Muscadine Grape Berry Rot Diseases in Mississippi: Disease Identification and Incidence

Abstract

Berry rot diseases of muscadine grapes were monitored throughout the 1991 and 1992 growing seasons on four cultivars (Doreen, Sterling, Carlos, and Cowart) at three locations in south Mississippi. The etiology and symptom development of each berry rot disease were studied. Disease incidence data were collected at 2-wk intervals during both growing seasons. Fruit diseases observed on berries included black rot (Guignardia 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 in Mississippi, followed closely by black rot. The incidence of Macrophoma rot and ripe rot was low. On leaves, the incidence of black rot was greatest during the middle and late growing seasons. On berries, black rot was most severe as berries approached full size. Cowart and Carlos cultivars were most susceptible to black rot. The incidence of bitter 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. The cultivar, Sterling, was most susceptible to bitter rot and russet, but was resistant to black rot. Russet was most severe on full-size berries. G. uvicola was always associated with the russet symptom, and it may be a type of resistance expression by some cultivars to early infection or colonization by this pathogen. Both Colletotrichum acutatum and C. gloeosporioides were identified as causal agents of ripe rot on muscadine grapes in Mississippi.