5.2.64
BIOLOGICAL CONTROL OF BOTRYTIS BUNCH ROT OF GRAPES USING NATURALLY OCCURRING FUNGAL ANTAGONISTS

A STEWART1, A ANTONOV1, M TROUGHT1 and M WALTER2

1Department of Plant Science, PO Box 84, Lincoln University, Canterbury, NZ; 2The Horticulture & Food Research Institute of New Zealand Ltd, Canterbury Agriculture Science Centre, Lincoln, Canterbury, NZ

Background and objectives
In New Zealand, bunch rot disease of grapes, caused by Botrytis cinerea, may account for 20% or more fruit loss at mid season and up to complete loss of crop at harvest [1]. Conventional disease control is based upon repeated applications of fungicides. However, emerging fungicide resistance [2] has limited availability of fungicides, and the industry's move worldwide towards sustainability requires the development of new disease strategies such as the use of 'soft' fungicides and biological control. This programme investigates the potential of naturally occurring fungal saprophytes to inhibit the colonisation and sporulation of Botrytis on necrotic grape tissue as a means to reduce inoculum levels in the vineyard and subsequently the risk of bunch rot disease.

Results and conclusions
Microbial isolations were made from the phyllofructoplane of grapevines from three sites in the South Island, NZ. A total of 125 fungal isolates were obtained representing 8 genera (Alternaria, Aureobasidium, Cladosporium, Cryptococcus, Epicoccum, Gliocladium, Trichoderma and Ulocladium). These fungi were evaluated for antagonism towards Botrytis cinerea in a succession of laboratory bioassays using necrotic grape leaf tissue. The assays were designed to evaluate the test isolates' ability to suppress sporulation of the pathogen under different levels of water deficit and inoculum pressure. Based on a criterion of >90% suppression of Botrytis sporulation, six fungi (isolates of Epicoccum E21, E26, Trichoderma T13, T16 and Ulocladium U13, U16) were selected for further evaluation under field conditions. Two field trials were conducted over the 1996-97 growing season at three locations, two at Canterbury (Lincoln University and Giesen Vineyards) and one at Napier River Vineyard). Test isolates were applied as a spore suspension to necrotic grape leaf tissue 24 h after application of Botrytis conidia. Leaf discs were exposed to natural conditions in a grape canopy for periods of 10, 20 and 30 days.

At all sites and throughout all experiments, the six test fungi significantly reduced Botrytis sporulation compared to the control and performed equal to or better than the fungicide (iprodione) treatment. One Ulocladium isolate (U13) consistently suppressed Botrytis sporulation more effectively than the others. The best level of suppression by U13 was 90%, achieved under Botrytis conducive conditions at Napier. The three best isolates are currently being tested at the same locations for ability to suppress Botrytis sporulation on floral tissue and reduce Botrytis bunch rot incidence.

References
1. Nicholas P, Magarey P, Wachtel M, 1994. Diseases and Pests. Grape Production Series No.1, pp. 3-21.
2. Beever RE, Laracy EP, Pak HA, 1989. Plant Pathology 38, 427-437.