ROLE OF MONOSPORASCUS-CANNONBALLUS AND OTHER FUNGI IN A ROOT-ROT VINE DECLINE DISEASE OF MUSKMELON

A serious disease of muskmelon (Cucumis melo) caused widespread losses in the Lower Rio Grande Valley of Texas in 1986 and has persisted through the 1990 crop season. Primary symptoms on the roots include extensive browning and necrosis of the taproot and lateral roots, vascular discoloration, and discrete brown to red cortical lesions. Secondary vine decline symptoms are characterized by a dieback of older crown leaves, which advances distally to younger leaves as the plants approach maturity. Four fungi (Fusarium solani, Monosporascus cannonballus, Macrophomina phaseolina, and Stagonospora sp.) were frequently isolated from the roots of diseased plants. Pythium spp., Cephalosporium sp., and F. oxysporum were also encountered but at relatively low frequencies. In greenhouse pathogenicity tests, M. cannonballus and M. phaseolina caused moderate to high levels of root rot and significantly reduced root weights of inoculated muskmelon plants. M. cannonballus also caused significant reductions in vine length, formed dark perithecia on the roots, and was reisolated from diseased plants. This is the first report of M. cannonballus in Texas and only the second from the United States.