The Role of Petals in Development of Grey Mould in Strawberries

Transcription

1 The Role of Petls in Development of Grey Mould in Strwerries Pedro Boff 1, Joop de Krker 2, Mthijs Gerlgh 3 & Jürgen Köhl 3 1 Estção Experimentl de Ituporng, Empres de Pesquis Agropeuári e Extensão Rurl de Snt Ctrin-EPAGRI, Cx. Postl 121, 884- Ituporng, SC, Brsil, fx: (++51)(47) , e-mil: poff@epgri.rt-s.r; 2 Deprtment of Plnt Sienes, Wgeningen University, P.O. Box 43, 67 AK Wgeningen, The Netherlnds; 3 Plnt Reserh Interntionl B.V., P.O. Box 16, 67 AA Wgeningen, the Netherlnds, e-mil: j.kohl@plnt.wg-ur.nl Corresponding uthors: Pedro Boff nd Jürgen Köhl (Aepted for pulition on 7/11/2) BOFF, P., DE KRAKER, J., GERLAGH, M. & KÖHL, J. The role of petls in development of grey mould in strwerries. Fitoptologi Brsileir 28: Studies were onduted in nnul rops of strwerry (Frgri x nnss) (v. Elsnt to ssess the reltive importne of petls s n inoulum soure of grey mould, used y Botrytis inere nd to identify during whih period of flower nd fruit development the presene of petls hs signifint effet on development of grey mould on fruits. In 1998, the inidene of B. inere on flower prts ws ssessed, nd the symptoms of grey mould on fruits were hrterised with regrds to their strting point. The inidene of B. inere on petls ws 65-85% of those flowers tht hroured B. inere. The strting point of symptoms ws loted underneth the sepls in 65-85% of fruits with grey mould, nd petls were present t this site in out 5% of the ses. In 1999, four field experiments were onduted to ssess the effet of petl removl t different stges of flower nd fruit development on Importâni ds pétls no desenvolvimento do mofo-inzento do morngueiro Neste trlho ojetivou-se estudr importâni de prtes floris, espeilmente pétls, omo fonte de inóulo no desenvolvimento do mofo-inzento dos frutos do morngueiro (Frgri x nnss), usdo por Botrytis inere, e identifir os estágios de florção e frutifição nos quis presenç de pétls pode influir no umento d doenç. Preliminrmente, em 1998, foi vlid distriuição espil de B. inere ns flores e rterizou-se o tipo de sintom iniil do mofo-inzento nos frutos. Em pétls, o ptógeno esteve presente em 65 85% ds flores. Estmes form olonizdos em 85 1% dos sos. Sintoms iniiis do mofo-inzento estiverm lolizdos so s sépls em 65 85% dos sos, dos quis 5% presentrm presenç de pétls. Em 1999, onduzirm-se qutro experimentos pr estudr ABSTRACT RESUMO inidene of grey mould. The inidene of grey mould on fruits with petls retined till hrvest ws ir 55% more thn on fruits where petls were removed or hd dropped nturlly y the end of flowering, regrdless of plnting dte or inoulum level of B. inere. The inidene of grey mould ws hrdly different etween tretments where petls were removed t young flower stge, old flower stge, or green fruit stge. It is onluded tht petls re n effetive nd stle soure of inoulum for fruit infetion y B. inere. Considering the high proility tht retention of petls during fruit expnsion nd ripening results in fruit infetion, the elimintion of petls s n inoulum soure ppers worthwhile even when the inidene of petl retention on fruits is reltively low. Additionl key words: strwerries, Botrytis inere, flower, epidemiology, inoulum soure, phenology. o efeito d remoção de pétls n inidêni do mofo-inzento nos frutos. A inidêni do mofo-inzento em frutos, médi dos qutro experimentos, om um ou mis pétls presentes té olheit foi em torno de 55% mis do que nos frutos onde pétls form removids ou írm nturlmente no finl d florção. Não houve diferenç n inidêni do mofo-inzento entre os trtmentos om remoção de pétls té no estágio de flor-jovem, flor-velh e frutoverde. Conlui-se que pétls podem onstituir-se num fonte efetiv e estável de inóulo de B. inere, pz de usr infeção nos frutos. Considerndo um lt proilidde de permnêni de pétls durnte o estágio expnsão e mdureimento de frutos, remoção e/ou neutrlizção desss pétls omo fonte de inóulo, pode ontriuir sustnilmente n redução do mofo-inzento do morngueiro, mesmo que perentgem de retenção de pétls nos frutos té olheit for ix. INTRODUCTION Grey mould, used y Botrytis inere Pers. Ex. Fr. [teleomorph: Botryotini fukelin (de Bry) Whetzel], is 1 Prt of PhD thesis of the first uthor developed t Plnt Reserh Interntionl B.V., P.O. Box 16, 67 AA Wgeningen, the Netherlnds. the mjor use of fruit loss in strwerry (Frgri x nnss Duh.) (Reelo & Blrdin 1997; Hnok, 1999). Flower prts ply n importnt role in fruit infetion y B. inere. Powelson (196) nd Ppps & Jordn (1997) found tht strwerry fruit infetion were strongly redued if petls, stmens, nd lyes were removed fter fertilistion. Detiled studies y Powelson (196) nd Bristow et l. (1986) mde 76 Fitoptol. rs. 28(1), jn - fev 3

2 The role of petls in development of grey mould in strwerries ler tht infetion of the stmens n result in the estlishment of B. inere in the reeptle, wheres pistils, lyes (sepls) nd petls pper not to e diretly involved. The pthogen remins quiesent in the reeptle until ripening nd my then use fruit rot efore or fter hrvest (Powelson, 196; Jersh et l., 1989). The open flower stge ws shown to e the most suseptile to the estlishment of ltent infetions (Jrvis & Borek, 1968; Ppps & Jordn, 1997). Nowdys, the onventionl method of grey mould ontrol is y series of fungiide pplitions during the flowering period (Wilox & Seem, 1994; Ms, 1998). Aprt from their role in the estlishment of ltent infetions, flower prts of strwerry n lso e soure of inoulum for diret infetion of fruits. Wilkinson (1954) nd Jrvis (1962) oserved tht fruit infetions frequently strted from ded petls dhering to the surfe of the fruits, or trpped etween the fruit nd the lyx. While the role of ltent infetions estlished during flowering hs reeived onsiderle ttention, no detiled studies hve een onduted thus fr on the importne of petls in development of grey mould in strwerry. The ontriution of petls to fruit infetion will depend on their suseptiility to B. inere, nd on their fte fter flowering. Most petls strt to deth soon fter fertilistion, unlike stmens nd pistils tht remin tthed to the fruit. The reports y Wilkinson (1954) nd Jrvis (1962) re rther nedotl, nd do not provide suffiient ground to determine whether ontrol mesures should e trgeted t petls to eliminte this potentil inoulum soure, nd if so, wht the est timing of these ontrol mesures would e. In view of these questions, the reserh reported here imed to ssess the reltive importne of petls s n inoulum soure of grey mould in strwerry, nd to identify during whih period of flower nd fruit development the presene of petls hs signifint effet on development of grey mould. The speifi ojetives were (1) to understnd the distriution of B. inere mong petls nd other flower prts of strwerry, (2) to desrie symptom development on strwerry fruit with regrds to the strting point of infetion, nd (3) to investigte the effets of petl removl t different stges of flower nd fruit development on inidene of grey mould on ripe fruit. MATERIALS AND METHODS Inidene of Botrytis inere on flower prts The inidene of B. inere on petls, stmens, nd pistils ws ssessed in n nnul rop of strwerry v. Elsnt, ner Wgeningen, the Netherlnds. Smples were tken from four untreted plots nd from four plots where rop deris, exept flower prts, were removed twie weekly. The tretment plots were lid out in four rndomised loks. A smple of to 3 flowers, eh flower from different ritrrily hosen plnt, ws olleted per plot on July 21, August 5 nd 11, Only flowers with petls nd rown nthers were smpled. The flowers from eh smple were put into plsti oxes (22 m length x 14 m width x 5 m Fitoptol. rs. 28(1), jn - fev 3 height) with wet filter pper t the ottom nd inuted t 18 C for 12 dys in the drk. Petls, stmens, nd pistils were exmined for the presene of sporultion of B. inere with stereomirosope t 1-1 X mgnifition. Flower prts were onsidered olonised y B. inere when t lest one onidiophore ws present. Flowers were lssified ording to the presene of B. inere sporultion on the different flower prts. Seven lsses were distinguished: flowers with presene of B. inere sporultion t the sme time on petls, stmens nd pistils (pet_st_pis), on petls nd stmens (pet_st), only on petls (pet), only on stmens (st), on stmens nd pistils (st_pis), on petls nd pistils (pet_pis) or only on pistils (pis). The frequeny of eh lss, per smpling time, ws expressed s perentge of the totl numer of flowers with B. inere sporultion. Chrteristion of grey mould symptoms on strwerry fruits Symptom initition of grey mould ws determined on ll fruits hrvested from n untreted field of strwerry v. Elsnt ner Wgeningen, the Netherlnds, on August 15,, 24, 27, nd 3, Fruits with grey mould were lssified y hrterising the type nd strting point of symptoms s follows: () underneth sepls with petls present (undersep_withpet); () underneth sepls without petls present (undersep_nopet); () t the middle or tip of fruits (free_surf); (d) touhing infeted fruits (fruit_touh); (e) soil ontmintion (soil_touh); (f) mummified fruits (mummy); (g) overll sporultion nd unler strting point (unler); (h) physil surfe dmge (dmge) nd (i) pediel grey mould (stem_rot). The frequeny of eh speifi symptom ws expressed s perentge of the totl numer of fruits with grey mould, per hrvest dte. Petl mnipultion experiments Experimentl design, tretments nd rop mngement. Four experiments were rried out in smll field plots of strwerry v. Elsnt, on sndy soil ner Wgeningen, the Netherlnds, in Cold-stored trnsplnts kept t -2 C until the dy efore plnting, were trnsplnted on My 6 (Exp. 1 nd 2) nd June 19 (Exp. 3 nd 4). Eh experiment onsisted of 84 plnts in field plot of 4.5 x 4.7 m, omprising three doule-rows with three plnts per meter row length. Sping etween doule rows ws 1 m nd within doule rows.5 m. Experiments 1 nd 3 were onduted under nturl inoulum nd experiments 2 nd 4 under enhned inoulum pressure of B. inere. Enhned inoulum pressure of B. inere ws hieved y pling infeted strwerries inside the plots, from first white ud pperne until ripening. The infeted fruits, out two per plnt, were deposited in rows twie per week, in the middle of doule rows nd t the plot mrgins t 3 m distne from the strwerry plnts. The distne etween the fruits t first introdution ws 15 m nd dditionl fruits were pled in etween the previous ones, without removing ny old fruits. Experiments of nturl nd enhned B. inere inoulum pressure were seprted 77

3 P. Boff et l. y 1 m wide uffer strips of grss. Tretments were s follows: petls were removed with the help of foreps t young flower (YouFlo), old flower (OldFlo) or t green fruit (GreFru) stge; ll petls hd dropped nturlly during flowering (FreeFll) or t lest one petl remined tthed to the fruit till hrvest (Hrv); ontrol flowers were not mnipulted nor seleted for presene or sene of petls (Control). All tretments were replited three times, with the replites grouped in doule rows s loks. Per tretment, 4-6 suitle flowers or fruits (Hrv tretment) were ritrrily hosen in eh lok nd individully lelled y tthing tiny lel t the pediel. Mist irrigtion ws used to ensure wter supply for plnt development during dry periods. During flowering, irrigtion ws pplied every seond night from 21: till 6: h (5 min per 9 min period of time) to stimulte B. inere sporultion nd infetion. Pestiides were not pplied nd weeding ws done mnully. Spore lod in the ir. Spore lod in the ir ws monitored using Rotorod smplers Mod. (Smpling Tehnologies, Minnetonk, USA) with non-retrting olletor. Rotorods were positioned t.3 m height in the entre of the strwerry plots, nd 5 m outside the strwerry rops in the grss uffer. Runs were rried out on six dys (My 3 nd June 2, 8, 1, 15, nd 16, 1999) in experiments 1 nd 2 nd on seven dys (June 18, 23, nd 25 nd July 4, 7, 15, nd 22, 1999), in experiments 3 nd 4. Two runs per dy, exept on June 18, 1999 (one run), with 15 min durtion per run were rried out etween 9: nd 12: h, whih is the most likely period for spore relese of B. inere (Jrvis, 198). The spores of one rod per run were stined with otton lue (2 ml lti id + 4 ml glyerol ml otton lue t 1% + 2 ml distilled wter) nd onidi of B. inere were ounted on the 22 mm upper prt of rod using mirosope t x mgnifition. The numer of onidi of B. inere per ui meter of ir ws lulted per run nd s n verge per smpling dy. Flower nd fruit phenology. Lelled flowers of the first nd seond rnhes of four (Exp. 1) nd three (Exp. 3) ritrrily seleted plnts were monitored dily until fruit hrvest. The numer of petls per lelled flower from white ud pperne until hrvesting ws ounted. These petls were either still tthed to the reeptle or trpped etween the sepls nd the fruit. Development stges of flowers nd fruits were lssified s white ud (top of petls visile), open flower (fully reflexed petls until petl fll), green fruit (hene formtion), fruit expnsion (white fruits until fully red olour pperne) nd fruit ripening (red olour pperne until fully red fruit). Potentil sporultion of B. inere on petl. Removed petls, one per flower, of young flower (YouFlo), old flowers (OldFlo) nd green fruit (GreFru) tretments in ll experiments were pled on wter gr (1.5% of gr) in sterile plsti petri dishes ( 14 m) nd inuted for 14 dys, t 18 C in the drk. The perentge re with sporultion of B. inere ws estimted for eh petl using stereomirosope t x mgnifition nd expressed s potentil sporultion of B.inere on petls. Dt were verged per replite per tretment. Grey mould. Ripe, symptomless fruits nd disesed fruits were piked twie per week. Helthy fruits were lwys piked seprtely from disesed fruits to void ontmintion during hrvesting in view of post-hrvest evlutions. Helthy nd disesed fruits with non-speifi symptoms were individully put into squre plsti pots (5 m high) nd pots from the sme lok were pled side y side into plsti trys (5 m length x 3 m width x 7 m height) with wet filter pper on the ottom. Eh try ws seled within plsti g nd inuted 72 h t 18 C in the drk, to llow development of speifi symptoms. After inution, fruits were heked for the presene of B. inere sporultion. Inidene of grey mould ws expressed s perentge of the totl of symptomless nd disesed fruits, per tretment. Dt nlysis Sttistil nlysis of grey mould inidene ws performed y nlysis of vrine (ANOVA) followed y LSD-tests of ngulr-trnsformed vlues to seprte tretment mens (Snedeor & Cohrn, 1989) using the omputer pkge Genstt 5 version 4.1 (Genstt Committee, Algorithm Group In.). The miniml level of signifine ws tken s P=.5. Confidene intervls were lulted for the proportion of dys with higher ir lod of onidi of B. inere inside the strwerry field thn outside the field. The frequeny of strwerry fruits over grey mould symptom tegories nd the frequeny of B. inere over different flower prts were nlysed using ontingeny tles nd the Chi-squre test. Person s (r) oeffiient of orreltion ws lulted etween the inidene of grey mould in the ontrol nd the potentil sporultion re of B. inere on petls smpled t young flower, old flower, nd green fruit tretment stges. RESULTS Inidene of Botrytis inere on flower prts The frequeny distriution of B. inere presene on the different senesent flower prts ws not signifintly different over different flower prts etween untreted nd snittion plots nd lso the distriution of this frequeny ws not signifintly different mong smpling dtes within tretments (Figure 1). Petls nd stmens lone or in omintion, were responsile for 6-8% of B. inere inidene on flowers. Inidene of flowers with sporultion of B. inere on stmens lone or in omintion with other flower prts (85-1%) ws higher thn on petls lone or in omintion (65-85%), wheres this inidene on petls ws higher thn on pistils (-4%). Of ll possile omintions of flower prts infeted, B. inere never ourred on the omintion petl plus pistil, without 78 Fitoptol. rs. 28(1), jn - fev 3

4 The role of petls in development of grey mould in strwerries ourring on stmens s well. Symptom initition of grey mould on strwerry fruits The distriution of strwerry fruits over grey mould symptom tegories ws signifintly different mong hrvest dtes (χ 2 =148.6, df=32, P<.5). The tegory touhing infeted fruits nd the tegory under sepl without the presene of petls ontriuted most to this differene. The perentge of touhing infeted fruit tegory ws reltively high t the first hrvest, wheres the tegory under sepls without petls ws high t the lst hrvest. In 65-85% of the red strwerry fruits with grey mould, the strting point from where the symptoms hd spred ws loted underneth the sepls (Figure 2). Aout hlf of the fruits on whih grey mould hd strted underneth the sepls hd t lest one petl trpped in etween sepls nd fruit. Petls were ssoited with -4% of ll fruit rot. Grey mould rrely strted t the middle or on the tip of the fruit in sene of visile dmge ( %). Inidene of stem rot symptoms ws low (4-6%) nd these symptoms were only oserved t the end of the hrvesting period. Inidene of Botrytis inere (%) (6) 2(58) 3(41) 1(64) 2(52) 3(49) Untreted Snittion Smple (numer of flowers) pet_st_pis pet_st pet st st_pis pet_pis pis FIG. 1 - Inidene of Botrytis inere on senesent prts of strwerry (Frgri x nnss) flowers smpled on Jul 21 (1), Aug 5 (2) nd Aug 11 (3) 1998 from untreted plots (Untreted) nd plots where ll rop deris were removed, exept flower prts (Snittion). Eh olumn shows the proportion of flowers on whih B. inere ws present t the sme time on petls, stmens nd pistils (pet_st_pis), petls nd stmens (pet_st), only petls (pet), only stmens (st), stmens nd pistils (st_pis), petls nd pistils (pet_pis) or only on pistils (pis). Between rkets: numer of flowers with B. inere sporultion per smple. Petl mnipultion experiments Flower nd fruit phenology. Petls dropped mostly during the open flower stges (Figure 3). The retention of petls from the green fruit stge until hrvesting ws stle with on verge of.3 petls per flower. The frequeny of flowers with minimum of one petl followed the sme trend s the numer of petls per flower. During flowering (out six dys), 8% of ll flowers dropped ll petls nd the remining % retined t lest one petl until hrvest ( dys). Spore lod in the ir. The numer of onidi per m 3 of ir ws lwys higher inside field plots with enhned inoulum pressure of B. inere (> 1 m -3 ) thn inside field plots with nturl inoulum pressure (12-16 m -3 ) or outside the strwerry plots (1-14 m -3 ) (Tle 1). A higher onidil lod of B. inere inside the plot with nturl inoulum pressure s ompred to outside the plot ws found on four of six dys in experiment 1, nd on four of seven dys in experiment 3. The proportion of dys on whih more onidi were found inside the plot with nturl inoulum thn outside the plot ws not sttistilly different from.5, whih is the expeted Frequeny of symtom type (%) Aug(1) Aug(183) 24 Aug(119) Hrvest (totl numer of fruits) 27 Aug(187) undersep_withpet undersep_nopet free_surf fruit_touh soil_touh mummy unler dmge stem_rot 3 Aug(1) FIG. 2 - Frequeny of type nd strting point of grey mould symptoms used y Botrytis inere on strwerry (Frgri x nnss) fruits from untreted plnts evluted on August 15,, 24, 27, nd 3, Symptoms were lssified ording to type nd strting point s follows: under sepls with presene of petls (undersep_withpet) or without petls (undersep_nopet); t middle or tip of fruits (free_surf); touhing infeted fruits (fruit_touh); soil ontmintion (soil_touh); mummified fruits (mummy); generlised sporultion nd strting position (unler); surfe physil dmge (dmge) or pediel grey mould (stem_rot). Fitoptol. rs. 28(1), jn - fev 3 79

5 P. Boff et l. TABLE 1 - Air lod of onidi of Botrytis inere smpled y Rotorods during flowering of strwerry (Frgri x nnss) Numer of onidi per m 3 of ir per run Proportion of dys with ir lod inside field plot with Experiment Inside field plot with enhned inoulum pressure Inside field plot of nturl inoulum pressure Outside field plots Enhned inoulum > Nturl inoulum 1, , Rotorods run on six dys in experiments 1 nd 2, nd on seven dys in experiments 3 nd 4 Rotorods were loted 5 m from field plots. 95% onfidene intervl: (.33,.91) d 95% onfidene intervl: (.24,.87) Enhned inoulum > Outside field plots Nturl inoulum > Outside field plots d vlue when spore lods do not differ (Tle 1, 95% onfidene intervls). Potentil sporultion of B. inere on petls. The potentil sporultion re of B. inere ws higher on petls from experiments 2 nd 4 with n enhned inoulum pressure thn from experiments 1 nd 3 with nturl inoulum pressure (Figure 4). In generl, the potentil sporultion re of B. inere inresed with exposure time of petls to the inoulum present in the field. Petls smpled t green fruit stge lwys hd lrger potentil sporultion re of B. inere thn those smpled t young flower stges. Petls per flower (numer) Flowers with petl (%) White ud Open flower Green fruit Fruit expnsion Fruit ripening Dys fter white ud pperne 1st_exp. 1 2nd_exp. 1 1st_exp. 3 2nd_exp. 3 FIG. 3 - Petl retention of v. Elsnt from white ud pperne till hrvest. () numer of petls present per flower nd () perentge of flowers with t lest one petl per flower. Dt from flowers of first (1st_exp. 1, 69 flowers) or seond (2nd_exp. 1, 38 flowers) rnh of experiment 1, on Apr 16, 1999 nd from first (1st_exp. 3, 51 flowers) or seond (2nd_exp. 3, 43 flowers) rnh of experiment My 3, on 11, () () Grey mould. In ll experiments fruits with grey mould were found, ut the inidene ws onsiderly higher in experiment 2 nd 4 with the enhned inoulum pressure (Figure 5). Inidene of grey mould on fruits in the untreted ontrol ws 5-15% under nturl inoulum pressure, nd 25-55% under enhned inoulum pressure of B. inere. Between experiments, the inidene of grey mould in the ontrol ws positively orrelted (df=2, P<.5) with the potentil sporultion re of B. inere on petls smpled t young flower (r=.99), old flower (r=.95), nd green fruit stge (r=.98). When petls were present until hrvest, signifintly more grey mould ourred in omprison to ll other tretments, irrespetive the inoulum pressure of B. inere or the plnting dte (Figure 5). For exmple, the differene in grey mould inidene etween the tretments with petls present until hrvest nd with petls nturlly dropped during flowering, ws 51%, 51%, 54% nd 66% in experiment 1, 2, 3, nd 4, respetively. Inidene of grey mould on fruits with petls retined until hrvest ws higher Potentil sporultion re (%) Exp. 1 Exp. 2 Exp. 3 Exp. 4 Experiments Young flower Old flower Green fruit FIG. 4 - Potentil sporultion re of Botrytis inere on petls smpled from strwerry (Frgri x nnss) rops under nturl inoulum pressure (exp. 1 nd 3) nd enhned inoulum pressure (exp. 2 nd 4) of the pthogen. Petls smpled t young flower, old flower or green fruit stge were inuted in moist hmer t 18 C for 14 dys, in the drk. Columns with the sme letter in the sme experiment re not signifintly different (LSD-test; P=.5). Brs represent stndrd error of mens of three replites. 8 Fitoptol. rs. 28(1), jn - fev 3

6 The role of petls in development of grey mould in strwerries Grey mould (%) Grey mould (%) () () Experiment 3 Experiment 4 under enhned inoulum pressure (8-9%) thn under nturl inoulum pressure (55-6%) of B. inere. Removl of petls either t young open flower stge, old flower stge, or t green fruit stge hd no or hrdly ny differentil effet on grey mould of fruits. Among these three tretments, inidene of grey mould ws highest in the tretment where the petls hd een removed t the green fruit stge in three of four experiments, ut signifint differenes were only found in experiment 2 nd 3. Inidene of grey mould ws lowest on fruits tht originted from flowers of whih ll petls hd dropped nturlly during flowering in three of four experiments, ut did not differ signifintly from the inidene in the tretments where petls hd een removed t the young or old flower stge, exept in experiment 4. DISCUSSION Experiment 1 Experiment 2 YouFlo OldFlo FreeFll GreFru Hrv Control FIG. 5 - Inidene of grey mould of strwerry (Frgri x nnss) under nturl (exp. 1 nd 3) nd enhned (exp. 2 nd 4) inoulum pressure of Botrytis inere, in nnul strwerry rops trnsplnted on April 16, 1999 () nd on My 11, 1999 (). Tretments were: petls removed t young open flower (YouFlo), old flower (OldFlo) or green fruit (GreFru) stges; ll petls dropped nturlly during flowering (FreeFll) or petls remined tthed to the fruit till hrvest (Hrv); non-mnipulted flowers (Control). Columns of the sme experiment with the sme letter re not signifintly different (LSD-test; P=.5). Brs represent stndrd error of mens of three replites. Role of petls in strwerry grey mould Botrytis inere ws found on the stmens, petls, nd pistils of strwerry flowers (Figure 1). The inidene on petls ws somewht lower thn on stmens, ut lerly higher thn on pistils. Although the different flower prts differ d gretly in size nd numer, the differene in inidene my e relted to their degree of suseptiility to olonistion y B. inere. Bristow et l. (1986) found tht B. inere redily olonises nthers nd internl tissues of petls, wheres B. inere ould lso infet pistils, ut hyphl growth ws very slow nd restrited. The hrteristion of the type nd strting point of grey mould symptoms on strwerry fruits showed tht in the mjority of ses the infetion hd strted underneth the sepls (65-85% of disesed fruits, Figure 2). These results re very similr to those otined y Powelson (196), who found in survey of five strwerry fields tht 71-87% of the rotting fruits were infeted t the lyx end, nd suggested tht the rot originted from infeted stmens or sepls. However, our finding tht petls were present in out 5% of the ses where grey mould symptoms hd spred from underneth the sepls, indites tht petls lso n ply n importnt role in fruit infetion. Sepls hrdly senese until hrvest nd do not pper to e diretly involved in infetions t the stem end of fruits (Powelson, 196), ut they my ontriute indiretly y trpping petls, moisture, nd onidi of B. inere. The low inidene of grey mould symptoms strting t the middle or the tip of fruits, onfirms previous oservtions tht infetions of intt fruit from irorne onidi rrely our under field onditions (Jrvis, 1962). The experiments, in whih the role of petls ws investigted, demonstrted tht the retention of petls until hrvest gretly enhned the inidene of grey mould (Figure 5). The dditionl perentge of grey mould tht n e ttriuted to the presene of petls from flowering until hrvest ws 51-65%, lulted s the differene in grey mould inidene etween the tretment with petls present until hrvest nd the tretment in whih petls hd dropped nturlly y the end of flowering. This perentge ws remrkly onstnt ross the experiments, whih represented different levels of inoulum pressure nd, euse of the two trnsplnting times, lso different wether onditions. In ontrst, the degree of grey mould not ssoited with the presene of petls, for exmple in those tretments where the petls were removed during the flowering stges or where the petls hd dropped nturlly during flowering, ws muh more vrile ross the four experiments (Figure 5). It seems tht petls dhering to the fruit surfe re n effetive nd relile soure of fruit infetion y B. inere. These petls my t s sprophyti se for invding myelium, or filitte onidil infetions y trpping spores nd wter in etween the petl nd the fruit surfe. The ltter mehnism is proly of minor importne, euse the epidermis of strwerry fruit is not esily penetrted suessfully y onidi of B. inere, unless the fruits re fully ripe (Jersh et l., 1989), wheres infetion with myelil plugs is more effetive, even of hlf-ripe fruits (Jrvis & Borek, 1968). Kmoen et l. (1985) suggested tht the sprophyti se provided y dhering senesent petls lredy dethed t the se of the flower my funtion s protetion for the pthogen ginst inhiitors from the plnt, Fitoptol. rs. 28(1), jn - fev 3 81

7 P. Boff et l. nd llow the fungus to grow nd produe toxins or enzymes needed to overome plnt resistne. Myelil infetion from petls olonised y B. inere is lso proly less dependent upon wether onditions euse moisture requirements re less strit thn for onidil infetion. When petls re present throughout fruit development, the hne tht these petls will eventully e olonised y B. inere is high even when the inoulum pressure is reltively low. When does fruit infetion through the presene of petls our? The presene of petls up to the green fruit stge hd little or no influene on the inidene of grey mould (Figure 5). The period during whih petls my t s soure of fruit infetion y B. inere is minly etween the green fruit stge nd hrvest. This n e explined with the results from Powelson (196), who onluded tht petls do not ply role in the estlishment of ltent infetions in the reeptle during flowering, euse n sission lyer uses the petls to fll efore the fruit is invded. Regrding myelil or onidil infetion of intt fruit, severl studies hve shown tht intt young, green fruits re highly resistnt to B. inere, wheres the suseptiility of the fruits inreses towrds mturity (Jrvis & Borek, 1968; Jersh et l., 1989). In ddition to the greter suseptiility of ripening fruit, the effet of petl retention until hrvest n e explined y the long exposure time of the petls to Botrytis inoulum resulting in higher levels of petl olonistion (Figure 4). The long period of ontt etween the petls nd fruits lso enhnes the proility of n infetion event. Implitions for ontrol Wheres the retention of petls fter the green fruit stge enhnes the proility of fruit infetion onsiderly, the need to eliminte this inoulum soure will depend on how frequent petl retention is during fruit expnsion nd ripening. We oserved tht in strwerry v. Elsnt t lest one petl ws retined on out % of ll fruits (Figure 3). This is reltively low nd my explin why the role of petls hs not een studied in detil, in ontrst to the role of permnent flower prts (stmens, pistils, nd sepls). The redution in grey mould hieved y elimintion of petls, s ompred to non-intervention (untreted ontrol), ppers rther limited in our study. Only in the first two experiments signifint differenes were found etween the inidene of grey mould in the ontrol nd in ny of the tretments where petls hd een removed or dropped nturlly during flowering (Figure 5). However, it n e rgued tht the oserved level of redution in grey mould inidene ws in greement with the expeted level. Given tht in the ontrol tretment petls were present on % of the fruits, nd tht the presene of petls from flowering until hrvest on ll fruits enhnes the inidene of grey mould y out 5%, n dditionl 1% grey mould would e expeted in the ontrol tretment s ompred to tretments where petls were sent from the end of flowering onwrds. The oserved differene etween these tretments nd the ontrol ws on verge 7.5%. Thus, onsidering the high proility tht presene of petl results in fruit infetion, the elimintion of petls s n inoulum soure ppers worthwhile even when the inidene of petl retention on fruit is reltively low. Elimintion of petls s n inoulum soure of strwerry grey mould my e hieved y speifi mesures suh s seletion of ultivrs tht drop (lmost) ll petls or y physil removl of petls y lowing with ompressed ir. The ltter pproh hs some suess in vitiulture, where it is used to remove flower ps from the grpe (Vitis vinifer L.) lusters (Wolf et l., 1997), ut my e prolemti in strwerry where the flowering period is long with overlpping genertions of flowers. The onventionl wy to ontrol grey mould is y pplition of fungiides during flowering (Ms, 1998). These spry pplitions lso low off petls, whih my dditionlly ontriute to grey mould ontrol. Fungiides will redue olonistion of petls most effetively when pplied protetively, i.e. efore the rrivl of inoulum of B. inere, euse their post-infetion effet on petls is poor (Kmoen & Jmrt, 1975). The est timing of fungiide pplitions to ontrol this soure of inoulum will therefore proly e during flowering, lthough the petls give rise to fruit infetions muh lter during fruit development. Colonistion of petls y B. inere my lso e prevented or redued y sprophyti ompetitors suh s Glioldium roseum (Binier) nd Uloldium trum (Preuss) (Peng & Sutton, 1991; Köhl et l., 1995). For these ioontrol gents, timing of pplition my lso e ritil, euse the time dvntge of one speies over the other plys ruil role in ompetitive olonistion of sustrtes y B. inere nd the ntgonist (Kessel, 1999). Yet, suh ioontrol gents re promising mens to protet petls ginst B. inere, euse one suessfully estlished they my e le to exlude B. inere for the rest of the growing seson wheres fungiide pplition offers protetion for only limited period. ACKNOWLEDGEMENTS Funding for this reserh ws prtly provided y the Brzilin Government - Coordenção de Aperfeiçomento de Pessol de Nível Superior (CAPES; Pro. 2959/95-), whih inluded full sholrship to the first uthor. We lso knowledge the Europen Commission (BIOSPORSUPPRESS; FAIR3 CT ) for prtil finnil support for the reserh. We thnk Sski Burgers for sttistil ssistne. LITERATURE CITED BRISTOW, P.R., MCNICOL, R.J. & WILLIAMSON, B. Infetion of strwerry flowers y Botrytis inere nd its relevne to grey mould development. Annls of Applied Biology 19: HANCOCK, J.F. STRAWBERRIES. Wllingford, UK. CABI Pulishing JARVIS, W.R. The infetion of strwerry nd rsperry fruits y 82 Fitoptol. rs. 28(1), jn - fev 3

8 The role of petls in development of grey mould in strwerries Botrytis inere Fr. Annls of Applied Biology 5: JARVIS, W. R. Epidemiology. In: Coley-Smith, J.R., Verhoeff, K.& Jrvis, W. R. (Eds.) The Biology of Botrytis. London, UK. Ademi Press pp JARVIS, W.R. & BORECKA, H. The suseptiility of strwerry flowers to infetion y Botrytis inere Pers. ex Fr. Hortiulture Reserh 8: JERSCH, S., SCHERER, C., HUTH, G. & SCHLÖSSER, E. Pronthoynidins s sis for quiesene of Botrytis inere in immture strwerry fruits. Journl of Plnt Diseses nd Protetion 96: KAMOEN, O., JAMART, G., VAN VAERENBERGH, J. & GOUWY, P. Botrytis inere infetions on petls nd green leves. Mededelingen vn de Fulteit Lndouwwetenshppen Rijksuniversiteit Gent 5/3: KAMOEN, O. & JAMART, G. Further exmintion of the strwerry fruit rot ontrol y fungiides. At Botni Neerlndi 24: KESSEL, G.J.T. Biologil ontrol of Botrytis spp. y Uloldium trum, n eologil nlysis. (PhD thesis). Wgeningen, NL. Wgeningen University KÖHL, J., MOLHOEK, W.M.L., VAN DER PLAS, C.H. & FOKKEMA, N.J. Effet of Uloldium trum nd other ntgonists on sporultion of Botrytis inere on ded lily leves exposed to field onditions. Phytopthology 85: MAAS, J.L. Compendium of strwerry diseses. 2 nd ed. St. Pul, USA. Amerin Phytopthology Soiety PAPPAS, A.C. & JORDAN, V.W.L. Phenology of fruit growth nd suseptiility to grey mould (Botrytis inere) of strwerry, rsperry nd lkurrnt. Annls Institute Phytopthology Benki 18: PENG, G. & SUTTON, J.C. Evlution of miroorgnisms for ioontrol of Botrytis inere in strwerry. Cndin Journl of Plnt Pthology 13: POWELSON, R.L. Initition of strwerry fruit rot used y Botrytis inere. Phytopthology 5: REBELO, J.A. & BALARDIN, R.S. A ultur do morngueiro. Florinópolis, BR. Epgri SNEDECOR, G.W. & COCHRAN, W.G. Sttistil methods. 8 th ed. Iow, USA. Iow Stte University Press WILCOX, W.R. & SEEM, R.C. Reltionship etween strwerry gry mold inidene, environmentl vriles, nd fungiide pplitions during different periods of the fruiting seson. Phytopthology 84: WILKINSON, E.H. Oservtions on grey mould in strwerries. Plnt Pthology 3: WOLF, T.K., BAUDOIN, A.B.A.M. & MARTINEZ-OCHOA, N. Effet of florl deris removl from fruit lusters on otrytis unh rot of Chrdonny grpes. Vitis 36: Fitoptol. rs. 28(1), jn - fev 3 83