CONTROL OF INFECTION AND SPORULATION OF BOTRYTIS-CINEREA ON BEAN AND TOMATO BY SAPROPHYTIC YEASTS

Saprophytic yeasts were screened for their ability to reduce the sporulation of Botrytis cinerea and the severity of gray mold. One isolate of Rhodotorula glutinis and two isolates of Cryptococcus albidus effectively controlled disease on bean and tomato plants. Their ability to reduce the germination of conidia and the severity of rot symptoms on detached leaves and to control the disease on whole plants at calculated concentrations of 750-7,500 cells per square centimeter under growth-room conditions was consistently as effective as the known biological control agent Trichoderma harzianum T39 (unformulated). Glucose and KH2PO4 (0.02 M each) were added to conidial suspensions of B. cinerea to enhance infection. The yeast isolates were effective at this low nutrient level. All isolates competed for nutrients with the germinating conidia of B. cinerea, but resistance induced in the host by live or dead yeast cells may also have been involved. Small amounts of compounds inhibitory to B. cinerea germination were detected on treated leaves. Establishment of yeast populations on healthy and Botrytis-infected leaves and flowers was investigated. Five days after application, population densities of yeasts reached 7-8 X 10(3) cfu/cm(2) of healthy bean and tomato leaves and increased 7.5- and 8.5-fold on infected leaves of the respective crops. Lesion expansion and sporulation of B. cinerea were reduced after its establishment on leaves.