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POSTERS: Population biology and genetics

Shifts in the blueberry stem blight pathogen complex and the appearance of fungicide resistant isolates
James Polashock - USDA ARS. Peter Oudemans- Rutgers University

Losses due to stem blight are increasing in many blueberry growing regions. Symptoms of the disease include drying of the leaves on one or more canes of an otherwise healthy bush. The disease can devastate young plantings and the mature bushes will die if the disease reaches the crown. Bushes are infected at wound sites and fungicides are largely ineffective in controlling the disease. The disease was thought to be caused by the fungus Botryosphaeria dothidiea, but recent data show that Neofusicoccum spp. and Lasiodiplodia spp. are also casual agents in some regions. Understanding the pathogen complex is the first step in developing effective control recommendations. Canes with typical stem blight symptoms were collected throughout the blueberry growing region in New Jersey. Fungi were isolated from the growing edge of the lesions and further characterized. Our data show that stem blight in New Jersey is caused primarily by Phomopsis vaccinii, a pathogen typically associated with twig blight in New Jersey, and Neofusicoccum spp. Virulence assays show that isolates from these genera are more virulent than isolates of B. dothidea. Other isolation and testing suggest that Pestalotiopsis spp. and Neopestalotiopsis spp. can also cause stem blight. Selected isolates were tested for fungicide resistance. Fungal growth was not inhibited by some of the fungicides tested; this may partly explain why incidence of stem blight is increasing.