Resistance of Various Classes of Grapes to the Bunch and Muscadine Grape Forms of Black Rot

Abstract

Abstract Eight or 9 commercial cultivars from each of 4 grape classes were inoculated with the black rot fungus (Guignardia bidwellii f. sp. euvitis and f. sp. muscadinii) of bunch and muscadine grapes, respectively. The 4 classes consisted of 3 bunch grape classes (Vitis vinifera L., American hybrids, and French hybrids) and 1 muscadine class (V. rotundifolia Michx). Resistance was determined by leaf and petiole infection ratings (0−4) and average leaf and petiole lesion size (mm). Inoculation with Guignardia bidwellii f. sp. euvitis resulted in significantly larger average leaf lesion size on Vitis vinifera than on American and French hybrids (4.3 vs. 3.5). American hybrids had significantly higher (3.3 vs 2.3) leaf disease rating than French hybrids. Vitis rotundifolia received significantly lower disease rating then the 3 bunch grapes classes (0.4 vs. 2.9). A hypersensitive reaction was observed on leaves of most V. rotundifolia cultivars. Inoculation with Guignardia bidwellii f. sp. muscadinii resulted in significant differences in leaf infection ratings between French and American hybrids (0.8 vs. 1.6) and between V. rotundifolia and the 3 bunch grape classes (3.1 vs. 1.2). There were significant pathogen form × grape class and pathogen form × cultivar within grape class interactions.