Epiphytic growth and survival of Tilletiopsis pallescens, a potential biological control agent of Sphaerotheca fuliginea, on cucumber leaves
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| Authors: | Urquhart, EJ; Punja, ZK |
| Year: | 1997 |
| Journal: | Canadian Journal of Botany-Revue Canadienne de Botanique 75: 892-901 |
| Title: | Epiphytic growth and survival of Tilletiopsis pallescens, a potential biological control agent of Sphaerotheca fuliginea, on cucumber leaves |
| Abstract: | The influence of low (70%) and high (90%) relative humidity on epiphytic growth, development, and survival of Tilletiopsis 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 of T. pallescens from 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 of T. pallescens were most extensive at the base and on the surface of leaf trichomes. In the presence of S. fuliginea, T. pallescens mycelium 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 of T. pallescens was 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 by T. pallescens. Survival of T. pallescens was significantly (P = 0.05) increased at 1 and 5 days postapplication at 70% relative humidity when blastospores were amended with 1% (v/v) canola oil - lecithin. Survival at 90% relative humidity was also significantly increased with canola oil - lecithin and by the presence of S. fuliginea. The addition of liquid paraffin - lecithin or liquid paraffin - Tween had no effect on survival when compared to the control. The results from this study indicate that growth and survival of T. pallescens are enhanced by high relative humidity and by the presence of powdery mildew, and canola oil - lecithin amendment improved survival on the leaf surface at reduced ambient humidity. |
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