Dr. Claudia Probst discussed the relationship between host susceptibility, environment and timing in cherry powdery mildew disease development. She noted that sweet cherries are more susceptible to fruit infection as you get closer to harvest and that fungal spores on the fruit could survive for nearly two months.
Speaker: Dr. Claudia Probst, Postdoctoral Research Fellow in Plant Pathology. Coauthor: Dr. Gary Grove, Professor of Plant Pathology and Director. Affiliation: Washington State University Irrigated Agriculture Research and Extension Center, Prosser WA, 99350. Synopsis: Dr. Probst provides some taxonomic background on plant pathogenic fungi and notes that it is just one species that causes powdery mildew on cherry, Podosphaera clandestina. She explains the disease triangle and notes how this fungus needs a living, susceptible host and the right environmental conditions to cause disease. She defined ontogenic resistance as the ability of plants or plant parts to resist or tolerate disease as they age and mature. Dr. Probst noted that leaves are the biggest reservoir for season long inoculum production. In their research program, they posed several questions: Which developmental stage of cherry is most susceptible to infection? How many spores are needed to cause infection? Is there a relationship between blossom and fruit infection? What role does the environment play? From their laboratory and orchard inoculation experiments they learned that it doesn’t take many spores to cause significant disease at harvest. They also found that sweet cherry fruit had a reverse ontogenic resistance where immature fruit was more resistant to infection than mature fruit. Fruit were highly susceptible to infection near harvest. They also found that spores could remain viable (latent) on the surface of the fruit for nearly two months (56 days). They noted that bloom probably does not play an important role in the disease cycle and that the fungus may actually overwinter on the fruit.