Use of molecular markers to increase genetic diversity of Beit Alpha, European Long, and U.S. processing market classes of cucumber (Cucumis sativus L.) through marker-assisted selection

The genetic base of cucumber (Cucumis sativus L.) is extremely narrow with 3--8% molecular marker polymorphisms among elite (major market classes) and exotic cross-compatible germplasm, and 12% between botanical varieties. However, a broad genetic base is essential for the important market classes of cucumber (Beit Alpha, European Long, U.S. Processing) to meet biotic and abiotic threats to production. The primary germplasm collection, and secondary gene pool of cucumber are known to possess genetic diversity not present in commercial cucumber. Given the need to increase the genetic base of cucumber, a project was designed to develop and evaluate an array of genetically diverse inbred backcross lines (BC2S3; IBL) in Beit Alpha (Mediterranean), European Long, and U.S. processing market classes. In the Beit Alpha and European Long market classes, diverse accessions were genetically evaluated to identify the parental lines for IBL development. Based on their genetic distances, plants were identified in the Beit Alpha and European Long market classes for backcrossing. In the U.S. processing market class, parental lines for IBL formation were identified by a combining ability analysis. The IBL were formed in the three market classes by selecting the most genetically diverse BC1 and BC2 progeny followed by three generations of single seed descent to produce IBL. The IBL were then genotyped using molecular markers. Beit Alpha market class IBL were evaluated phenotypically in open-field and protected growing environments in the USA, The Netherlands, Israel, and Turkey. The European Long market class IBL were evaluated under hydroponic conditions in the USA and The Netherlands. The U.S. processing market class IBL were evaluated in two plantings in the open-field in the USA. Multivariate analyses using genotypic and phenotypic data indicated that IBL possessed considerable inter-line morphological and genotypic diversity that differed appreciably from parental lines. Given the genotypic and phenotypic diversity detected among IBL in each market class, these lines may prove useful in genetic studies and enhancing the genetic diversity of commercial cucumber.