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Comparative Epidemiology of Monosporascus Root Rot and Vine Decline in Muskmelon, Watermelon, and Grafted Watermelon Crops

Disease progression and soil population dynamics of Monosporascus cannonballus ascospores were studied and compared through the entire growing season in muskmelon, watermelon, and watermelon grafted onto Cucurbita rootstock crops. In muskmelon and watermelon, there was a decrease of ascospore counts in soil from transplanting until first symptoms of vine decline were observed. This decrease probably was related to ascospore germination and subsequent root infection. Later, there was a remarkable increase of ascospore counts in a parallel way to the quick development of vine decline symptoms, which lead to plant death. In these crops, root colonization adjusted to first-order linear equations and vine decline progression best correlated with exponential and logistic models. In contrast, there were no symptoms of vine decline on grafted watermelon. Furthermore, the isolation of M. cannonballus from Cucurbita roots was considerably lower, perithecia were never observed, and ascospore soil populations remained stable. These results suggest that disease control by grafting onto genus Cucurbita seems to be related primarily by the increased resistance of its root system to infection by M. canonballus, and provide further evidence of the use of grafting as a disease management measure for this disease.