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Effect of Culture Conditions on Conidia Formation by Elsinoë ampelina, the Causal Organism of Grapevine Anthracnose

Elsinoë ampelina, the causal organism of grapevine anthracnose, can be easily grown in culture, yet its sporulation is poor and unstable in culture. In this study, we sought the optimum conditions for a simple method to stably generate conidia. We first examined the optimum period of incubation for young colonies grown on potato dextrose agar (PDA) in water. The resultant number of conidia showed a logarithmic increase, which slowed at about 8 to 10 h. This suggests that 8 to 10 h of preculture would provide a sufficient number of conidia under the culture conditions used. A high negative correlation between colony density on PDA and the number of resultant conidia existed: colonies grown at >2.5 colonies per cm² produced few or no conidia, whereas those grown at <1.0 colony per cm² stably produced as many as 2.9 × 10⁶ conidia. The optimum condition for preculture was to incubate colonies grown for 6 days on PDA at a density of <1.0 colony per cm². The conidia obtained by our method were pathogenic on the grape cultivar Rizamat.