An Exobasidium Disease of Fruit and Leaves of Highbush Blueberry.

Abstract

Fruit of highbush blueberries (Vaccinum corymbosum L.) in southeastern North Carolina have been observed to suffer from sporadic outbreaks of distinct green spots on ripe fruit. Though edible, affected fruit are unsightly in market containers of fresh berries. In 1997, this disorder affected over 25% of the berries from a 5.7-ha field of the cv. Wolcott, rendering all fruit from this field unsaleable. In May 1998, the symptom was again observed in a planting of cv. Croatan. Samples were collected on the packing line from hand-harvested fruit and from the field. Sharply delineated green spots were observed on otherwise normal ripe fruit. The spots were 2 to 10 mm in diameter, circular or rarely irregular, not sunken or protruding, and often tinged with red. Affected tissues in ripe fruit extended 2 to 3 mm into the berry and were the texture and color of green, unripe fruit. Sparse white fungal growth was visible on the surface of some affected areas. In the field, spots were observed on fruit and leaves. Incidence was estimated at 5 and 1%, respectively. Spots on affected leaves were circular, 4 to 7 mm in diameter, light green, slightly thickened, and smooth on the upper surface; the underside was covered with dense white fungal growth. Microscopic examination of thinly sectioned berry and leaf tissue in water mounts revealed round basidia bearing 2 to 6 (most often 4) basidiospores (4.0 to 5.2 × 13 to 15 μm). Spores were consistent with descriptions of Exobasidium vaccinii (Fuckel) Woronin (1), being musiform to fusiform, slightly curved, and hyaline with a conspicuous hylar appendage, some with transverse septa. This is the first report of blueberry fruit infection by an Exobasidium species. Reference: (1) F. L. Caruso and D. C. Ramsdell, eds. 1995. Compendium of Blueberry and Cranberry Diseases. American Phytopathological Society, St. Paul, MN.