Infection by dry, airborne Botrytis cinerea conidia and fungicide efficacy on different parts of grape bunches and vinelets

Van Rooi, Cicelia (2002-03)

Thesis (MScAgric)--University of Stellenbosch, 2002.

Thesis

ENGLISH ABSTRACT: The evaluation of fungicide efficacy in commercial vineyards can be influenced by the sporadic occurrence of Botrytis cinerea at various positions on vines, differences in bunch structure during bunch development and the phenomenon that symptom expression in shoots and bunches is governed by the resistance reaction of the various shoot and bunch parts. It has been postulated that, following air and water dispersal, infection by solitary conidia should playa prominent role in the epidemiology of B. cinerea on grapevine. The aim of this study was to determine (i) infection and (ii) fungicide efficacy at specific sites on shoots of vinelets and bunches (table grape cultivar Dauphine and the wine grape cultivar Merlot) inoculated with dry, airborne conidia of B. cinerea. Vinelets, prepared from cuttings, and bunches obtained from the vineyards at full bloom, pea size, bunch closure, véraison and harvest stages, were sprayed in a spray chamber at the recommended dosages with iprodione, pyrimethanil, cyprodinil/fludioxonil and fenhexamid or were left unsprayed. After 24 h the vinelets or bunches were dusted with dry conidia of Botrytis cinerea in a settling tower and incubated for 24 h at a high relative humidity (±93%). Following incubation, both the vinelets or bunches were divided into three groups. Vinelets and bunches of the one group were surface-sterilised, the others were left unsterile. Vinelets and bunches of one unsterile group were placed in dry chambers, kept for 14 days at 22°C with a 12 h photoperiod daily and monitored for symptom expression and the development of B. cinerea. Vinelets and bunches of the sterile group, and from one unsterile group were used for isolation. From each of these vinelets leaf blades, leaf petioles, shoots and inflorescences were removed. Sites used for isolation in bunch parts were rachises, laterals and pedicels, and sites on berries were the pedicel-end, cheek and style-end. The different parts and segments were placed in Petri dishes on Kerssies' B. cinerea selective medium, or on water agar medium supplemented with paraquat and incubated for 14 days at 22°C with a 12 h photoperiod daily. Infection and fungicide efficacy was determined by observing intact vinelets and bunches for symptom expression, and by estimating the amount of B. cinerea at the various sites on the vinelets and bunches with isolation studies. No symptoms of B. cinerea decay developed on sprayed and unsprayed vinelets that were kept in dry chambers during the 2 wk observation period. The isolation and incubation studies showed that the different fungicides were highly and nearly equally efficient in reducing superficial B. cinerea inoculum and latent infection. .In the case of leaf blades, which showed a high amount of B. cinerea on unsprayed vinelets under the two sterility regimes, decay was significantly reduced by each fungicide on both cultivars. This was not the case for the other parts, which yielded B. cinerea at low incidences under the two sterility regimes. The study with bunches showed that dry, airborne conidia, and the fungicide sprays, penetrated loose and tight clustered bunches from bloom to harvest and evenly landed on the various bunch parts. At full bloom, the amount of B. cinerea in unsprayed bunches was high on the laterals and pedicels, but low on the embryos. Unsprayed intact bunches at full bloom were highly susceptible to B. cinerea and developed symptoms of grey mould. The fungicides inhibited symptom expression at full bloom, but could not prevent infection. Unsprayed bunches inoculated at the other stages remained asymptomatic. The amount of B. cinerea was generally high in the rachises and laterals at pea size and bunch closure stages, and in the pedicel end of berries at harvest. Infection was constantly low in the berry cheek. The fungicides had a differential effect on infection at the various sites. In the case of rachises, the amount of B. cinerea was at each growth stage drastically reduced by each fungicide. In laterals, it was effectively reduced at pea size and bunch closure. However, at these two sites, significant differences were found between the fungicides in efficacy at stages when the amount of B. cinerea was high. This study showed that if these fungicides are applied properly to vine in commercial vineyards between budding and prebloom, during flowering, and at bunch closure, they should effectively prevent infection and symptom expression and thus the development of B. cinerea epiphytotics.

AFRIKAANSE OPSOMMING: INFEKSIE DEUR DROË, LUGGEDRAAGDE BOTRYTIS CINEREA KONIDIA EN DIE EFFEK VAN FUNGISlEDE OP VERSKILLENDE SETELS BINNE WINGERDTROSSE EN OP LOTE: Evaluering van fungisieddoeltreffendheid in kommersiële wingerde word beïnvloed deur die sporadiese voorkoms van Botrytis cinerea op verskeie posisies van wingerddele, verskille in trosstruktuur tydens trosontwikkeling, en die feit dat simptoomuitdrukking in lote en trosse deur die weerstandsaksie van die verskillende morfologiese dele van lote en trosse beheer word. In die natuur speel infeksie deur enkel konidia 'n prominente rol in die epidemiologie van B. cinerea van wingerd. Die doel van hierdie studie was om (i) infeksie en (ii) die effek van fungisiede op verskillende posisies op lote en trosse (tafeldruif kultivar Dauphine, wyndruif kultivar Merlot), wat met droë, luggedraagde konidia van B. cinerea geïnokuleer is, te bepaal. Lote, verkry vanaf steggies, en trosse versamel vanuit die wingerde tydens blom-, ertjiekorrel-, trostoemaak-, deurslaan- en oesstadium, is teen aanbevole dosisse met iprodione, pyrimethanil, cyprodinillfludioxonil of fenhexamid in 'n spuitkas bespuit, of is onbehandeld gelaat. Na 24 h is die lote en trosse met droë konidia van B. cinerea in 'n inokulasietoring geïnokuleer en daarna vir 24 h onder hoë humiditeit [±93% RH] geïnkubeer. Na inkubasie is die lote en trosse in drie groepe verdeel. Die een groep lote en trosse is oppervlakkig gesteriliseer om die patogeen op die oppervlakte te elimineer, en die ander twee groepe is onbehandeld gelaat. Die lote en trosse van een nie-steriele groep is vir 14 dae in droë voghokke by 22°C met 'n 12 uur daaglikse fotoperiode geplaas, en daagliks vir siekteuitdrukking en die ontwikkeling van B. cinerea gemonitor. Lote en trosse van die ander twee groepe is vir isolasiestudies gebruik. Vanaf elke loot is blaarskywe, blaarstele, internodes en ongeopende blomtrossies verwyder. Vanaftrosse is ragisse, laterale en korreisteie verwyder, en vanaf korrels is skilsegmente aangrensend aan die korrelsteel, die stempel-end, en die wang verwyder. Die dele en segmente is op B. cinerea selektiewe medium, en op paraquat medium in Petri bakkies geplaas en vir 14 dae by 22°C met 'n 12 uur daaglikse fotoperiode geïnkubeer. Infeksie en die fungisiedeffek is bepaal deur die intakte lote en trosse vir siekte- uitdrukking te monitor, en deur die hoeveelheid B. cinerea op verskeie posisies op lote en trosse te bepaal. Geen simptome het op enige posisie op bespuite en onbespuite lote, wat in droë hokke gehou is, ontwikkel nie. Die isolasie- en inkubasiestudies het getoon dat die verskillende fungisiede hoogs effektief op lote was, en inokulumvlakke van die patogeen doeltreffend verlaag het. In die geval van blaarskywe, wat hoë vlakke van B. cinerea op onbespuite steggies onder die twee steriliteitskondisies getoon het, is verrotting op beide kultivars betekenisvol deur die fungisiedes verlaag. Dit het egter nie vir die ander dele, waarop daar 'n lae voorkoms van B. cinerea onder die twee steriliteitskondisies was, gegeld me. Die studie met trosse het getoon dat droë, luggedraagde konidia en fungisiednewels beide oop en kompakte trosse vanaf blomstadium tot oes penetreer en eweredig op die verskillende dele land. Met blomstadium was die hoeveelheid B. cinerea in onbespuite trosse hoog op laterale en korrelstele, maar laag op die embrios. Onbespuite, intakte trosse was hoogs vatbaar vir B. cinerea by blomstadium en het simptome van vaalvrot ontwikkel. Die fungisiede het siekte-uitdrukking by blomstadium voorkom, maar kon nie infeksie voorkom me. Onbespuite trosse wat op ander stadia geïnokuleer is, het geen siekte-uitdrukking getoon me. Die hoeveelheid B. cinerea was hoër in die ragi, asook in laterale by ertjiekorrel- en trostoemaak stadium, en hoër in korreisteie by oesstadium. Infeksie was konstant laag in die korrelskil. Die fungisiede het 'n differensiële effek op infeksie by die verskillende posisies gehad. In die geval van ragi was die hoeveelheid B. cinerea drasties deur elke fungisied by alle groeistadia verlaag. In laterale was dit effektief by ertjiekorrel- en trostoemaakstadium verminder. By hierdie twee posisies waar die hoeveelheid B. cinerea hoog was, is daar egter betekenisvolle verskille in die doeltreffendheid van fungisiedes gevind. Hierdie studie toon dat as fungisiede behoorlik in kommersiële wingerde tussen botvorming en blomstadium, en tydens blom- en trostoemaakstadium toegedien word, infeksie en siekte-uitdrukking, en dus ook die epifitotiese ontwikkeling van B. cinerea, voorkom behoort te word.

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