Seedling Disease of Muskmelon and Mixed Melons in California Caused by Fusarium equiseti

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Abstract
The cause of a seedling disease of Cucumis melo in the southern San Joaquin Valley, Kern County, California, was identified as Fusarium equiseti. Symptoms were reproducible on seedlings grown in soil at cool temperatures, 13-24 C (air temperature 27-33.degree. C), when soil surrounding the hypocotyl was allowed to dry. In soils fumigated with chloropicrin and reinfested with F. equiseti (104 macroconidia per gram of air-dried soil), 47% of C. melo seedlings damped-off and the survivors were 32% smaller in fresh weight compared with seedlings in fumigated noninfested soils 22 days after sowing. Osmotically priming seed to increase the velocity of emergence did not influence disease severity. The pathogen causes characteristic dry cortical rot on hypocotyls of many species in the Cucurbitaceae; all C. melo tested were severely affected, whereas all Cucurbita species were low to intermediate in resistance. The fungus was readily isolated from plants that did not show lesions. In field soils containing diseased seedlings, viable pathogen propagules ranged from 300 to 500/g of air-dried soil. The disease was not observed in more northern or central melon production areas of California.

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