Abstract. This research sought to obtain a superior yeast antagonist as a biological control agent of petal blight disease of dendrobium, to study the mechanism involved in biocontrol activity of yeasts and to study the effectiveness of yeast antagonists under field conditions. Five yeast isolates were investigated for their antagonistic activity in-vivo on detached petals, physiological characteristics in vitro and subsequently tested under field conditions. Among the yeasts tested, Cryptococcus terreus YSW1 was the most effective against petal blight of dendrobium caused by Curvularia pallescens. Antibiosis partly contributed to the biocontrol mechanism of C. terreus. The yeast was able to control petal blight disease under field conditions at the effective rate of 63-64 %. Optimum concentration for application of C. terreus was 10 cc L-1, or approximately 10 5 cfu L-1.
Key words: biological control, phyllosphere, tropical floriculture