Molecular markers assist in the development of diverse inbred backcross lines in European Long cucumber (Cucumis sativus L.)

Abstract

The popular fresh-market European Long cucumber (Cucumis sativus L.) is grown commercially worldwide under controlled, greenhouse environments. However, it has a narrow genetic base, where private and public improvement programs can trace their origins to comparatively few accessions. Therefore, a project was designed to identify diverse genotypes for use in the formation and analysis of inbred backcross (BC 2 S 3 ) lines (IBL) to broaden the genetic base of this market class. Initially, 42 cucumber accessions were evaluated with a previously defined standard marker array to identify parents for use in backcrossing. The IBL were developed by crossing the elite commercial line NZ1 (Nunhems Vegetable Seeds, Haelen, The Netherlands) and PI 432858 (China), and then backcrossing the most genetically diverse BC 1 and BC 2 progeny to the elite parent as defined by marker analyses (19 polymorphic, mapped SSR, and SCAR marker loci), followed by three generations of single seed descent resulting in 116 IBL (BC 2 S 3 ). The IBL were evaluated under greenhouse conditions for days to anthesis, sex expression, lateral branch number, yield, and exterior fruit quality in Madison, Wisconsin, USA (soil media), and in Haelen and Bergschenhoek, The Netherlands (soilless, hydroponic media). The IBL were genotyped using an expanded marker array (37 polymorphic SSR, SCAR, SNP, EST, BAC end, and gene-associated loci), and genetic relationships were examined by multivariate analyses using phenotypic and genotypic data. The 116 developed IBL possessed considerable morphological and genotypic diversity, where genetic distance (GD) among lines ranged between 0.00 and 0.77. These IBL possessed many commercially acceptable attributes, and, thus, genetic diversity in this market type could be substantially increased by the use of these genetically broad-based IBL during plant improvement.

USDA, ARS European Long Greenhouse Cucumber Inbred Backcross Line Population

“…The 116 IBL were developed by crossing the elite commercial line NZ1 (Nunhems Vegetable Seeds, Haelen, The Netherlands) and PI 432858 (Northern China, open-field and greenhouse type; donor parent) (Delannay, 2009;Delannay and Staub, 2010). The parents used for IBL development were selected during the marker analysis of 42 accessions [20 elite cucumber lines, 17 diverse PIs from the National Plant Germplasm System (NPGS) (Horejsi and Staub, 1999) and five breeding lines from the U.S. Department of Agriculture, Agricultural Research Service cucumber breeding project, Madison, WI (Delannay, 2009;Delannay and Staub, 2010).…”

“…The 116 IBL were developed by crossing the elite commercial line NZ1 (Nunhems Vegetable Seeds, Haelen, The Netherlands) and PI 432858 (Northern China, open-field and greenhouse type; donor parent) (Delannay, 2009;Delannay and Staub, 2010). The parents used for IBL development were selected during the marker analysis of 42 accessions [20 elite cucumber lines, 17 diverse PIs from the National Plant Germplasm System (NPGS) (Horejsi and Staub, 1999) and five breeding lines from the U.S. Department of Agriculture, Agricultural Research Service cucumber breeding project, Madison, WI (Delannay, 2009;Delannay and Staub, 2010). The standard cucumber marker array developed by Horejsi and Staub (1999) (44 mapped and 27 unmapped random amplified polymorphic DNA markers) was used to provide an initial estimate of GD (Jaccard, 1908) for use in a multivariate analysis to identity highly diverse parental lines using NTsys Version 2.01 computer software (Exeter Software, Setauket, NY).…”

“…A random F 1 from a cross between NZ1 and PI 432858 (donor parent) was crossed to a cloned (meristem-propagated) NZ1 plant (recurrent parent) to produce BC 1 progeny (Delannay, 2009;Delannay and Staub, 2010). At BC 1 , 30 of 288 individuals were selected (selection intensity = 11%) as possessing the highest heterozygosity based on molecular marker profiles [19 mapped, simple sequence repeat (SSR) and sequence characterized amplified region (SCAR) marker loci].…”

“…Approximately 13 plants from each of the 30 BC 2 families (384 plants) were marker-genotyped, and 120 BC 2 individuals were chosen (selection intensity = 31%) based on their heterozygosity at 44 markers (SSR, SCAR, single nucleotide polymorphism, expressed sequence tags, and bacterial artificial chromosome]. The selected BC 2 individuals were then self-pollinated for three generations by single seed descent to generate 116 BC 2 S 3 IBL (four of the 120 IBL did not produce sufficient seed amounts for phenotypic evaluation; Tanksley et al, 1996, Wehrhahn andAllard, 1965 (Delannay, 2009;Delannay and Staub, 2010). The morphological characteristics of a subset of 38 of the 116 (33%) IBL (randomly chosen) were then evaluated in Madison, WI, and in Haelen and Bergschenhoek, The Netherlands, under commercial greenhouse-growing conditions in 2008 (July to October) and 2009 (January to April) (Delannay, 2009;Delannay and Staub, 2010).…”

“…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.…”