BIOLOGICAL-CONTROL OF POSTHARVEST DISEASES OF GRAPE, PEACH, AND APPLE WITH THE YEASTS KLOECKERA-APICULATA AND CANDIDA-GUILLIERMONDII

A yeast, strain 138 of Kloeckera apiculata, isolated from the surface of grapes, was evaluated for its activity in reducing postharvest decay of grape, peach, and apple fruits. In an artificial infection assay in which detached grapes were immersed in an aqueous suspension of yeast cells (5 x 10(8) cfu/ml) and spray-inoculated with 10(3) sporangiospores per milliliter of Rhizopus stolonifer, strain 138 reduced decay, whereas strain 87 (= US-7) of Candida guilliermondii did not. In an assay in which naturally infected fruits were immersed in yeast suspensions, both strains were effective in reducing postharvest decay of grapes caused by R. stolonifer; however, neither yeast was effective in reducing decay caused by Aspergillus niger. Three strains of K. apiculata obtained from other sources were compared to strain 138 and strain 87 for activity against Rhizopus rot of peach and gray mold of apple. Fruit wounds were pretreated with water-suspended yeast cells (10(8) cfu/ml) and inoculated with 10(3) sporangiospores of R. stolonifer per milliliter or 10(5) conidia of Botrytis cinerea per milliliter. Two of three strains of K. apiculata were as effective as strains 138 and 87 for the control of Rhizopus rot of peach. All strains were equally effective in reducing gray mold of apple. Control of gray mold and blue mold of apples and Rhizopus rot of peaches was enhanced when strain 138 was applied as an aqueous suspension (10(8) cfu/ml) in 2% CaCl2. This method did not reduce the incidence of brown rot of peach, caused by Monilinia fructicola; however, decreased lesion diameter was observed in fruit treated with yeast and CaCl2.