Epiphytic growth and survival ofTilletiopsis pallescens, a potential biological control agent ofSphaerotheca fuliginea, on cucumber leawes

摘要

The influence of low (70) and high (90) relative humidity on epiphytic growth, development, and survival ofTilletiopsis pallescens, a ballistospore-forming yeast-like fungus, on cucumber leaves was investigated. In addition, survival of the fungus in the presence or absence of powdery mildew (Sphaerotheca fuliginea) colonies was determined. Growth and development were visualized by scanning electron microscopy of the leaf surface, and survival was quantified as colony-forming units recovered on a semiselective medium. Development ofT.pallescensfrom blastospores that were applied to healthy leaves at 70 relative humidity was limited to small colonies that grew adjacent to leaf veins 7 days after application. At 90 relative humidity, extensive hyphal networks had developed within 3 days of blastospore germination, and ballistospores were produced within 7 days. Growth and sporulation ofT.pallescenswere most extensive at the base and on the surface of leaf trichomas. In the presence ofS.fuliginea,T.pallescensmycelium developed adjacent to hyphae and conidiophores of the pathogen within 3 days at both 70 and 90 relative humidity. However, at 90 relative humidity, growth ofT.pallescenswas more extensive and ballistospores were produced within 5 days, and there was visible collapse of mildew hyphae. There was no evidence of penetration of the leaf or mildew hyphae byT.pallescens. Survival ofT.pallescenswas significantly (Pensp;=ensp;0.05) increased at 1 and 5 days postapplication at 70 relative humidity when blastospores were amended with 1 (v/v) canola oil ndash; lecithin. Survival at 90 relative humidity was also significantly increased with canola oil ndash; lecithin and by the presence ofS.fuliginea. The addition of liquid paraffin ndash; lecithin or liquid paraffin ndash; Tween had no effect on survival when compared to the control. The results from this study indicate that growth and survival ofT.pallescensare enhanced by high relative humidity and by the presence of powdery mildew, and canola oil ndash; lecithin amendment improved survival on the leaf surface at reduced ambient humidity.Key words: antagonism, biological control, powdery mildew, yeast.