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

[摘要] ENGLISH ABSTRACT:The evaluation of fungicide efficacy in commercial vineyards can be influenced by thesporadic occurrence of Botrytis cinerea at various positions on vines, differences in bunchstructure during bunch development and the phenomenon that symptom expression in shootsand bunches is governed by the resistance reaction of the various shoot and bunch parts. Ithas been postulated that, following air and water dispersal, infection by solitary conidiashould playa prominent role in the epidemiology of B. cinerea on grapevine. The aim of thisstudy was to determine (i) infection and (ii) fungicide efficacy at specific sites on shoots ofvinelets 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 therecommended dosages with iprodione, pyrimethanil, cyprodinil/fludioxonil and fenhexamidor were left unsprayed. After 24 h the vinelets or bunches were dusted with dry conidia ofBotrytis 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. Vineletsand bunches of the one group were surface-sterilised, the others were left unsterile. Vineletsand bunches of one unsterile group were placed in dry chambers, kept for 14 days at 22°Cwith a 12 h photoperiod daily and monitored for symptom expression and the development ofB. cinerea. Vinelets and bunches of the sterile group, and from one unsterile group wereused for isolation. From each of these vinelets leaf blades, leaf petioles, shoots andinflorescences were removed. Sites used for isolation in bunch parts were rachises, lateralsand pedicels, and sites on berries were the pedicel-end, cheek and style-end. The differentparts and segments were placed in Petri dishes on Kerssies' B. cinerea selective medium, oron water agar medium supplemented with paraquat and incubated for 14 days at 22°C with a12 h photoperiod daily. Infection and fungicide efficacy was determined by observing intactvinelets and bunches for symptom expression, and by estimating the amount of B. cinerea atthe 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 chambersduring the 2 wk observation period. The isolation and incubation studies showed that thedifferent 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 highamount of B. cinerea on unsprayed vinelets under the two sterility regimes, decay wassignificantly reduced by each fungicide on both cultivars. This was not the case for the otherparts, 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 thevarious bunch parts. At full bloom, the amount of B. cinerea in unsprayed bunches was highon the laterals and pedicels, but low on the embryos. Unsprayed intact bunches at full bloomwere highly susceptible to B. cinerea and developed symptoms of grey mould. Thefungicides 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 ofrachises, the amount of B. cinerea was at each growth stage drastically reduced by eachfungicide. In laterals, it was effectively reduced at pea size and bunch closure. However, atthese two sites, significant differences were found between the fungicides in efficacy atstages when the amount of B. cinerea was high. This study showed that if these fungicidesare applied properly to vine in commercial vineyards between budding and prebloom, duringflowering, and at bunch closure, they should effectively prevent infection and symptomexpression and thus the development of B. cinerea epiphytotics.

[发布机构] Stellenbosch University