Cucurbitaceae L. includes ≈120 genera and over 800 species. The family is predominantly of tropical origin with a few members that have been able to adapt to temperate climates. The genus Cucurbita consists of five cultivated species and 10 wild species, with perennials or annuals plants (Teppner, 2004).
The most important cultivated species in the genus Cucurbita are C. pepo L. ‘summer squash’, C. maxima Duchesne ‘winter squash’, and C. moschata ‘winter and crookneck squash’, and of minor importance, C. argyrosperma Huber ‘silver-seed gourd’ and C. ficifolia Bouché ‘fig-leaf cucurbit’.
Cucurbita value is based on the use of immature and mature fruit of summer and winter squashes, respectively (Ferriol and Picó, 2008). The Statistic Division of the Food and Agriculture Organization of the United Nations (FAOSTAT data, 2007) ranked world cucurbit production (including watermelons, cucumbers, squash, pumpkins, and gourds) among the 10 leading vegetable crops worldwide. Pumpkin, squash, and gourd production was ≈20 million tons with China as the major producer followed by India, Russia, and the United States.
Cucurbita moschata is a highly diverse winter squash species adapted to hot and humid weather and low altitudes. Fruit size and color are highly variable. Flesh colors range from light yellow to dark orange. Cucurbita moschata's largest genetic variability occurs in the American Tropics with variation increased by hybridization with wild species (Ferriol and Picó, 2008). The Butternut type of C. moschata is one of the most widely known in Europe and the United States.
Exotic germplasm and wild species from the USDA germplasm collection are used as genetic resources for breeding. Two wild squash species, C. lundelliana Bailey and C. okeechobeensis ssp. okeechobeensis Bailey, have been recently studied as useful sources for disease resistance such as powdery mildew and P. capsici crown rot resistance (Cohen et al., 2003; Contin and Munger, 1977; Metwally et al., 1996; Padley, 2008). Cucurbita lundelliana is native to the Yucatan peninsula and can be hybridized with C. moschata, C. maxima, C. ficifolia, C. pepo, and C. argyrosperma (Ferriol and Picó, 2008; Sitterly, 1972; Whitaker, 1959). Cucurbita okeechobeensis is formed by subspecies okeechobeensis and martinezii Walters & Decker. Subspecies martinezzi is endemic to Mexico, growing in the same region as C. moschata ssp. sororia Merrick & Bates (Ferriol and Picó, 2008). Cucurbita okeechobeensis ssp. okeechobeensis is endemic to Florida. This subspecies is currently categorized as rare or endangered in the National Germplasm Repository (GRIN, 2009), and it can be hybridized with C. ecuadorensis Cutler & Whitaker, C. moschata, C. argyrosperma, and C. pepo. Cucurbita lundelliana and C. okeechobeensis are also cross-compatible (Ferriol and Picó, 2008).
Interest in breeding for resistance to P. capsici is of importance because of the economic impact P. capsici syndromes can have on cucurbit production. This oomycete pathogen affects a wide range of solanaceous and cucurbitaceous plants worldwide (Erwin and Ribeiro, 1996; Tian and Babadoost, 2004). Infection can occur at any plant stage, producing damping-off, root rot, crown rot, foliar blight, and fruit rot symptoms (Hausbeck and Lamour, 2004). Losses resulting from P. capsici in commercial production can reach 100%. Chemical, cultural, and mechanical practices have been reported to reduce P. capsici infection, but multiple cycles of infection and spore production have made its control difficult (Babadoost et al., 2008; Hausbeck and Lamour, 2004). Furthermore, resistance to the fungicides mefenoxam and metalaxyl has been reported in P. capsici (Parra and Ristaino, 2001; Ristaino and Johnston, 1999). Genetic resistance to P. capsici would constitute an important component of P. capsici management.
Recently, resistance to the crown rot syndrome in squash has been introgressed into University of Florida breeding lines, Fla. 27-12 and Fla. 27-17, from C. lundelliana and C. okeechobeensis ssp. okeechobeensis through a series of hybridizations and single plant selections (Padley et al., 2008). The genetic composition of each line is 62.5% C. moschata, 25% C. lundelliana, and 12.5% C. okeechobeensis. Preliminary data also indicated that each line was segregating for resistance to foliar blight (Kabelka, personal communication). Unfortunately, transfer of these sources of resistance into a C. moschata background has proven to be challenging as a result of unmarketable fruit quality and hybridization barriers between species. The purpose of this research was to identify sources of resistance to P. capsici within the USDA C. moschata germplasm collection. This study included the evaluation of the crown rot screen's consistency, identification of resistant individuals, and the response of S1 progeny from resistant selections to P. capsici.
Babadoost, M., Tian, D., Islam, S.Z. & Pavon, C. 2008 Challenges and options in managing Phytophthora blight (Phytophthora capsici) of cucurbits. Proc IXth Eucarpia 2008 399 406
Barksdale, T.H., Papavizas, G.C. & Johnston, S.A. 1984 Resistance to foliar blight and crown rot of pepper caused by Phytophthora capsici Plant Dis. 68 506 509
Cohen, R., Hanan, A. & Paris, H.S. 2003 Single-gene resistance to powdery mildew in zucchini squash (Cucurbita pepo) Euphytica 130 433 441
Contin, M. & Munger, H.M. 1977 Inheritance of powdery mildew resistance in interspecific crosses with Cucurbita martinezii HortScience 12 397 (abstract).
Donahoo, R.S., Kousik, C.S. & Thies, J.A. 2009 Response of US Cucumis melo Plant Introductions to Phytophthora capsici Phytopathology 99 S29 (abstract).
FAOSTAT data 2007 <http://faostat.fao.org/faostat/collections?subset=agriculture>.
Ferriol, M. & Picó, B. 2008 Pumpkin and winter squash 317 349 Handbook of plant breeding: Vegetables I Asteraceae, Brassicaceae, Chenopodicaceae, and Cucurbitaceae Springer New York, NY
GRIN 2009 <http://www.ars-grin.gov/cgi-bin/npgs/html/tax_acc.pl>.
Hausbeck, M.K. & Lamour, K.H. 2004 Phytophthora capsici on vegetable crops: Research progress and management challenges Plant Dis. 87 63 68
Hwang, J.S. & Hwang, B.K. 1993 Quantitative evaluation of resistance of Korean tomato cultivars to isolates of Phytophthora capsici from different geographic areas Plant Dis. 77 1256 1259
Kim, E.S. & Hwang, B.K. 1992 Virulence to Korean pepper cultivars of isolates of Phytophthora capsici from different geographic areas Plant Dis. 73 745 747
Kousik, C.S. & Thies, J.A. 2010 Response of U.S. bottle gourd (Lagenaria siceraria) Plant Introductions (PI) to crown rot caused by Phytophthora Capsici Phytopathology 100 S65 (abstract).
Lee, B.K., Kim, B.S., Chang, S.W. & Hwang, B.K. 2001 Aggressiveness to pumpkin cultivars of isolates of Phytophthora capsici from pumpkin and pepper Plant Dis. 85 497 500
Metwally, E.I., Haroun, S.A. & El-Fadly, G.A. 1996 Interspecific cross between Cucurbita pepo L. and Cucurbita martinezii through in vitro embryo culture Euphytica 90 1 7
Padley L.D. Jr 2008 Identification and characterization of resistance to Phytophthora capsici within squash (Cucurbita spp.) Ph.D. diss., University of Florida
Padley, L.D. Jr, Kabelka, E.A. & Roberts, P.D. 2009 Inheritance of resistance to crown rot caused by Phytophthora capsici in Cucurbita HortScience 44 211 213
Padley, L.D. Jr, Roberts, P.D., French, R. & Kabelka, E.A. 2008 Evaluation of Cucurbita pepo accessions for crown rot resistance to isolates of Phytophthora capsici HortScience 43 1996 1999
Parra, G. & Ristaino, J.B. 2001 Resistance to mefenoxam and metalaxyl among field isolates of Phytophthora capsici causing Phytophthora blight of bell pepper Plant Dis. 85 1069 1075
Reifschneider, F.J.B., Café-Filho, A.C. & Rego, A.M. 1986 Factors affecting expression of resistance in pepper (Capsicum annuum) to blight caused by Phytophthora capsici in screening trials Plant Pathol. 35 451 456
Ristaino, J.B. & Johnston, S.A. 1999 Ecologically based approaches to management of Phytophthora blight on bell pepper Plant Dis. 83 1080 1089
Sy, O., Bosland, P.W. & Steiner, R. 2005 Inheritance of Phytophthora stem blight resistance as compared to Phytophthora root rot and Phytophthora foliar blight in Capsicum annuum L J. Amer. Soc. Hort. Sci. 124 14 18
Walker, S.J. & Bosland, P.W. 1999 Inheritance of Phytophthora root rot and foliar blight resistance in pepper J. Amer. Soc. Hort. Sci. 124 14 18