M. D. Hartley 1, J. F. Spears 1,3, W. D. Smith 1, L. R. Fisher 1, and J. R. Schultheis 2 INTRODUCTION

Transcription

1 RESPONSE OF FLUE-CURED TOBACCO CULTIVARS NC 71 AND NC 72 TO SEED PRIMING: I. LABORATORY EVALUATIONS OF LIGHT AND TEMPERATURE EFFECTS ON GERMINATION RATE AND SYNCHRONY M. D. Hrtley 1, J. F. Spers 1,3, W. D. Smith 1, L. R. Fisher 1, nd J. R. Schultheis 2 Seed priming is frequently used in the tobcco seed industry to increse seed germintion rte nd uniformity nd to overcome temperture imposed dormncy. However, it is not known if ll seedlots respond eqully to priming. This reserch ws conducted to evlute the influence of temperture, light, nd priming on two widely-plnted fluecured cultivrs. Experiments were conducted in 1999 nd 2000 using the flue-cured tobcco cultivrs NC 71 nd NC 72. For ech cultivr nd yer, primed nd non-primed pelleted seeds from the sme seed lot were used. Seeds were germinted t constnt 20 C, nd lternting 30/20 C, 30/15 C, nd 23/20 C in both light nd drk environments. The dys required to rech 90% germintion (D 90 ) nd modified index of synchrony (IS M ) were determined. In 1999, priming decresed the rte of germintion (higher D 90 ) nd reduced IS M for NC 71, but hd no effect on speed or uniformity of germintion of NC 72 compred with nonprimed seeds. Germintion of primed seeds of both cultivrs t 30/20 C ws significntly fster thn germintion t 30/15 C, 23/20 C nd constnt 20 C, compred with nonprimed seeds. All seeds, whether primed or non-primed, germinted better in the drk t 30/20 C nd 30/15 C thn t 23/20 C or constnt 20 C. However, priming improved the germintion of NC 71 nd NC 72 t 23/20 C nd constnt 20 C in the drk. In 2000, differences between cultivrs were not observed; however, the D 90 ws influenced by temperture nd priming. When verged cross cultivrs nd germintion tempertures, priming reduced D 90 by one dy (10 vs 9). D 90 ws lowest t 30/20 C (8 dys) followed by 23/20 C (9 dys), constnt 20 C (10 dys), nd 30/15 C (11 dys). Priming nd temperture did not effect IS M or totl percentge germintion t 14 dys fter plnting in the light. However, in the drk, constnt 20 C resulted in the lowest percentge germintion of ll tretments. In the drk, priming incresed the germintion of both cultivrs. In these experiments, the benefits of priming were not consistent between yers. Priming my be of some benefit with some vrieties, in some production yers; however, positive, consistent response over rnge of light conditions, cultivrs, nd tempertures ws not seen in this study. ADDITIONAL KEY WORDS: Nicotin tbcum, germintion enhncement, seedling emergence INTRODUCTION Seed priming is germintion enhncement technique used to modify physiologicl events during germintion or erly seedling growth (5). It llows the uptke of wter to initite the erly events of germintion, but the seed is llowed to dry before the rdicle begins to grow (11). The gols of priming re to increse the germintion rte, increse germintion percentges, llow germintion over broder rnge of environments, nd improve seedling vigor, which would ultimtely promote more uniform seedling emergence (11). Priming is n enhncement tht cn eliminte some levels of dormncy, such s the photodormncy found in severl tobcco (Nicotin tbcum) cultivrs (9,12). Ksperbuer (9) found tht light-sensitivity of tobcco seed my be temperture relted. Seeds of the cultivrs Hvn 142 nd Connecticut Brodlef germinted in the drk t 15 C (60 nd 36%, respectively), but neither cultivr hd greter thn 1% germintion t 30 C. Photodormncy of tobcco seed occurs minly in freshly hrvested seed (7). Seed stored under proper conditions for severl months, however, usully lose this dormncy (7,15). Toole (17) demonstrted tht the germintion of some photodormnt 1 Former Grdute Reserch Assistnt, Professor, Professor, nd Assistnt Professor, Deprtment of Crop Science, N. C. Stte University, Rleigh, NC , nd 2 Professor, Deprtment of Horticulturl Science, Box 7609, N. C. Stte University, Rleigh, NC Corresponding Author: J. F. Spers; E-mil: jn_spers@ncsu.edu species could be promoted by exposure to light t constnt temperture or to drkness t lternting dy/night tempertures tht mimic typicl diurnl fluctutions. Uniformity in germintion nd seedling emergence is criticl in efficient flot-system seedling production. Uneven emergence, even s few s three dys between the first emerging seedling nd the lst, reduces overll plnt usbility in the flot system (6). Previous work from plnt beds found tht 2-dy dely in emergence resulted in seedlings tht were significntly smller thn other plnts t 50 dys fter plnting (DAP) (4). Mohptr et l. (13) evluted severl seed tretments designed to improve germintion synchrony of tobcco seed. They defined n index of synchrony (IS) s the highest percentge of seed germinted in 24-hr period divided by the finl percent germintion. Their seed tretments included drk preincubtion (DPI), ltering the osmoticum by using polyethylene glycol (PEG), chilling, nd combintions of the these. Tretments tht incresed IS included vrious combintions of DPI nd chilling, but not PEG exposure. The priming method currently used for most flue-cured tobcco cultivrs is the technique of mtripriming, lso clled solid mtrix priming (Zeb Jmes F. W. Rickrd Seed Compny, personl communiction). This method uses solid crriers tht hve low mtrix potentils to mimic the nturl process of wter imbibition from soil prticles by the seed (10). Once the desired level of imbibition hs been chieved, the solid mteril is sieved wy. The mterils tht possess the necessry chrcteristics for this process cn be nturl substnces such s vermiculite nd pet moss, 6 Tobcco Science (2001/2002) 45:6-10

2 or commercilly vilble silic products like Celite nd Micro-Cel (8). While this is generl description of solid mtrix priming, ctul methods used by seed compnies re unique nd proprietry to individul compnies performing the procedures. In flue-cured tobcco, compred to non-primed seeds, primed seeds germinte t tempertures 4.5 to 6.0 C lower in the sme mount of time, or in pproximtely hlf the time when grown t 21 to 24 C (4). Cui (3) reported tht germintion of primed TN 86 seeds ws 76% t seven DAP compred to 88% t seven DAP for non-primed seed. No differences were observed between the primed nd nonprimed seed in other experiments. These dt, nd dt from Brockelhurst nd Dermn (2), suggest tht seed lots cn vry gretly in their response to priming, even within cultivr. Becuse of this vribility, the optimum priming conditions must be determined for ech seed lot in order to obtin the gretest seed-priming response. Preliminry reserch by Smith et l. (14) demonstrted differences in cultivr response to priming. For exmple, priming incresed the rte of emergence of NC 71, NC 72, nd K 394, but decresed the emergence rte for K 326 nd K 346. The objectives of this study were to determine the effects of priming on the germintion of two widely-grown flue-cured cultivrs nd to evlute the influences of temperture nd light on percent germintion s well s the rte nd synchrony of germintion. METHODS AND MATERIALS Experiments were conducted in 1999 nd 2000 using seed of flue-cured tobcco cultivrs NC 71 nd NC 72 produced in 1998 nd For ech cultivr nd production yer, primed nd non-primed pelleted seeds from the sme seed lot were obtined from F. W. Rickrd Seed Compny. Priming method nd pelleting mterils were similr for given yer; however, compny procedures re proprietry nd my hve vried between cultivrs nd Tble 1. yers. The germintion experiments were rrnged in fourwy fctoril design with temperture, priming, cultivr, nd light s the four min vribles. Temperture tretments included constnt 20 C nd lternting dy/night regimes (8 hour dy/16 hour night) of 30/20 C, the stndrd Assocition of Officil Seed Anlysts procedure (1), nd 30/15 C, nd 23/20 C. Ech germintor contined coolwhite 110-wtt GE fluorescent bulbs (30 µmol m -2 s -1 ) tht remined lit during the eight-hour dy period. Fifty seeds were plced in 100 x 15 mm sterile plstic Petri dish contining one 15 mm blue blotter pper soked with 7 ml of distilled wter. Petri dishes contining seeds tht received the light tretment were plced inside smll cler plstic bgs to prevent moisture loss. Drk tretment dishes were wrpped in hevy-duty luminum foil to prevent light penetrtion nd reduce moisture loss. Dt for light receiving tretments were collected beginning on dy six nd ending 14 DAP. Seeds were considered germinted when the cotyledons were visible. The dys required to rech 90% germintion (D 90 ) were determined from dily counts. A modified index of synchrony (IS M ) ws determined using procedure developed by Mohptr et l. (13). To better fit our study, we modified the IS formul to the highest percentge of seed germinted in ny 48-hr period divided by the finl germintion percentge (IS M ). Drk tretments were evluted only once t 14 DAP. All dt were subjected to n nlysis of vrince (ANOVA). The dy 14 germintion counts were nlyzed s four-wy fctoril. The reminder of the dt ws nlyzed s three-wy fctoril consisting of cultivr, priming, nd temperture. RESULTS Effects of priming nd temperture on NC 71 nd NC 72 on dys to 90% germintion (D 90 ) nd modified index of synchrony (IS M ), Cultivr Priming (+/-) Germintion Temperture 30/20 C 30/15 C 23/20 C 20 C Men D 90 NC 71 Primed NC 72 Primed b NC 71 Non-primed b NC 72 Non-primed b Men b 8.94b b c IS M NC 71 Primed b NC 72 Primed NC 71 Non-primed NC 72 Non-primed Men (NS) d Time required to rech 90% germintion. A seed ws considered to hve germinted when the cotyledons were visible. b LSD (0.05) for D 90 = c Vlue determined by tking the highest percent germintion during ny 48-hour period nd dividing by the finl germintion percentge. d LSD (0.05) IS M = Experiment I, 1999 The min effects of temperture, priming, nd cultivr significntly ffected D 90 nd IS M. Two- nd three-wy interctions were not significnt except for the priming by cultivr interction for D 90 nd IS M (Tble 1). Primed NC 71 seeds required two more dys to chieve 90% germintion compred to non-primed seeds while there were no differences in D 90 between primed nd non-primed NC 72 seed. The IS M for primed NC 71 seeds ws 20 percentge points lower thn non-primed NC 71 seeds. In comprison, primed NC 72 seed IS M ws only 4 percentge points lower thn non-primed seeds of the sme seed lot. The 30/20 C tretment required only 9 dys to rech D 90 compred to 11 dys for 30/15 C nd constnt 20 C tretments (Figure 1). Germintion curves were similr for ll cultivr nd priming tretments t specific temperture regime. Germintion of NC 71 primed seed ws the slowest t ll temperture regimes. Differences in dily germintion for 30/20 C nd 30/15 C were no longer significnt by dy 12. Tobcco Science (2001/2002) 45:6-10 7

3 There ws highly significnt (P = ) priming by cultivr by temperture by light interction on germintion t dy 14 (Tble 2). There ws no difference between germintion of seed in light or drk tretments exposed to 30/20 C or 30/15 C. However, seed, especilly the nonprimed seeds, plced in drk conditions t 23/20 C nd constnt 20 C germinted more slowly thn t other tempertures. Upon completion of the drk germintion experiment (14 DAP), non-germinted seeds redily germinted when exposed to light (dt not shown). Therefore, the non-germinted seeds were still vible. NC 71 primed seed exposed to the 23/20 C nd 20/20 C drk tretments verged 78% germintion, while NC 71 nonprimed verged 24%. Under identicl conditions, primed nd non-primed seeds of NC 72 verged 86% nd 63% germintion in the drk. Tble 2. Effects of priming, temperture, nd light on germintion t 14 dys fter plnting of NC 71 nd NC 72, Germintion (%) Cultivr Priming Temperture Light Drk NC 71 Primed 30/20 C /15 C /20 C C NC 71 Non-primed 30/20 C /15 C /20 C C NC 72 Primed 30/20 C /15 C /20 C C NC 72 Non-primed 30/20 C /15 C /20 C C LSD (0.05) 8.0 LSD vlue is for comprison within nd between columns. Tble 3. Experiment II, 2000 There ws priming by cultivr by temperture interction for IS M (Tble 3). There were no significnt min effects of temperture, priming, or cultivr on IS M or ny significnt two-wy interctions. Only the min effects of temperture nd priming hd significnt effect on D 90. For exmple, seeds of the 30/20 C tretment reched D 90 t 8 dys, while they took 11 dys t 30/15 C. Temperture lso ffected germintion rte (Figure 2). Ech grph shows similr shped germintion curve for ll of the cultivrs nd priming tretments within specific temperture regimes. At the low temperture regimes, 23/20 C nd constnt 20 C, NC 71 primed seeds germinted fster thn the non-primed seeds. In 2000, significnt interctions included temperture by light nd priming by cultivr by light (Tble 4). The presence or lck of light ws the leding contributor to both significnt interctions. In the temperture by light interction, seeds exposed to 30/20 C, 30/15 C, or 23/20 C nd drkness hd germintion similr to their respective light tretments. Seed germinted t constnt 20 C in the drk hd significntly lower germintion t 14 DAP thn ll other light/drk temperture tretments. In the priming by cultivr by light interction, NC 71 non-primed seeds verged only 74% germintion in the drk compred to 82% with NC 72 primed seeds. Regrdless of cultivr or the use of or lck of priming, seed germintion ws reduced in the bsence of light compred to those tretments with light. When evluted 14 DAP, ungerminted seed from drk tretments were vible nd germinted rpidly following exposure to light (dt not shown). DISCUSSION Effects of priming nd temperture on NC 71 nd NC 72 on dys to 90% germintion (D 90 ) nd modified index of synchrony (IS M ), Cultivr / Priming Germintion Temperture 30/20 C 30/15 C 23/20 C 20 C Men D 90 NC 71 Primed NC 72 Primed b NC 71 Non-primed NC 72 Non-primed Men b 7.25c b 9.50b c,d IS M NC 71 Primed 90.00bcd b 92.50bcd NC 72 Primed 94.50bc 85.00d 95.00bc 92.00bcd NC 71 Non-primed 87.25cd 89.00bcd 93.00bcd 89.25cd NC 72 Non-primed 98.00b 95.25bc 92.75bcd 88.00cd Time required to rech 90% germintion. A seed ws considered to hve germinted when the cotyledons were visible. b LSD (0.05) for D 90 = c Vlue determined by tking the highest percent germintion during ny 48-hour period nd dividing by the finl germintion percentge. d LSD (0.05) IS M = According to Smith et l. (14), 93% of the tobcco trnsplnts used in North Crolin re produced in flot system greenhouses. As with other plnt species where trnsplnts re used, it is extremely importnt tht uniform seed germintion occurs. Seed lots tht germinte over n extended period re susceptible to stnd loss from soluble slts, resulting in empty cells, or non-usble plnts. In seprte study (6) we showed tht trnsplnt usbility in the flot system is reduced with s little s three-dy dely in emergence on 25% of the seedlings. A primry gol of seed priming is to increse germintion rte; therefore, to be dvntgeous, primed seeds used in our study should rech 90% germintion more rpidly thn non-primed seeds. In 1999, priming ctully hd negtive effect on the speed of germintion (D 90 ) for the NC 71 seedlot. Slower germintion of primed seeds ws observed t ll tempertures, but ws prticulrly noticeble when seeds were subjected to cool night tempertures (30/15 C) or when exposed to 23/20 C regime. In contrst, priming the NC seedlot offered no dvntge or 8 Tobcco Science (2001/2002) 45:6-10

4 Figure 1. Effect of priming on germintion of 1999 seed of NC 71 nd NC 72 t 30/20 C, 30/15 C, 23/20 C nd constnt 20 C. Figure 2. Effect of priming on germintion of 2000 seed of NC 71 nd NC 72 t 30/20 C, 30/15 C, 23/20 C nd constnt 20 C. disdvntge, regrdless of germintion temperture. In 2000, primed seeds of both cultivrs resulted in fster germintion t the 23/20 C tretment, but hd no effect on Tble 4. Effects of priming, temperture, nd light on germintion t 14 dys fter plnting (DAP) of NC 71 nd NC 72, Tretment Germintion (%) Light Drk 30/20 C /15 C /20 C C LSD (0.05) 5.8 NC 71 Primed NC 71 Non-primed NC 72 Primed NC 72 Non-primed LSD (0.05) 4.0 LSD vlue is for comprison within nd between columns. D 90 t ny other temperture tretment. From these dt, it ppers tht priming did not consistently improve the speed of germintion nd did in fct slow germintion in the 1999 NC 71 seedlot. Becuse of its impct on trnsplnt usbility, germintion synchrony is more criticl in the trnsplnt industry thn is speed of germintion. The two cultivrs nd seedlots (two production yers) used in this study responded differently to priming in their synchrony of germintion (IS M ). The IS M of NC 71 primed seeds in 1999 ws lower thn for non-primed t ll germintion tempertures. Priming influenced germintion synchrony of the 1999 NC 72 seedlot only when seeds were exposed to constnt 20 C, while IS M of primed seeds ws reduced considerbly compred to non-primed seeds. In the yer 2000, the NC 71 seedlot showed positive response to priming only t the 30/15 C temperture tretment, while primed NC 72 seeds t the sme temperture tretment resulted in significntly lower germintion synchrony. Tobcco Science (2001/2002) 45:6-10 9

5 The synchrony of germintion ppers to be influenced more by cultivr nd yer of seed production thn by germintion temperture. The combintion of priming nd cool night temperture of the 30/15 C tretment resulted in decresed synchrony in the 1999 NC 71 nd 2000 NC 72 seedlots. Priming, however, did not influence germintion synchrony of the NC seedlot nd ctully incresed germintion synchrony of the NC seedlot. Temperture plyed mjor role in germintion in light nd drk tretments. More idel temperture regimes, such s 30/20 C, resulted in more rpid germintion nd emergence thn priming lone. Also, lternting tempertures, s seen in the 30/20 C nd 30/15 C tretments, ws more importnt to germintion in the drk thn priming. Temperture considertions seem to be most importnt for enhncing the speed of seed germintion. These dt strongly suggest tht the effects of priming on germintion rte nd on germintion synchrony depends on individul seedlots. The decision of whether to prime given seedlot should be bsed on the performnce potentil of ech cultivr in every production environment nd should not be blnket tretment for ll seeds. Our study lso demonstrted the importnce of temperture on tobcco seed germintion rte, with cool night tempertures resulting in slower germintion. ACKNOWLEDGMENTS 4. Cundiff, J.S., A.S Csinos, nd S.C. Phtk Vribility in tobcco seedling growth relted to dy of emergence. Tob. Sci. 22: Hlmer, P Commercil seed tretment technology. Pges in: Seed Technology nd its Biologicl Bsis. Sheffield Acdemic Press, Sheffield, UK. 6. Hrtley, M.D., W.D. Smith, J.F. Spers, L.R. Fisher, nd J. R. Schultheis. 2001/2002. Effect of the uniformity of seedling emergence on the percentge of usble trnsplnts produced in tobcco flot system. Tob. Sci. 45: Hutchens, T.W Tobcco seed. Pges in: Tobcco Production, Chemistry nd Technology. Blckwell Science Ltd. Oxford, UK. 8. Khn, A.A Preplnt physiologicl seed conditioning. Hortic. Rev. 13: Ksperbuer, M.J Germintion of tobcco seed I. Inconsistency of light sensitivity. Tob. Sci. 12: Kubik, K.K., J.A. Estin, nd K.M. Eskridge Solid mtrix priming of tomto nd pepper. Proceedings of the Interntionl Conference on Stnd Estblishment. Amer. Soc. Hort. Sci. pp McDonld, M.B Seed priming. Pges in: Seed Technology nd its Biologicl Bsis. Sheffield Acdemic Press, Sheffield, UK. 12. Mohptr, S.C., nd W.H. Johnson Developmentl physiology of the tobcco seedling. I. Reltionship between moisture uptke nd light requirement during seed germintion. Tob. Res. (Indi) 4: Mohptr, S.C., J. Arcil, W.H. Johnson, nd L.A. Nelson Induction of tobcco seed germintion synchrony through drk preincubtion. Agron. J. 79: The uthors cknowledge the finncil support of Profigen, Inc. nd the North Crolin Reserch Commission. Tobcco seeds were provided by F. W. Rickrd Seeds. The uthors lso thnk Ms. B. T. Penny for technicl ssistnce. 14. Smith, W.D., L.R. Fisher, nd M.D. Boyette LITERATURE CITED 1. Assocition of Officil Seed Anlysts Rules for Testing Seeds. J. Seed Technol. 16:1-113 (revised). 2. Brocklehurst, P.A., nd J. Dermen Interctions between seed priming tretments nd nine lots of crrot, celery, nd onion. I. Lbortory germintion. Ann. Appl. Biol. 102: Ciu, M Seed germintion nd seedling development of burley tobcco in greenhouse flot system. MS Thesis. University of Kentucky. Trnsplnt production in the flot system Flue-Cured Tobcco Informtion. N.C. Coop. Ext. Serv. Bull. AG 187 (revised). 15. Steinberg, R.A Production nd germintion of Nicotin seed grown under vrious greenhouse conditions. Tob. Sci. 4: Thoms J.F., nd Rper, C.D Differences in progeny of tobcco due to temperture tretment of the mother plnt. Tob. Sci. 19: Toole, V.K Effects of light, temperture, nd their interctions on the germintion of seeds. Seed Sci. Technol. 1: Tobcco Science (2001/2002) 45:6-10

6 Tobcco Science (2001/2002) 45: