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

Authors: DELANNAY, ISABELLE - University Of Wisconsin; Staub, Jack

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2011
Publication Date: 9/2/2011
Citation: Delannay, I.Y., Staub, J.E. 2011. Molecular markers assist in the development of diverse inbred backcross lines in European long cucumber (Cucumis sativus L.). Euphytica. 178:229-245.

Interpretive Summary: The European Long market type cucumber produces a long (16 to 20 inches in length), smooth, dark green, fine-spined, seedless fruit. Although the cultivation of this market type is historic, the last intensive, long-term public breeding effort ended in the 1950s. Since then, plant improvement of this market type has been conducted almost exclusively by private seed companies, primarily in The Netherlands. Current research on European Long cucumbers in public institutions focuses mainly on management practices to maximize productivity within protected growing environments (primarily glasshouse and plastic "hoop houses"). A majority of the commercial European Long cultivars are of Dutch origin, and are grown hydroponically in rock wool under highly controlled environmental conditions. Plants are female flowering and develop multiple lateral branches that are pruned continuously to form an aerial leaf mat attached to lattice structures. Hydroponic plant culture in protected environments allows for year-round production of high quality fruit. The U.S. market for this particular cucumber type has increased in recent years, particularly in the southern U.S. The genetic diversity of European cucumber market types has been well documented, and found to be extremely narrow (3-5% among cultivars). This lack of genetic diversity has been an impediment to the genetic improvement of cucumber. There is a need to increase the genetic diversity of European cucumber to allow cucumber breeders more opportunity to identify unique and novel types (i.e., that possess greater virus and cold temperature resistance). Therefore, a study was designed to increase the genetic diversity in this market type by complex matings with another commercial cucumber type followed by improvement using biotechnologies (i.e., marker-assisted selection = MAS). The resulting progeny were evaluted in field trials to determine their potential for use in modern plant breeding programs. The results indicated that the resulting progeny were very diverse genetically (as defined by MAS) and had yield and quality characteritics that would allow their successful inclusion into private and public plant breeding programs for cucumber improvement. The resulting progeny will provide a new source of plant material currently not available in commercial cucumber to improve the yield and quality of this crop species. The resulting products (cultivars) will make the U.S. grower more competitive in the global market place and provide managerial flexibility that does not now exist in production of this crop.

Technical 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 (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.