Effect of environmental factors on growth, pycnidial production and spore germination of Microsphaeropsis isolates with biocontrol potential against apple scab

The potential as biocontrol agents of the apple scab pathogen, Venturia inaequalis and the effect of environmental factors on growth, pycnidial production and spore germination of four isolates of Microsphaeropsis were examined on culture media and leaf discs. V. inaequalis ascospore production was reduced by 52, 77, 89 and 95% on leaf discs treated with the isolates IMI 294735, P176A, DAOM 198536 and P130A, respectively. For all isolates, optimum temperature for mycelial growth was 25 degreesC. More pycnidia were produced on culture media than on leaf discs. On culture media, optimum temperature was from 15 to 25 degrees, while on leaf discs it varied among isolates. Pycnidial production was inhibited by darkness and a minimum of 8 It light d(-1) was required. Spores of isolates P130A and DAOM 198536 germinated at temperatures above 15 degrees and at pH 4-5, as compared to 10 degrees and pH 4-8 for isolates P176A and IMI 294735. The best candidates were P130A and DAOM 198536 and optimum conditions for growth, pycnidial production and spore germination were temperatures between 20 and 25 degrees, pH approx. 4 and light.