The oomycetous pathogen, Phytophthora capsici Leonian, is capable of causing several disease syndromes in cucurbits, including crown rot, foliar blight, and fruit rot (Roberts et al., 2001; Zitter et al., 1996). Crown rot appears at the soil line as a dark brown, water-soaked lesion that quickly collapses the stem causing plant death. Foliar blight appears as rapidly expanding, water-soaked lesions on the leaves that eventually causes dieback of shoot tips, wilting, shoot rot, and plant death. Fruit rot appears as sunken, brown, water-soaked areas that are rapidly covered by white sporangial growth under moist environmental conditions.
The incidence of disease caused by P. capsici in cucurbit production areas of the United States has increased with reported yield loss as high as 100% (Hausbeck and Lamour, 2004; Tian and Babadoost, 2004). Given optimal environmental conditions, an entire cucurbit field may be destroyed by P. capsici in a matter of days (Roberts et al., 2001; Zitter et al., 1996). The increased occurrence of P. capsici has prompted research for improved fungicide control programs and an interest in breeding cucurbits for resistance to P. capsici (Babadoost, 2000; French-Monar et al., 2005; Hausbeck and Lamour, 2004; Keinath, 2007; McGrath, 2004; Seebold and Horten, 2003; Stevenson et al., 2000, 2001; Tian and Babadoost, 2004; Waldenmaier, 2004).
Cucurbita are considered to be one of the most morphologically variable genera in the plant kingdom (Robinson and Decker-Walters, 1999; Whitaker and Robinson, 1986). There are 22 wild and five cultivated species of Cucurbita. The cultivated species, grown around the world, include C. pepo, C. moschata, C. maxima, C. argyrosperma (formerly C. mixta), and C. ficifolia. Cucurbita cultivars are categorized as summer or winter squash. Summer squash is eaten immature when tender and seeds are small and soft. Winter squash is generally eaten when rind and seeds are fully mature. Summer squash cultivars belong to C. pepo, whereas winter squash cultivars may belong to C. pepo, C. maxima, C. moschata, or C. argyrosperma.
A search for sources of resistance within Cucurbita to the various syndromes of P. capsici had been performed at the University of Florida and included representatives from C. maxima, C. moschata, C. pepo, and three wild species, C. ecuadorensis, C. lundelliana, and C. okeechobeensis (Kabelka et al., 2007). From this screen, resistance to the crown rot syndrome of P. capsici was identified in the wild species, C. lundelliana, and C. okeechobeenesis subsp. okeechobeenesis. This resistance, derived from the two wild Cucurbita species, was introgressed through a series of hybridizations, self-pollinations, and single plant selections into a winter squash (C. moschata) background. One line, designated #394-1-27-12, was advanced to the F7 generation and is homozygous for P. capsici crown rot resistance. The objective of this study was to characterize the inheritance of resistance to crown rot caused by P. capsici within the Cucurbita breeding line #394-1-27-12.
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