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

The pathogenicity of Monosporascus cannonballus to nine cucurbit and e ight noncucurbit species was evaluated in the greenhouse by direct see ding 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 cu cumber, 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, gener al light discoloration, and necrosis were characteristic symptoms of c ucurbit root infection. Consistent reductions in top dry weight were o bserved in wheat, corn, and all the cucurbits tested. Screening of mus kmelon (Cucumis melo) cultigens indicated tolerance to M. cannonballus in two breeding lines and several cultivars. In the microplots, typic al vine decline symptoms were reproduced on muskmelon and watermelon 9 wk after planting. This report is the first to demonstrate pathogenic ity of M. cannonballus to a wide range of cucurbits on the basis of gr eenhouse and microplot tests.