Digital microscopic analysis of conidiogenesis of powdery mildew pathogens isolated from melon leaves

Melons (Cucumis melo L.) grown hydroponically in a greenhouse were heavily infested with powdery mildew. We isolated powdery mildew pathogens from the melon leaves and identified the isolate as Podosphaera xanthii KMP-6N, based on morphological characteristics and sequences of ribosomal DNA internal transcribed spacer (rDNA-ITS) regions. Host ranges of KMP-6N were determined by estimating the infectivity or pathogenicity after inoculating the conidia onto multiple plant species. The fungi caused severe powdery mildew symptoms on Cucurbitaceae plants, producing scattered conidia on conidiophores. The goal of this study was to observe KMP-6N conidiogenesis on melon leaves. The pathogen formed completely catenated conidiophores approximately 24 h from conidiophore erection to release of mature conidia. Six conidia were produced on the conidiophores and only the conidia at the apex reached maturity. The cycles of conidial release were repeated on melon leaves 14 to 18 times, at approximately 6-h intervals. In the final stage, conidia were released without causing growth and septation of generative cells. Conidiophores produced an average of 36 conidia during a 90-h period. In our study, the modes of conidiogenesis, lifetime of conidiophores and productivity of conidia on a conidiophore were described for powdery mildew fungi.