USDA, ARS European Long Greenhouse Cucumber Inbred Backcross Line Population

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Cucumber (Cucumis sativus L.; 2n = 2x = 14) is produced worldwide and is consumed as a fresh (fresh or slicing types) or as a processed vegetable [processing or pickling types and as a cooked vegetable (e.g., China)] product in several market classes (Staub et al., 2008). The European Long market-type cucumber is grown for the fresh market in protected-culture environments (primarily glasshouse and plastic ‘‘hoop houses’’). Harvestable fruit are 32 to 40 cm in length, smooth, dark green, fine-spined, and seedless (parthenocarpic, non-pollinated fruit set). Plants are gynoecious and develop multiple lateral branches that are pruned continuously, where single stems of plants are trained on trellis systems. Cucumber has an extremely narrow genetic base with 3% to 8% polymorphisms among elite and exotic germplasm and 12% between botanical varieties [C. sativus var. sativus L. and var. hardwickii (R.) Alef.] (Dijkhuizen et al., 1996; Horejsi and Staub, 1999; Meglic and Staub, 1996). The European Long market class has the narrowest genetic diversity [genetic distance (GD) = 0.00 to 0.24] among the major commercial cucumber market classes (e.g., Mediterranean types; GD = 0.09 to 0.55; Dijkhuizen et al., 1996; Horejsi and Staub, 1999). This is in large part the result of the initial use of relatively few PIs in germplasm development and the extensive use of the germplasm ‘‘Corona’’ in modern (since 1950) breeding (Staub et al., 2008; Kees Hertogh and Gerhard Reuling, personal communication, 2002). To our knowledge the last intensive, long-term public breeding effort for this market type ended in the 1950s (Andeweg, 1956). European Long Greenhouse cucumber breeding and genetics have been hampered by not only its lack significant genetic diversity, but also by the lack of appropriate genetic stocks for rapid genetic mapping of economically important traits and the inability to carry on strategic assessments of epistatic interactions. The inbred backcross breeding method (Wehrhahn and Allard, 1965) has been useful for broadening the genetic base of cucumber and providing novel populations for genetic analysis of complex traits in cucumber (Owens et al., 1985a, 1985b). Given the narrow germplasm base and the lack of ongoing public breeding efforts, a series of 116 European Long Greenhouse market-type IBL were developed (according to Wehrhahn and Allard, 1965) and released in Jan. 2011 by the Agricultural Research Service, U.S. Department of Agriculture. The IBL were developed by initially crossing an elite commercial European Long Greenhouse line and PI 432858 (China; long-fruited, Northern Chinese protected-culture type) followed by markerassisted backcrossing and self-pollination (Delannay, 2009; Delannay and Staub, 2010). A broad array of genetically diverse IBL is now available to cucumber breeders for developing long-fruited greenhouse market types with increased genetic diversity and yield potential suitable for protected-culture production. These IBL have use for the genetic analysis of complex traits (e.g., yield and quality components; characterization of epistatic interactions) that are common to most cucumber improvement programs (Robbins et al., 2008; Tanksley et al., 1996) and/or to evaluate cross-progeny derived from IBL and elite long-fruited germplasm during cultivar development.