S DROBY¹, T ZAHAVI¹, L SCHENA², L COHEN¹, B WIESS¹, A DAUS¹, R BEN-ARIE¹, E CHALUTZ¹ and A IPPOLITO²

¹Dept. Postharvest Science, ARO, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel; ²Dip. Di Protezione Delle Piante Dalle Malattie, Universita Degli Studi Di Bari, Via Amendola, 165/a, 70126 Bari, Italy

Background and objectives
Table and wine grapes are considered as one of the major agricultural crops worldwide. The most important pre- and post-harvest diseases of grape bunches are caused by Botrytis cinerea, Aspergillus niger and Rhizopus stolonifer. At present, control of grape bunch decay depends largely on the use of chemical fungicides applied as pre-harvest sprays during berry development. However, the decreasing efficacy of many of the fungicides used, as well as risks associated with fungicide residues on the fruit, have highlighted the need for a more effective and safer alternative control measures.

Development of economically and environmentally sound control strategies of bunch decay using biocontrol agents is being pursued by several laboratories around the world. For the past 4 years we have been isolating and developing indigenous antagonistic yeasts effective against pathogens of grape bunch.

Results and discussion
Initially we have characterized epiphytic yeast populations on table and wine grapes using RAPD-PCR techniques to group the isolates which have similar banding patterns. Representatives of the various yeast groups were then selected and identified using classical identification procedures. Results showed that the vast majority of yeast populations on wine and table grapes consisted of Candida, Debaryomyces, Rhodotorola and Acremonium species. Biocontrol efficacy of many yeasts isolated during three successive seasons was evaluated using whole grape clusters and detached grape-berry assays. Among the yeasts tested, four promising yeast isolates (L277, A42, B11 and L47) were effective against B. cinerea, Aspergillus niger and Rhizopus stolonifer under laboratory conditions.

Efficacy of yeast isolates was also evaluated in large scale tests in the vineyard for the control of pre- and post-harvest decay of wine and table grapes. The antagonists were applied in the vineyard in weekly intervals starting the fourth week before harvest. Results of two field tests conducted in two successive years showed 50-70% reduction of incidence of Botrvtis and Aspergillus decay developed in the vineyard. In table grapes, the reduction in incidence of post-harvest Botrytis rot ranged from 30-50%. A population study performed to evaluate the survival of the yeast antagonists under field conditions indicated a successful colonization of grape-berry surface by the yeast antagonists. In addition, a synergistic effect was found between the antagonists and low doses of two fungicides commonly used for the control of bunch rot. This may facilitate the development of an IPM approach based on either the combination of yeast antagonists and low doses of fungicides, or an alternation control program aimed at reducing the number of fungicide sprays.