Drought, pod yield, pre-harvest Aspergillus infection and aflatoxin contamination on peanut in Niger

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1 Field Crops Reserch 98 (2006) Drought, pod yield, pre-hrvest Aspergillus infection nd fltoxin contmintion on penut in Niger P.Q. Crufurd, *, P.V.V. Prsd b, F. Wliyr c, A. Theri d The University of Reding, Plnt Environment Lbortory, Cutbush Lne, Shinfield, Reding RG2 9AF, UK b Deprtment of Agronomy, Knss Stte University, 3708 Throckmorton Hll, Mnhttn, KS 66506, USA c Interntionl Crops Reserch Institute for the Semi-Arid Tropics, Ptncheru, Andhr Prdesh , Indi d President, Gorgn University of Agriculturl Sciences nd Nturl Resources, Shhid Beheshti Avenue, Gorgn , Irn Received 16 December 2004; received in revised form 2 December 2005; ccepted 3 December 2005 Abstrct Soil moisture nd soil temperture ffect pre-hrvest infection with Aspergillus flvus nd production of fltoxin. The objectives of our field reserch in Niger, West Afric, were to: (i) exmine the effects of sowing dte nd irrigtion tretments on pod yield, infection with A. flvus nd fltoxin concentrtion; nd (ii) to quntify reltions between infection, fltoxin concentrtion nd soil moisture stress. Seed of n fltoxin susceptible penut cv. JL24 ws sown t two to four different sowing dtes under four irrigtion tretments (rinfed nd irrigtion t 7, 14 nd 21 dys intervls) between 1991 nd 1994, giving 40 different environments. Averge ir nd soil tempertures of C were fvourble for fltoxin contmintion. CROPGRO-penut model ws used to simulte the occurrence of moisture stress. The model ws ble to simulte yields of penut well over the 40 environments (r 2 = 0.67). In generl, erly sowing produced greter pod yields, s well s less infection nd lower fltoxin concentrtion. There were negtive liner reltions between infection (r 2 = 0.62) nd the verge simulted frction of extrctble soil wter (FESW) between flowering nd hrvest, nd between fltoxin concentrtion (r 2 = 0.54) nd FESW in the lst 25 dys of pod-filling. This field study confirms tht infection nd fltoxin concentrtion in penut cn be relted to the occurrence of soil moisture stress during pod-filling when soil tempertures re ner optiml for A. flvus. These reltions could form the bsis of decisionsupport system to predict the risk of fltoxin contmintion in penuts in similr environments. # 2005 Elsevier B.V. All rights reserved. Keywords: Aspergilus flvus; Afltoxin; Penut; Groundnut; Drought; Crop simultion modelling 1. Introduction Penut is n importnt crop in Niger, even though growing sesons re short nd vrible, nd drought nd high soil tempertures re common (Ntre nd Willims, 1998). Afltoxins re toxic, crcinogenic, tertogenic nd immunosuppressive substnces (Turner et l., 2000; Wild nd Hll, 2000; Hll nd Wild, 2003) produced when toxigenic strins of the fungi Aspergillus flvus Link. ex Fries nd A. prsiticus Spere grow on penuts nd mny other griculturl commodities. Afltoxin concentrtion is the most importnt qulity problem in penuts worldwide with serious helth implictions for humns s well s livestock * Corresponding uthor. Tel.: ; fx: E-mil ddress: p.q.crufurd@reding.c.uk (P.Q. Crufurd). (D Mello, 2003; Bht nd Vsnthi, 2003; Gong et l., 2003; Wliyr et l., 2003). For exmple, the mjority of children tested in recent study in West Afric who hd detectble fltoxin levels in their blood were stunted nd under weight (Gong et l., 2003). Infection of penut by Aspergillus occurs under both prehrvest nd post-hrvest conditions. Pre-hrvest infection by Aspergillus nd consequent fltoxin concentrtion is more importnt in the semi-rid tropics, especilly when drought occurs in the lst dys of the seson (e.g. Cole et l., 1989; Snders et l., 1993). In series of experiments using controlled soil temperture nd soil wter fcilities, Cole nd his co-workers (Cole et l., 1985, 1989; Dorner et l., 1989) hve shown tht pre-hrvest contmintion requires drought period of dys nd men soil temperture in the podding zone of C. Drought in the bsence of /$ see front mtter # 2005 Elsevier B.V. All rights reserved. doi: /j.fcr

2 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) high soil temperture does not result in contmintion. Shorter periods of drought (<20 dys), nd drought erly or lte in the seson, lso result in lower concentrtions of fltoxin (nd see Azizeh et l., 1989). Similrly, soil tempertures in the pod zone, not the root zone, cooler or wrmer thn C lso result in less fltoxin concentrtion (Blnkenship et l., 1984; Cole et l., 1989), even if drought is imposed. However, these reltions hve not been verified under field conditions in West Afric where fltoxin is mjor problem. The work of Cole nd his co-workers does, nonetheless, provide sound bsis for predicting fltoxin contmintion, or t lest the risk of fltoxin concentrtion bove permissible limits (e.g. >10 mg kg 1 ), if wter deficit nd soil temperture dt re vilble. Of course these dt re more often thn not vilble for experiments, nd certinly not vilble for the lrger geogrphicl res over which there would be risk from fltoxin contmintion. Therefore, crop simultion models, whether on point (experiment, field; e.g. DSSAT) or pixel (district, region; e.g. GLAM) scle will be needed to estimte wter deficit nd soil temperture (Boote et l., 1998; Chllinor et l., 2004). DSSAT-CROPGRO-penut is process oriented, mechnistic crop growth simultion model tht simultes dily wter blnce, soil tempertures, nd plnt wter deficits in response to wether inputs, soil chrcteristics, plnt growth chrcteristics nd crop mngement prctices (Boote et l., 1998). This model hs been successfully used to simulte soil wter blnce nd frction of extrctble soil wter (FESW), which is strongly relted to physiologicl ctivity (Sinclir et l., 1987), for sndy soils in West Afric (Nb et l., 2004) ndindi(singh et l., 1994). CROPGRO-penut is prticulrly suited to predicting fltoxin s it grows cohorts of pods, llowing temporl effects on individul pods to be modelled nd ccumulted. If observed field vlues for infection nd contmintion cn be quntittively relted to simulted vlues of FESW or wter deficit from clibrted models, then these reltions could form the bsis of decisionsupport system to predict the occurrence or risk of fltoxin contmintion in penut. The overll im of the work reported here ws to exmine whether mesured A. flvus infection nd fltoxin concentrtion in the field in Niger, West Afric, could be predicted from simulted vlues of FESW, nd hence form the bsis of risk model. Wliyr et l. (2003) grew four penut cultivrs t different sowing dtes nd levels of irrigtion in ech of 4 yers t Sdore in Niger, West Afric nd mesured A. flvus infection, fltoxin concentrtion, nd pod yield. The objectives of this study were, therefore: (i) to exmine the effects of yer, sowing dte nd irrigtion tretment (giving 40 different environments ) on pod yield, A. flvus infection nd fltoxin concentrtion in susceptible penut cultivr, JL24 grown in the field; nd (ii) to quntify reltions between observed vlues of A. flvus infection nd fltoxin concentrtion with simulted soil moisture or drought stress (FESW). 2. Mterils nd methods Experiments were crried out t the ICRISAT Shelin Centre, Sdore, Niger ( N, E) between 1991 nd The soil t Sdore is clssified s Psmmentic Pleustlf (West et l., 1984) comprising 93% snd. The soil moisture holding cpcity in the root zone (top 60 cm) is 44 mm (West et l., 1984). Sdore hs short growing seson verging 90 dys with long-term ( ) nnul rinfll of 545 mm (Sivkumr et l., 1993). The experiments were situted within 500 m of the reserch sttion wether sttion. Four cultivrs were grown in ech experiment (described below nd see Wliyr et l. (2003b) for full detils) but only results from one cultivr, JL24, re presented here s the overll im ws estblish reltions between infection/ contmintion nd drought (FESW), rther thn genotypic differences in these reltions; lso genetic model coefficients for these genotypes were not vilble. JL24 is short durtion Spnish cultivr susceptible to Aspergillus infection nd fltoxin contmintion Experimentl design nd culturl prctices In 1991, the experimentl design ws rndomised complete block in split plot rrngement with three replictions. Four levels of irrigtion (7, 14, nd 21 dys intervls nd rinfed [no irrigtion]) were used s min plots. At ech irrigtion, 20 mm of wter ws pplied using sprinkler irrigtion. There were four dtes of sowing (sowing with the onset of rin, followed by sowing every 10 dys therefter) s subplots. In 1992, 1993 nd 1994 the sme experimentl design ws used except tht only two dtes of sowing (sowing with the onset of rin, nd sowing 15 dys lter) were used. The plot size ws m (seven rows of 5 m) with spcing of 50 cm between rows nd 10 cm within the row (20 plnts m 2 ). Irrigtion tretments were buffered by 5 m strip. Before plnting, fields were prepred using n niml drwn plough nd brodcst with 40 kg h 1 of P 2 O 5.At plnting seeds were treted with Thiorl (25% heptchlore nd 25% Thirm) t the rte of 3 g kg 1 of seed. Seeds were hnd plnted. During the cropping seson one to three hndweedings were crried out using locl implements. In this environment groundnut experiments re usully treted with crbofurn to control nemtodes, which cuse vrible growth (Shrm et l., 1992; Wliyr et l., 1992). However, crbofurn ws not pplied in these experiments in cse it ffected A. flvus. Plnts were hnd hrvested t full mturity ( d). All the pods (mture nd immture) were removed from plnts nd immeditely brought to the crop-work re where they were dried in mesh trys t mbient ir tempertures of 30 to 35 8C. Under these conditions pods

3 22 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) dry to <10% kernel moisture content in 3 4 dys, voiding further fltoxin contmintion A. flvus nd fltoxin determintion A rndom smple of 300 pods were hnd shelled, out of which rndom sub-smple of 100 seeds ws tested in the lbortory to ssy for percent infection by Aspergillus (Wliyr nd Zmbettkis, 1979). More thn 90% of the soil fungl popultion ws A. flvus, nd other species (e.g. A. niger, A. prsiticus, Penicillium spp., Rhizopus spp.) were only present occsionlly. In brief, seeds were surfce sterilized by soking for 3 min in 0.1% queous solution of mercuric chloride, nd were rinsed three times with sterile distilled wter nd plced on filter pper in 10 cm dimeter sterile Petri dishes t 25 8C. To mintin high humidity, 1 to Tble 1 Rinfll between sowing nd hrvest, irrigtion pplied, clculted evportion, nd clculted frction extrctble soil wter (FESW) between flowering nd hrvest (FL to H), nd in the 25 dys before hrvest (H-25 dys) in experiments conducted between 1991 nd 1994 t the Shelin Centre, Sdore, Niger Sowing dte Irrigtion tretment Rinfll (mm) Irrigtion pplied (mm) Evportion (mm) FESW Fl to H H-25 dys dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed dys dys dys Rinfed

4 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) ml of distilled wter ws dded every dy during the first 5 dys. After 7 dys, the number of seeds contminted by Aspergillus ws counted. For ech tretment in 1992 nd 1993 fltoxin content ws mesured using n enzyme linked immuno-sorbent ssy (ELISA: Trnsi Society, Frnce) technique (Wliyr et l., 1994) in bulk smple from the three replictions. HPLC ws used to verify ELISA dt. In 1994, fltoxin content ws mesured in ech replicte. Afltoxin content ws not mesured in For ech nlysis, 100 g of seed ws rndomly picked nd ground in mill. A 20 g subsmple ws then extrcted in n queous methnol solution (80% v/v). Into this sub-smple, 60 ml of methnol solution ws dded. The smple ws then homogenized t high speed for 3 min nd filtered using Whtmn No. 1 filter. To determine fltoxin concentrtion from ech dilution (1:15, 1:75 nd 1:375), 50 ml of diluted extrcts were plced in duplictes into the wells. The opticl density ws red t wvelength of 450 nm with the id of micro-titrtion plte reder. Anlysis of vrince ws crried out for ech yer seprtely using rw dt (pod yield nd fltoxin) or ngulr trnsformed vlues (percentge infection) using Genstt 5 (Genstt 5 Committee, 1987). Pod yield dt ws firly vrible, nd originl replicte dt ws re-checked to confirm vlues, resulting in missing vlues being substituted for observed vlues in four plots Prediction of soil wter blnce CROPGRO-penut model ws clibrted using genetic coefficients for cv , short durtion Spnish type similr to JL24, using the observed experimentl nd site (soil chrcteristics nd wether) dt to simulte totl dry weight nd pod yield using procedures described in Boote et l. (1998) nd Hunt nd Boote (1998). The drined upper nd lower limits were nd cm 3 cm 3, respectively, nd the soil depth ws 0.6 m, giving 44 mm vilble wter. Key prmeters include the cultivr genetic coefficients for phenology (timing of vegettive nd reproductive stges), growth, pod ddition rte nd pod yield. Dily rinfll, ir nd soil temperture, rdition nd pn evportion were obtined from the wether sttion t Sdore. The model ws clibrted on the whole dt set to give the best prediction of phenology nd pod yield. Once the model ws clibrted, the verge frction of extrctble soil wter (FESW) in the root zone between flowering nd hrvest, or in the lst dys of the growing seson, in ech of the 40 environments ws clculted using the simulted dily soil wter content nd vilble wter content. Rtes of chnge in FESW were lso clculted, but s durtions from flowering to hrvest were mostly similr, nd irrigtion ws pplied t 7 21 dys intervls, this pproch did not improve predictions. Fig. 1. Decdl vlues of totl rinfll (brs) nd evportion (long-dshed line), nd verge ir (solid line) nd soil (dotted line) temperture t Sdore, Niger between 1991 nd Arrows show plnting dtes in ech yer.

5 24 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) Tble 2 Effect of sowing dte nd irrigtion tretment on observed dys to 50% flowering, number of plnts t hrvest, pod yield, A. flvus infection (trnsformed vlues in prenthesis) nd fltoxin concentrtion in cv. JL24 during Sowing dte Irrigtion tretment Dys to 50% flowering No. plnts t hrvest (m 2 ) Pod yield (kg h 1 ) %A. flvus (rcsine%) dys (30) 14 dys (35) 21 dys (39) Rinfed (46) 2 7 dys (36) 14 dys (41) 21 dys (44) Rinfed (51) 3 7 dys (40) 14 dys (45) 21 dys (47) Rinfed (55) 4 7 dys (46) 14 dys (50) 21 dys (54) Rinfed (62) SED (9, 24 d.f.) b (3.3) dys (26) dys (29) dys (35) 111 Rinfed (43) dys (33) dys (42) dys (51) 149 Rinfed (64) 197 SED (3, 8 d.f.) (1.5) c dys (28) dys (32) dys (35) 97 Rinfed (40) dys (38) dys (40) dys (46) 107 Rinfed (50) 132 SED (3, 8 d.f.) (0.8) c dys (27) dys (27) dys (28) 38 Rinfed (28) dys (32) dys (35) dys (40) 59 Rinfed (49) 208 SED (3, 8 d.f.) (0.7) 5.8 Not nlysed. b SED: stndrd error of the difference. c Unreplicted bulk smple. Afltoxin (mg kg 1 )

6 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) Results 3.1. Wether Totl rinfll during the experimentl period between 1991 nd 1994 rnged from 500 to 608 mm (Tble 1, Fig. 1), typicl vlues for Sdore in Niger (Sivkumr et l., 1993). Within individul sowing dte yer combintions, rinfll vried from 225 to 608 mm nd pn evportion from 455 to 705 mm. Under rinfed conditions pn evportion exceeded rinfll by >100% in some yers nd only in the first sowing dte (S1) in 1994 did rinfll exceed evportion. Therefore, in some sowing dte yer combintions frequent irrigtion ment tht excess wter my hve been pplied. Men dily ir nd soil temperture during pod-filling verged nd C, respectively, generlly incresing towrds the end of the seson s rinfll declined (Fig. 1). Environmentl conditions were therefore well within the rnge likely to fvour fltoxin concentrtion Flowering time, stnd counts nd pod yield JL24 flowered dys fter sowing in most experiments nd, with the exception of 1991, irrigtion tretments hd little effect on flowering time (Tble 2). In 1991, flowering times were s lte s 38 dys, but these delys were not systemticlly relted to irrigtion tretment or sowing dte. All experiments were hrvested round dys fter sowing (men dys) except for the third nd fourth sowing dte in 1991 (75 dys) nd the first sowing in 1992 (117 dys). Therefore, durtions from flowering to hrvest were similr, between 65 nd 70 dys. Experiments were estblished t 20 plnts m 2, but only t the first sowing dte in 1991 ws finl plnt snd close to this vlue (Tble 2). Plnt stnds were generlly <10 m 2 nd in some cses s low s 2.4 plnts m 2. Clerly drought, nd probbly nemtodes (Shrm et l., 1992; Wliyr et l., 1992) hd substntil effect on stnd estblishment. However, there ws no reltion (r 2 = 0.13) between pod yield nd stnd count. There were significnt effects of sowing dte on pod yield in ll yers nd significnt effects of irrigtion frequency in 1991 only (Tble 3). There were no significnt sowing dte irrigtion interctions. Pod yields were quite vrible, with rinfed plot yields often exceeding tht of plots receiving supplementry irrigtion. Pod yield vried with yer nd sowing dte, from 1315 kg h 1 t the first sowing dte (S1) in 1991 down to 53 kg h 1 t S2 in 1994 (Tble 3). Delyed sowing lwys reduced pod yield but there ws no consistent effect of irrigtion tretment on pod yield. The model predicted phenology nd yields of the whole dt set resonbly well (Fig. 2; r 2 = 0.67, P < 0.001, n = 40), with root men squre devition (RMSD) of 244 kg h 1. The rinfed pod yield t S (circled in Fig. 2) ws much higher thn predicted nd without this point r 2 = Predicted yields for three irrigtion tretments t S1 nd S2 in 1991 were noticebly higher thn observed yields Aspergillus infection nd fltoxin concentrtion There were significnt effects of irrigtion nd sowing dte on Aspergillus infection in ll yers (Tble 3). There were lso significnt sowing dte irrigtion interctions in 1992 nd The percent infection with Aspergillus (untrnsformed) rnged from 19 to 81% (Tble 2). Generlly, infection ws higher in 1991 nd lower in 1994, nd it incresed with lte sowing. For exmple, in 1991 men percent infection ws 37, 46, 53 nd 63 in S1 to S4, respectively. Likewise, infection incresed s the irrigtion frequency declined from 7-dy intervls to none (rinfed). For exmple, in S1 in 1991, infection ws 26, 33, 39 nd 51% t 7, 14 nd 21 dys intervls, nd rinfed, respectively. Afltoxin concentrtion ws not mesured in 1991 but between 1992 nd 1994 vlues rnged from 34 to 208 mg kg 1. In 1994, the only yer in which replicte vlues were nlysed, there were significnt effects of sowing dte, irrigtion nd their interction (Tble 3). Afltoxin concentrtion ws ffected by yer, sowing dte nd irrigtion tretment in similr mnner to Aspergillus nd there ws good reltion (r 2 = 0.71, P < 0.001, n = 24) Tble 3 Men sums of squres for replicte (Rep.), irrigtion nd sowing dte (Dte) effects on pod yield, percentge infection with Aspergillus (%A. flvus, ngulr trnsformed) nd fltoxin (1994 only) in cv. JL24 in d.f. Pod yield %A. flvus d.f. Pod yield %A. flvus Pod yield %A. flvus Pod yield %A. flvus Afltoxin Rep Irrigtion *** 516 ** *** *** *** 9966 *** Residul <1 86 Dte *** 526 *** ** 1228 *** ** 596 *** *** 807 *** *** Dte irrigtion < * *** 9808 *** Residul Totl * Significnce t P < ** Significnce t P < *** Significnce t P <

7 26 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) Fig. 2. Reltion between simulted nd observed pod yields of cv. JL 24 with CROPGRO-penut model cross ll sowing dtes nd irrigtion tretments during 4 yers (1991 through 1994): Y = X (r 2 = 0.67; P < 0.001; n = 40). Key to symbols:, 1991;, 1992; &, 1993;, Fig. 4. Reltion between observed pod yield nd simulted crop wter use cross ll sowing dtes nd irrigtion tretments during 4 yers (1991 through 1994): Y = X (r 2 = 0.62; P < 0.001; n = 40). Key to symbols:, 1991;, 1992; &, 1993;, between fltoxin concentrtion nd percent infection (Fig. 3) Pod yield, crop wter use nd FESW Simulted crop wter use vried from 193 mm t S1 in 1991 to only 44 mm t S4 in 1991 nd S2 in As proportion of totl wter use (plnt nd soil evportion, deep dringe nd runoff), these vlues represented between 34 nd <10% of totl wter use. Crop wter use ws noticebly higher t S1 nd S2 in 1991 (>100 mm) thn in other yers nd sowing dtes (ll <100 mm). Rinfll ws well distributed in 1991 (Fig. 1) nd erly sowings suffered no periods of prolonged drought nor periods of excessive rinfll which would hve checked plnt growth nd hence limited crop wter use. Across yers, sowing dtes nd irrigtion tretments there ws good reltion (r 2 = 0.62, P < 0.001, n = 40) between pod yield nd simulted crop wter use (r 2 = 0.75 without rinfed S2 in 1992, circled point in Fig. 4), though s noted previously pod yields were lower thn predicted in some tretments (e.g. S1 in 1991). The simulted frction of extrctble soil wter (FESW) between flowering nd hrvest rnged from 0.86 to 0.27 (Tble 1). In the lst 25 dys of the seson vlues of FESW rnged from 0.86 to Across ll sowing dtes, FESW ws greter nd soil moisture conditions therefore more fvourble with more frequent irrigtion. However, in ll yers FESW ws lower with lter sowing. If stress is defined s FESW < 0.50, then most tretments experienced some degree of drought stress, prticulrly towrds the end of the seson, despite irrigtion. For exmple, t S1 in 1991, where decdl rinfll totls were between 20 nd 70 mm in ll Fig. 3. Reltion between observed fltoxin concentrtion nd Aspergillus infection cross ll sowing dtes nd irrigtion tretments during 3 yers (1992 through 1994): = X (r 2 = 0.71; P < 0.001; n = 24). Key to symbols:, 1992; &, 1993;, Fig. 5. Reltion between observed Aspergillus infection nd verge simulted frction of extrctble soil wter (FESW) between flowering (FL) nd hrvest (H) cross ll sowing dtes nd irrigtion tretments during 4 yers (1991 through 1994): Y = X (r 2 = 0.62; P < 0.001; n = 40). Key to symbols:, 1991;, 1992; &, 1993;, 1994.

8 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) Fig. 6. Reltion between observed fltoxin concentrtion nd verge simulted frction of extrctble soil wter (FESW) in the lst 25 dys of pod-filling (H-25 dys) cross ll sowing dtes nd irrigtion tretments during 3 yers (1992 through 1994): Y = X (r 2 = 0.54; P < 0.001; n = 24). Key to symbols:, 1992; &, 1993;, periods with no dry spells, FESW remined >0.6 nd there were only 5 dys where FSEW < 0.5. Therefore, t most only mild nd trnsient drought occurred t S1. In contrst, t S4 in 1991 decdl rinfll totls were between 0 nd 30 mm, there were 22 dys where FESW < 0.5 nd drought ws therefore severe Aspergillus infection, fltoxin concentrtion nd FESW The yer, sowing dte nd irrigtion tretments creted wide rnge of wter stress conditions (Tble 1), which were reflected in the low yields nd low simulted crop wter use. Vlues of percentge infection with A. flvus (ngulr trnsformed) were most strongly negtively relted to verge FESW between flowering nd hrvest (Fig. 5; r 2 = 0.62, P < 0.001, n = 40); reltions with FESW in the lst 40 or 25 dys of pod-filling ccounted for hlf the vrition of tht between flowering nd hrvest. Afltoxin concentrtion (in only) ws lso negtively relted to FESW (Fig. 6; r 2 = 0.54, P < 0.001, n = 24), though in contrst to A. flvus the gretest proportion of vrince ws ccounted for by FESW in the lst 25 dys of pod-filling. Thus, when wter stress during pod-filling ws severe, infection nd fltoxin concentrtion were high. 4. Discussion The rnge in rinfed pod yields, from 53 to 1315 kg h 1, observed cross this 4-yer field study is typicl for penuts in semi-rid to rid climtes (e.g. Ntre nd Willims, 1998), nd illustrtes the vrible, nd hrsh conditions under which smll-scle subsistence frmers lbour in countries such s Niger. A smll dely in plnting fter the first rins in ny given yer substntilly incresed the risk of drought nd hence reduced pod yield. Lter sowings my lso hve estblished less well becuse of de-nitrifiction fter the first rins. Indeed, in 1993 nd 1994 pod yields hrdly exceeded the mount of seed plnted, typiclly 100 kg h 1. Yield ws not relted to rinfll totls, with the lowest pod yields occurring in the wettest yer (1994), showing tht rinfll distribution nd evportive demnd is fr more importnt (Dncette nd Forest, 1986). Pod yields cross ll tretments in this study were vrible (men 306 kg h 1, RMSD 244 kg h 1 ) nd in number of yers pod yields were higher in rinfed thn irrigted plots, with pod yield t S1 in 1992 nomlously high. Simultions suggested tht irrigted pod yields should hve been higher thn those observed, prticulrly in Although stnd counts were low in most experiments, vrition in pod yield ws not strongly ssocited with stnd count within or cross yers, nd using stnd count s covrite did not reduce vribility in pod yield. Previous studies hve shown tht nemtodes cuse considerble vrition in groundnut growth t this site (Shrm et l., 1992; Wliyr et l., 1992). Penuts re lso sensitive to excess soil moisture nd frequent irrigtion my hve contributed to wter logging nd lower yields s well (Ibrhim et l., 2002) in some tretments/yers. As nemtodes were not controlled in these experiments, the usul prctice t this site, it is probbly tht the combintion of drought, high soil temperture, wter logging nd nemtodes cused vrible stnd counts nd growth. CROPGRO-penut simulted pod yields resonbly well, excluding rinfed S2 in Across ll yers nd sowings observed pod yields were brodly relted to simulted crop wter use (trnspirtion) nd the mounts of wter used were typicl of penuts growing in semi-rid environments (Azm-Ali et l., 1989; Dncette nd Forest, 1986). Idelly it would hve been useful to hve some soil moisture dt to verify these simultions, but CROPGRO models hve been widely tested nd verified, including in semi-rid, northern Ghn (Nb et l., 2004). Within sowing dtes simulted crop wter use often did not vry much nd FESW would pper to be much better discrimintor of stress. Mny crop simultion models use FESW (or frction of trnspirble soil wter, frction of vilble soil wter) s there is consistency in plnt responses cross wide of conditions (Sinclir et l., 1987) nd s such FESW is useful physiologicl (stress) index. Drought nd high soil temperture were common occurrences, especilly when sowing ws delyed, giving rise to idel conditions for infection nd fltoxin contmintion (Cole et l., 1989; Snders et l., 1993; Prmr et l., 1997; Mrin et l., 1998). In the experiments reported here infection ws widespred nd fltoxin ws found t concentrtions >30 mg kg 1 t ll tretments in when verge FESW in the lst 25 dys of podfilling ws between 0.09 nd 0.67 nd verge soil tempertures (t the nerly meteorologicl sttion) were between 31 nd 35 8C. Unfortuntely fltoxin ws not mesured in 1991 when vlues of FESW were generlly

9 28 P.Q. Crufurd et l. / Field Crops Reserch 98 (2006) higher nd there should therefore hve been less contmintion. Previous studies hve shown tht combintion of >20 dys stress t the end of the seson with soil tempertures of 29 to 31 8C results in fltoxin contmintion. This is ssocited with stress reducing kernel wter ctivity (K w ) or internl RH to vlues between 0.85 nd 0.95 (Dorner et l., 1989); when K w > 0.95 phytolexins prevent contmintion nd when K w < 0.85 A. flvus does not grow or produce toxin. In the experiments reported here stress durtions (FESW < 0.5) were sometimes s short s 8 dys. Nonetheless contmintion occurred. Given dequte inoculum, infection with Aspergillus nd contmintion with fltoxin cn occur within short period of time. For exmple, Diener nd Dvis (1967) reported the minimum time for fltoxin production under optiml conditions is bout 60 h. The A. flvus strin in Niger is lso highly toxigenic (Wliyr, unpublished). Thus >20 dys drought nd high soil temperture stress re probbly not necessry for contmintion s long s the physiologicl conditions determining K w re met in some pods principlly immture or dmged pods. So even <10 dys stress ws enough to cuse significnt fltoxin contmintion. Nonetheless, it is cler tht the longer nd more severe the stress, the greter re levels of infection nd contmintion. CROPGRO-penut model successfully estimted pod yields over the 40 environments used in this experiment, nd simulted crop wter use nd FESW ccount for high proportion of the observed vrition in pod yield, infection nd contmintion. Assuming tht soil tempertures re fvourble for A. flvus nd fltoxin production, i.e. round 30 8C, then men FESW from podding to hrvest or the lst 25 dys of pod-filling could be used to predict infection nd contmintion, respectively, given bsic crop dt (flowering, podding nd mturity dtes), gronomic dt (sowing dte, soil wter holding cpcity nd soil type) nd wether dt. Where soil tempertures re outside the optiml rnge then soil temperture will probbly be needed s model input s well. This is the first time tht we re wre of where field observtions hve been successfully modelled in West Afric. Ngeswr Ro et l. (2004) hve used similr pproch to model the risk of contmintion in Queenslnd, using the crop simultion model APSIM to count the number of stress dys, which is then relted to risk. These simple empiricl reltions provide the bsis for decisionsupport system (DSS) tht cn be used by pthologists nd other crop scientists to predict infection nd contmintion in the field in environments where fltoxin is serious problem. A good exmple of DSS is the DON-forecsting system in Cnd (Hooker et l., 2002). These support systems will llow res historiclly t high risk, s well s res potentilly t risk in the coming seson, to be trgeted for technology trnsfer, e.g. of possible meliorting prctices such s erlier hrvesting or even supplementry irrigtion if vilble, s well s the promotion of greter wreness of the helth risks of fltoxin. Ngeswr Ro et l. (2004) hve shown how frmers in Queenslnd cn mnge fltoxin given DSS. In conclusion, this study hs shown tht infection nd contmintion occurred in the field in Niger even when stress periods were short. Infection nd contmintion cn be predicted in penuts using the frction of extrctble soil wter when soil tempertures re not limiting fltoxin contmintion. These reltions cn form the bsis of decision-support system for fltoxin risk prediction. References Azizeh, H.A., Pettit, R.E., Smith, O.D., Tber, R.A., Rection of penut genotypes under drought stress to Aspergillus flvus nd A. prsiticus. Penut Sci. 16, Azm-Ali, S.N., Simmonds, L.P., Ngeswr Ro, R.C., Willims, J.H., Popultion, growth nd wter use of groundnut mintined on stored wter. Prt III. Dry mtter, wter use nd light interception. Exp. Agric. 25, Bht, R.V., Vsnthi, S., Food Sfety in Food Security nd Food Trde: Mycotoxin Food Sfety Risk in Developing Countries. FOCUS 10, Brief 3 of 17, September Interntionl Food Policy Reserch Institute, Wshington, DC, USA. Blnkenship, P.D., Cole, R.J., Snders, T.H., Hill, R.A., Effect of geocrposphere temperture on pre-hrvest coloniztion of droughtstressed penuts by Aspergillus flvus nd subsequent fltoxin concentrtion. Mycopthologi 85, Boote, K.J., Jones, J.W., Hoogenboom, G., Pickering, N.B., The CROPGRO model for grin legumes In: Tsuji, G., Hoogenboom, G., Thornton, P.K. (Eds.), Understnding Options for Agriculturl Production. Kluwer Acdemic Publishers, Dordrecht, The Netherlnds, pp Chllinor, A.J., Wheeler, T.R., Crufurd, P.Q., Slingo, J.M., Grimes, D.I.F., Design nd optimistion of lrge-re process-bsed model for nnul crops. Agric. Forest Meteorol. 124, Cole, R.J., Snders, T.J., Dorner, J.W., Blnkenship, P.D., Environmentl conditions required to induce pre-hrvest concentrtion in groundnut. Summry of six yers reserch. In: Proceedings of Interntionl Workshop on Afltoxin Concentrtion in Groundnut. Interntionl Crops Reserch Institute for the Semi-Arid Tropics, Ptncheru, Indi, 6 9 October, 1987, Cole, R.J., Snders, T.J., Hill, R.A., Blnkenship, P.D., Men geocrposphere tempertures tht induce prehrvest fltoxin concentrtion of penuts under drought stress. Mycopthologi 91, Dncette, C., Forest, F., Alimenttion en eu de l rchide en zone tropicle semi-ride. In: Proceedings of n Interntionl Symposium on Agrometeorology of Groundnut. ICRISAT Shelin Centre, Nimey, D Mello, J.P.F., Mycotoxins in cerel grins, nuts nd other plnt products. In: D Mello, J.P.F. (Ed.), Food nd Sfety: Contminnts nd Toxins. CABI, Wllingford, UK, pp Diener, U.L., Dvis, N.D., Limiting temperture nd reltive humidity for growth nd production of fltoxin nd free ftty cids by Aspergillus flvus in sterile penuts. J. Am. Oil Chem. Soc. 44, Dorner, J.W., Cole, R.J., Snders, T.H., Blnkenship, P.D., Interreltionship of kernel wter ctivity, soil temperture, mturity nd phytolexin production in pre-hrvest fltoxin concentrtion of drought-stressed penuts. Mycopthologi 105, Genstt 5 Committee, Genstt 5 Reference Mnul. Clrendon Press, Oxford. Gong, Y., Egl, S., Houns, A., Turner, P., Hll, A., Crdwell, K., Wild, C., Determinnts of fltoxin exposure in young children from Benin nd Togo West Afric: the criticl role of wening. Int. J. Epidemiol. 32,

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