Strange Fruits: Gall and Leaf Spot Diseases Caused by Exobasidium Fungi
C. Benton Willis, Michael Goodnight, Jessica Velte, Marin T. Brewer, and Matthew E. Smith
Exobasidium fungi are plant pathogens that primarily infect plants in the Ericaceae family, including blueberries and azaleas. Their infections cause plant cells to proliferate (hyperplasia) and expand (hypertrophy). The fungi then use the increased surface area to produce spores. These changes manifest as symptoms on the host plant, varying by species of Exobasidium. The range of symptoms includes leaf and fruit spots, blisters, shoot proliferation (witches' broom), and galls. Infected plant tissues can also become swollen and distorted, as well as chlorotic (yellow) or discolored (reddish to pink). As this infected tissue matures, the surface becomes white and powdery from fungal spore production. Exobasidium fungi tend to cause symptoms on the plant during ideal weather conditions but can likely survive on the leaf surface or other available substrates year-round. Disease management includes chemical applications and cultural practices before the spores have the chance to mature.
