MUSCADINE GRAPE BERRY ROT DISEASES IN MISSISSIPPI - DISEASE IDENTIFICATION AND INCIDENCE

Berry rot diseases of muscadine grapes were monitored throughout the 1 991 and 1992 growing seasons on four cultivars (Doreen, Sterling, Carl os, and Cowart) at three locations in south Mississippi. The etiology and symptom development of each berry rot disease were studied. Diseas e incidence data were collected at 2-wk intervals during both growing seasons. Fruit diseases observed on berries included black rot (Guigna rdia bidwellii f. muscadinii), bitter rot (Greeneria uvicola), russet (unknown etiology), Macrophoma rot (Botryosphaeria dothidea), and ripe rot (Colletotrichum sp.). Bitter rot was the most important disease i n Mississippi, followed closely by black rot. The incidence of Macroph oma rot and ripe rot was low. On leaves, the incidence of black rot wa s greatest during the middle and late growing seasons. On berries, bla ck rot was most severe as berries approached full size. Cowart and Car los cultivars were most susceptible to black rot. The incidence of bit ter rot on leaves was most severe on young leaves following bud break through the young berry stage, The incidence of bitter rot on berries was severe on small berries, especially those 1 to 3 mm in diameter. T he cultivar, Sterling, was most susceptible to bitter rot and russet, but was resistant to black rot. Russet was most severe on full-size be rries. G. uvicola was always associated with the russet symptom, and i t may be a type of resistance expression by some cultivars to early in fection or colonization by this pathogen. Both Colletotrichum acutatum and C. gloeosporioides were identified as causal agents of ripe rot o n muscadine grapes in Mississippi.