Light with an intensity of 1000 to 5000 lux inhibits the release of zoospores and the formation of zoosporangia of hop downy mildew (Peronoplasmopara humuli Miy. et Tak.). Zoosporangia release zoospores in water suspension both in light and darkness already after one hour. With increasing light intensity, however, the percentage of zoosporangia releasing zoospores decreases: after 6 hours 95% release zoospores in darkness and 72–84% in light. Light affects more sharply the onset of zoosporangia formation and the density of the mildew coating. In darkness the first zoosporangia form after 4 hours and a continuous dense coating after 12 hours. In light, depending on intensity, the first individual fruiting bodies and zoosporangia form after 6–22 hours, and their number remains nearly unchanged even after 30 hours of exposure. The inhibitory effect of light is only temporary, as the pathogen resumes forming dense, infective zoosporangia after 10–20 hours back in darkness under optimal conditions.
Krejzová R. (1973): The resistance of cultures and dried resting spores of three species of the genus Entomophthora to ajatin and the viability of their resting spores after long-term storage in the refrigerator. – Česká Mykologie 27(2): 107–111.
