AN EXPANDED HOST-RANGE FOR THE MUSKMELON PATHOGEN MONOSPORASCUS-CANNONBALLUS

The pathogenicity of Monosporascus cannonballus to nine cucurbit and eight noncucurbit species was evaluated in the greenhouse by direct seeding into infested soil. Six of the cucurbit species were also tested under simulated field conditions in artificially infested microplots. In the greenhouse, M. cannonballus was isolated from 70-100% of the cucumber, muskmelon, and watermelon plants and from 33-70% of the bean, corn, sorghum, and sugar beet plants 8-9 wk after planting. Perithecia of the fungus were observed on the roots of all cucurbits tested but only rarely on roots of noncucurbits. Discrete brownish lesions, general light discoloration, and necrosis were characteristic symptoms of cucurbit root infection. Consistent reductions in top dry weight were observed in wheat, corn, and all the cucurbits tested. Screening of muskmelon (Cucumis melo) cultigens indicated tolerance to M. cannonballus in two breeding lines and several cultivars. In the microplots, typical vine decline symptoms were reproduced on muskmelon and watermelon 9 wk after planting. This report is the first to demonstrate pathogenicity of M. cannonballus to a wide range of cucurbits on the basis of greenhouse and microplot tests.