The ecology of Botrytis cinerea on grape in the Western Cape Province

[摘要] ENGLISH ABSTRACT:Botrytis cinerea Pers.: Fr., a pathogen of grapevine (Vitis vinifera L.), moves mainlythrough conidia by air currents in vineyards which are deposited intermittently on thesurfaces of leaves, inflorescences and bunches. Little is known about the relationship betweenthe inoculum dosage in air and incidence of Botrytis bunch rot, and how the relationship isinfluenced by environmental and host factors. To better understand this relationship,information is needed on the period over which conidia have accumulated, the time they areable to survive and remain infectious, time of symptom expression in relation to conidiumarrival at the infection court and host surface wetness. The aims of this study were (i) toestimate the amount of viable B. cinerea occurring in air in vineyards, and at differentpositions on leaves, inflorescences and bunches of grape at different phenological stages, (ii)to determine the relationships between the number of B. cinerea colonies recorded on sporetraps placed in the bunch zone of vines and the incidence of B. cinerea recorded from thedifferent tissues, and (iii) to compare the efficacy of fenhexamid on leaves and inflorescencescarrying natural B. cinerea inoculum with those inoculated with dry, airborne conidia.Different techniques were used to detect viable Botrytis cinerea in air currents and onplant material obtained from table (cultivars Dauphine and Waltham Cross in Paarl- andWorcester-district) and wine grape (cultivars Chardonnay, Sauvignon Blanc and Merlot inStellenbosch- and Malmesbury district) vineyards in the Western Cape province during2001-02 and 2002-03. For four consecutive days during prebloorn, bloom, pea-size, bunchclosure, veraison and harvest, sets of Petri dishes with freshly prepared Kerssies' B. cinereaselective medium (spore traps) were left overnight in the bunch zone of vines. Plant materialwas collected from the vines on the fourth day. Leaves, infloresence and bunches weretreated with paraquat to terminate host resistance and to promote the development of thepathogen on the tissues. The B. cinerea inoculum dosage in air, and the incidence at whichthe pathogen was detected at various positions on leaves and in bunches normally differedbetween vineyards. However, the various tests revealed that the pathogen generally occurredin a consistent pattern in air in the bunch zone of vines, on leaves and in bunches from allvineyards. The inoculum dosage in air in the bunch zone of the vine was generally highestduring prebioom or during bloom, it decreased at pea size and mostly remained at a very lowlevel at the later growth stages. The estimations of viable B. cinerea residing naturally onleaves and in bunches, showed that their amounts depicted levels occurring in air in the bunchzone of the vine. Necrotic leaves occurring early season in vineyards were identified as animportant source of secondary inoculum for dispersal to the developing bunches. Latentinfections at the various positions in bunches were few at véraison and harvest. However, dueto the necrotrophic ability of the pathogen, extensive berry rot (due to berry-to-berry contact)and thus severe bunch rot developed from a single berry that become symptomatic at the baseof the pedicel/berry attachment zone. The B. cinerea occupation pattern explains whyBotrytis bunch rot develops mostly from the inner bunch and why disease managementstrategies should concentrate on the bloom to pre-bunch closure stage and on inhibiting B.cinerea development in the inner bunch during the early part of the season. Thus, toeffectively reduce B. cinerea in grapevine, preventative applications are recommended toreduce two primary infection events: (a) between budding and pre-bloom to counteractprimary leaf infection; (b) during late bloom or early pea size stage, to reduce the amount ofthe pathogen on leaves and infloresences and to prevent colonisation of floral debris. A thirdspray can be applied at bunch closure to reduce the amount of B. cinerea at various positionsof the inner bunch, especially for cultivars with tight bunches.The efficacy of fenhexamid on leaves and inflorescences carrying natural B. cinereainoculum was compared with those inoculated with dry, airborne conidia. Shoots wereobtained during late bloom from a vineyard (wine grape cultivar Merlot) in the Stellenboschregion. The shoots were divided into two main groups. One group of shoots was leftuninoculated, the other shoots were inoculated by dusting with dry B. cinerea conidia in asettling tower. Before inoculation, equal numbers of shoots in each main group was sprayedwith fenhexamid, or left unsprayed. Following inoculation and incubation, shoots of eachtreatment were divided in two equal groups. The one lot of shoots were rinsed in water. Theother lot of shoots were immersed in paraquat solution to terminate host resistance and topromote the development of the pathogen from the tissues. For both uninoculated andinoculated shoots, irrespective of fungicide treatment, leaves remained asymptomatic at boththe blade and petiole position for the water rinse treatment. No symptom of B. cinerea decaydeveloped at any of the positions on leaves from shoots sprayed with fenhexamid. Sprayingof shoots with fenhexamid completely suppressed B. cinerea infection and symptomexpression on both uninoculated and inoculated inflorescens. For inoculated shoots, B.cinerea developed from approximately 50% of the laterals in the water rinse treatment.However, inflorescences rinsed in water remained asymptomatic.The laboratory studies showed that fungicides, if applied properly to shoots and bunchesunder controlled conditions, effectively reduced the amount of B. cinerea at the variouspositions on leaves and inflorescence, and prevented infection and symptom expression atbloom. However, these goals are not achieved in vineyards where the fungicides are appliedby conventional spraying methods. Therefore, more work is needed to evaluate fungicideapplication techniques by conventional spraying methods for proper fungicide coverage, andthe reduction of B. cinerea in bunches.

[发布机构] Stellenbosch University