Selection of Verticillium lecanii isolates with high potential for biocontrol of cucumber powdery mildew by means of components analysis at differenthumidity regimes

To identify characteristics for the selection of Verticillium lecanii isola tes with high potential for biocontrol of Sphaerotheca fuliginea under glas shouse conditions, an exploratory study was performed on the effect of wate r limitation on the development of 14 isolates. The conidial germination, g rowth and sporulation of isolates of V. lecanii were studied in a tritrophi c system on cucumber leaves and in a ditrophic system in Petri dishes. Thei r mycoparasitic ability was studied in S. fuliginea and Cladosporium clados porioides. All characteristics were clearly affected by humidity Four isola tes shelved good biocontrol potential. The performance of isolates on agar had less predictive value than on powdery mildew. The germination of isolat es of V. lecanii was lower and the mycelial growth faster on agar than on m ildewed leaves under corresponding humidity conditions. The results suggest that conditions in the phyllosphere differed from the set humidity in the surrounding air. A correlation was found between the lysis of C. cladospori oides growing in dual culture on agar with isolates of V. lecanii and the p arasitism of powdery mildew on detached, rooted leaves. C, cladosporioides might offer a suitable substrate for testing isolates of V. lecanii for myc oparasitic potential under various environmental conditions. Conidial germi nation, growth and sporulation had limited predictive value.