to conclusion of the experiment t 5 months, nemtode popultion densities decresed on inoculted stored tuers for ll three popultions, with lowest (P.5) popultion densities recorded with IsoSve (Fig. 1). In the experiment, dry rot severity t hrvest nd during storge did not differ etween S. rdys popultions (P.5). Nemtode popultion densities incresed until the fourth month fter hrvest for ll three popultions nd decresed therefter. Four nd 5 months fter hrvest higher (P.5) Tle 3 Nemtode popultion density t hrvest on tuers of seven ym cultivrs inoculted with three different Scutellonem rdys popultions during two ym-growing sesons in Benin. () Experiment in S. rdys popultion Bnioure Kokoro Kpoun Tne Men IsoToui IsoSve IsoGlz Control c 6c Men 757 A 61 B 635 B 666 B ) Experiment in S. rdys popultion Aloungn Bnioure Moroko TDr131 Tne Men IsoToui IsoSve IsoGlz Control. c c c 3 c Men 132 B 167 B 185 B 552 A 181 B IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res. Vlues represent nemtode popultion densities on tuers weighing 4 5 g ech. For given ym cultivr, columns with the sme letter re not significntly different ccording to Fisher s protected LSD test, P.5. Sttisticl nlyses ws undertken on log 1 (xþ1) trnsformed dt. In ech column, the men represents n verge vlue clculted from the three S. rdys popultion densities. Plese cite this rticle in press s: Bimey, H., et l., Pthogenicity of Scutellonem rdys popultions from different..., Crop Protection (29),

5 H. Bimey et l. / Crop Protection xxx (29) Tle 4 Popultion density of three Scutellonem rdys popultions on size-1 nd size-2 ym tuers in two experiments in Benin over two growing sesons. S. rdys popultion experiment t IITA experiment t Sve Size-1 tuers Size-2 tuers Size-1 tuers Size-2 tuers Control IsoGlz IsoSve IsoToui IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res in Benin. For ech S. rdys popultion, nemtode densities followed y the sme letter in line for given experiment re not significntly different ccording to Fisher s protected LSD test, P.5; nlyses ws undertken on log 1 (xþ1) trnsformed dt. Size-1 tuers re tuers weighing 4 5 g ech t hrvest. Those tuers were not stored. Size-2 tuers re tuers weighing 3 4 g ech t hrvest nd they were stored. Dt represent nemtode popultion densities in 5 g ym tuer peel. Vlues represent men nemtode densities for four ym cultivrs t IITA nd five t Sve. Nemtode popultion density/5 g tuer B C A A A A B AB B Hrvest 3 MAH 4 MAH 5MAH Storge period B C AB Nemtode popultion density/5 g tuer B C B A IsoToui IsoSve A A IsoGlz Control B A A C A B B A Hrvest 3 MAH 4 MAH 5 MAH Storge period Fig. 1. Popultion densities on tuers during 5-month storge period t 25 C of three Scutellonem rdys popultions used to inoculte ym cultivrs plnted t IITA, Benin Sttion in 22 (Fig. 1) nd t Sve in 23 (Fig. 1) in Benin. MAH ¼ Months After Hrvest. Size of tuers t hrvest: 3 4 g. IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res. For ech S. rdys popultion, mens with the sme lower cse letter re not significntly different ccording to Fisher s protected LSD test, P.5. For ech ssessment period, mens with the sme cpitl letter re not significntly different ccording to Fisher s protected LSD test, P.5. Sttisticl nlyses ws undertken on log 1 (xþ1) trnsformed dt. popultion densities of nemtodes were recovered for IsoSve, compred with IsoToui- or IsoGlz-inoculted tuers (Fig. 1). During 22 23, 4 nd 5 months fter hrvest, no differences in size-2 tuer weight loss were recorded etween S. rdys popultion tretments. Weight loss of tuers ws not ffected (P.5) y nemtodes when compred to tuer weight loss from uninoculted control tretments. Three months fter hrvest, the gretest weight loss ws recorded for IsoSve (Fig. 2). In 23 24, ssessment t the third nd the fifth months fter hrvest showed tht tuer weight loss did not differ (P.5) etween nemtode popultion tretments. But 4 months fter hrvest, tuer weight loss ws gretest for IsoToui, followed y IsoGlz nd Iso- Sve (Fig. 2). In 22 23, the men tuer weight loss clculted cross the storge period showed differences in weight loss of tuers etween IsoSve-inoculted plnts nd IsoGlz-inoculted nd control plnts nd higher weight losses were oserved for tuers from IsoToui- nd IsoSve-inoculted plnts, compred with tuers from control plnts (Tle 5). In 23 24, differences in weight loss of tuers were oserved etween inoculted nd control plnts with the highest weight loss oserved for tuers from IsoToui-inoculted plnts (Tle 5). 4. Discussion Although the popultions used in this study ppered to multiply t different rtes, this did not ffect the numer of tuers produced or dry rot severity over the durtion of the study. The effect of the nemtodes on dry rot severity t hrvest hs lso een oserved y Ayl nd Acost (1971) nd Bridge (1973) who lso concluded tht S. rdys did not cuse reduction in yield of ym. However, they reported tht S. rdys cused mrked reduction in the mrketle vlue of the tuers during storge. The dry rot symptoms oserved on tuers from Sve, lthough no symptoms of tuer dry rot were oserved t IITA, indicte tht ym tuer dry rot is possily consequence of climte in comintion with S. rdys, which is dependent on ym cultivr. The results otined, in terms of tuer weight nd nemtode popultion density, provides further informtion tht vriility etween S. rdys popultions likely exists nd which my e relted to moleculr nd morphologicl differences (Coyne et l., 25). The fct tht popultion densities of the different popultions vried etween experiments my e relted to the conditions t ech experimentl site. Environmentl fctors such s rinfll, temperture, humidity, nd soil type (Mi, 1985; Currn et l., 1986; Ssser, 199) my e more fvourle for multipliction of the nemtodes t IITA thn t Sve. Luc nd Hoestr (196) indicted tht in West Afric, the red soil type ws more fvourle to S. rdys thn fine or corse snd soil conditions. Initition of growth of size-1 tuers my hve egun efore tht of size-2 tuers (Tourei nd Ahoussou, 1982), which my explin the erlier recorded infection of size-1 tuers nd the higher nemtode popultion densities recovered t hrvest on size- 1 tuers, compred with those on size-2 tuers. The decrese in nemtode popultion densities with durtion of storge my e relted to the high nemtode popultion densities on the tuers during those periods, leding to competition for nutrients on smll tuers (3 4 g ech). However, this does not fully explin the sitution, s nemtode popultion densities of much higher levels hve een oserved on mrketed ym in Nigeri (Bridge, 1973). The Plese cite this rticle in press s: Bimey, H., et l., Pthogenicity of Scutellonem rdys popultions from different..., Crop Protection (29),

6 6 H. Bimey et l. / Crop Protection xxx (29) 1 7 Percentge weight loss of tuers Percentge weight loss of tuers MAH 3 MAH IsoToui IsoSve IsoToui IsoSve IsoGlz Control 4 MAH Storge period c 5 MAH decrese in nemtode popultion densities during storge my lso e relted to the physiologicl chnges in the ym tuers, which cn ffect multipliction of nemtodes. Adesiyn et l. (1975) found tht the increse in monoscchrides in S. rdys-infected ym tuers explined one mode y which the nemtode predisposes ym tuers to infection y secondry pthogens (fungi nd cteri). The ctivities of these invders susequently speed up Tle 5 Men percentge weight loss of ym tuers inoculted with three popultions of Scutellonem rdys t plnting nd stored for five months fter hrvest t 25 Cin Benin. S. rdys popultion experiment t IITA experiment t Sve IsoToui IsoSve IsoGlz c Control c c IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res in Benin. Vlues for the experiments t IITA nd Sve represent, respectively, mens for four nd five ym cultivrs. Ech vlue represents men tuer weight loss for three, four nd five months of storge. For ech S. rdys popultion, tuer weight loss followed y the sme letter within column re not significntly different ccording to Fisher s protected LSD test, P.5. 4 MAH IsoGlz Control Storge period 5 MAH Fig. 2. Percentge weight loss of ym tuers inoculted with three popultions of Scutellonem rdys t plnting nd stored for 5 months fter hrvest t 25 C in Benin. Dt for experiment in re represented in Fig. 2 nd those for in Fig. 2. Ech column represents the men cross ym cultivrs per S. rdys popultion. For given ssessment period, columns with the sme letter re not significntly different t P.5 ccording to Fisher s protected LSD test. IsoToui, IsoSve nd IsoGlz ¼ S. rdys popultions from Toui, Sve nd Glzoue res. Sttisticl nlyses ws undertken on log 1 (xþ1) trnsformed dt. Size of tuers t hrvest: 3 4 g ¼ size-2. other physiologicl processes, such s respirtion nd wter loss, which cn ffect tuer storge life nd S. rdys multipliction dversely (Cdet nd Quénéhervé, 1994). This contrdicts other oservtions, however, where S. rdys popultions incresed 9- to 14-fold on D. rotundt tuers over 5 6 month storge period Bridge (1973), nd five- to eight-fold on D. lt nd D. cyenensis over similr period Adesiyn (1977). The tuers stored y Bridge (1973) nd Adesiyn (1977) were possily lrger thn those ssessed in the current study. The nemtodes recovered from the control tuers were most proly result of smll numer of nemtodes surviving the hot wter tretment of the plnting mteril nd which multiplied during the vegettive period of ym plnts nd storge of tuers. The differences in weight loss etween S. rdys-infected nd control tuers (especilly in the experiment) confirm oservtions y Wood et l. (198), who indicted tht disesed tuers hrvested from the field in Nigeri lost up to 29% more weight thn helthy tuers. Weight loss occurs during storge due to moisture loss through epiderml lyers (Ayl nd Acost, 1971; Bridge, 1973) nd s result of nturl metolic processes, such s respirtion. These metolic processes re more ccentuted in tuers infected with nemtodes (Cdet nd Quénéhervé, 1994) nd nemtode feeding sites re zones of high metolic ctivity (Jones, 1981). Vrition in pthogenicity nd the existence of host rces nd pthotypes or iotypes of plnt-prsitic nemtodes hs previously een recognised for numer of species, such s root-knot nemtodes (Meloidogyne spp.), cyst nemtodes (Heteroder spp. nd Glooder spp.) nd stem nemtodes (Ditylenchus spp.) (Strr et l., 22; Luc et l., 25) nd prticulrly for Rdopholus similis (Dochez, 24). Vrints my differ in their reproductive potentil on host species or cultivrs, which consequently hs importnt implictions for the development of pest mngement strtegies. The identifiction of iotypes or highly virulent popultions is prticulrly importnt in reeding for resistnce ginst these pests (Bkker et l., 1993). The results of the current study provide preliminry indiction tht popultions of S. rdys with different levels of virulence my exist. The results were not consistent etween experiments, ut the second yer s experiment indicted greter detrimentl effect with IsoToui nd IsoGlz on weight of tuers, percentge weight loss nd dry rot of tuers, nd nemtode popultion density thn with IsoSve. Further studies would therefore e necessry with higher initil nemtode popultion densities, nd possily more susceptile ym cultivrs to more clerly define differences etween the different S. rdys popultions. Acknowledgements Funding for this study ws provided y the Interntionl Institute of Tropicl Agriculture (IITA) s prt of PhD study y Mr. H. Bimey. The uthors grtefully cknowledge IITA. Much pprecition to Mr. Sm Korie for sttisticl support. 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