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

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 (BC2S3) 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 BC1 and BC2 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 (BC2S3). 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.