Physiology and Pathogenicity of the Cucurbit Black-rot Fungus^

The black-rot fungus, Myeosphaerella melonis (Pass.) Chiu and J. C. Walker, was first reported in France in 1891 on leaves of a Chinese variety of cucumber {CueUQyiis sativus L.) (¡^i) .^ It was recorded the next year from Delaware on vines of watermelon {Gitrullus vulgaris Sehr ad.), squash {Cucúrbita spp.), pumpkin {Cucúrbita pepo L.), muskmelon {Cucumis meló L.), and cucumber {3). Grossenbacher (7) studied the disease in the greenhouse in New York and reported that when vines were inoculated through wounds those of watermelon and muskmelon were very susceptible; those of pumpkin, squash, gourd {Lagenaria vulgaris Ser.), and dishcloth gourd {Luifa cylindrica Roem.) were only mildly affected, and those of cucumber and of bur cucumber {Cucumds anguria L.) were not infected. Weber {^4) later noted wilting of leaves of young cucumber seedlings in Florida. The disease has been reported on fruits of cucumber, muskmelon, squash, pumpkin, watermelon, chayóte {Sechiu/m edule Schwartz), balsam pear {Momordica charantia L.), and Chinese preserving melon {Benniiicasa hispida Cogn.) (Í7, 24^ 26). Black rot has been found more often in the southern than in the northern part of the United States. When, in 1945, vines of watermelon, muskmelon, and squash were found to be severely affected by the disease in southern Wisconsin, the present investigation was undertaken. A study of the morphology and variability of the pathogen was made and has been reported (4). A study of the physiology and pathogenicity of the fungus is reported in the present paper.