USDA, ARS Beit Alpha Cucumber Inbred Backcross Line Population

Abstract

Beit Alpha cucumber (Cucumis sativus L.) is a Mediterranean fresh-market or processed type that originated in Israel for use in openfield and protected production (Shaw et al., 2000; Villalta et al., 2003). This market type develops moderately small (15 to 18 cm in length), slightly curved, uniform green, fruit with fine, and white spines without ridges, which is economically important in many Mediterranean production areas and has potential for protected production in the United States (Hochmuth et al., 2004; Shaw et al., 2007; Villalta et al., 2003). The cultivation of Beit Alpha cucumber is relatively recent, and this market type originated as a selection from a local landrace. Selection was reportedly initiated around 1950 on the Beit Alpha (synonym Beit Alfa or Bet Alfa) Kibbutz (a collective agrarian community) found in northern Israel near the Gilboa ridge (Davidi, 2009; Shaw et al., 2004). The initial breeding on this market type eventually produced a monoecious uniform variety for open-field production (Davidi, 2009). Public research on this market class in the United States has focused on best management practices to maximize its production (Shaw et al., 2000, 2004, 2007) and Israeli breeding efforts [public and private (Hazera Seeds)] that have yielded such varieties as ‘Delilah’ (Davidi, 2009). Using Japanese, Indian, Chinese, Dutch, and American germplasm, more modern commercial varieties possess resistances to viruses and downy mildew. Based on DNA polymorphisms, the genetic base of cucumber is extremely narrow {3% to 8% 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). The genetic base of several cucumber market types has been estimated using various molecular markers, and the genetic distance (GD) among Mediterranean-types (including the Beit Alpha type) is considered relatively broad (GD = 0.09–0.55) when compared with other cucumber market classes such as the European Long type (GD = 0.00– 0.24) (Dijkhuizen et al., 1996). Although genetic information regarding Beit Alpha types is limited (Hochmuth et al., 2004; Soleimani et al., 2009), Beit Alpha market type germplasm has potential as source material for U.S. breeding programs that develop cultivars for protected (gynoecious, mutiple pistillate, parthenocarpic) and open-field production (vegetative vigor, shortened days to anthesis, multiple lateral branching) environments (Sun et al., 2006). Dutch and Israeli seed companies have conducted intensive breeding of Beit Alpha cucumber. However, there are few public institutions directing efforts toward reporting the genetics and diversity of Beit Alpha germplasm, and none have provided highly inbred, genetically diverse germplasm for unfettered use in public breeding programs. Because of the lack of genetic information, insufficient publicly released germplasm, and its recent, single source origin (Israel), the genetic base of Beit Alpha cucumber germplasm should be diversified to maximize its use in plant improvement. 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 (Owens et al., 1985a, 1985b). This breeding method, when used in conjunction with marker-assisted selection (MAS) for maximum genetic diversity, can provide an array of homozygous lines that are heterogeneous with large percentages of the recurrent parent genotype ( 87%). Therefore, a series of Beit Alpha inbred backcross lines (BC2S3; IBL) were developed through MAS and phenotypic selection and released in January 2011 by the Agricultural Research Service, U.S. Department of Agriculture through its web-based documentation system (ARIS). Markers used in MAS were single sequence repeats (SSR), sequence characterized amplified regions (SCAR), and single nucleotide polymorphisms (SNP), in which their complete description is given in Delannay (2009) and Delannay and Staub (2010). This is the first public release of genetically diverse but highly inbred Beit Alpha germplasm. The IBL were made available to cucumber breeders to supply a source from which they may develop Beit Alpha market types with increased genetic diversity and yield potential suitable for open-field and greenhouse production. These IBL have use for the genetic analysis of complex traits (e.g., yield and quality components) that are common to most cucumber improvement programs (e.g., characterization of epistatic interactions; Robbins et al., 2008; Tanksley et al., 1996).