Genetic variation in cucumber (Cucumis sativus L.) as assessed by random amplified polymorphic DNA1

Isozyme and restriction fragment length polymorphisms (RFLPs) have been applied to studies of genetic relationships and germplasm management in cucumber (Cucumis sativus L.). However, isozymes identify relatively few polymorphisms, and RFLPs are technically complex, expensive, and not compatible for the high through-put required for rigorous assessment of this narrow-based germplasm. Since random amplified polymorphic DNA (RAPD) markers do not manifest such shortcomings, a study was conducted in cucumber to examine genetic relationships in diverse germplasm, assess the usefulness of RAPD markers in distinguishing elite accessions, and compare the relative effectiveness of RAPD markers to that of isozyme and RFLP markers. One hundred and eighteen C. sativus accessions were analyzed using variation at 71 RAPD loci (44 mapped and 27 unmapped). Genetic distances among accessions were estimated using the simple matching coefficient complement, and analyzed using multi-dimensional scaling. Each accession had a unique marker profile, indicating that RAPD analysis was useful in genotypic differentiation. Germplasm grouping patterns were consistent with individual accession origins, theoretical dispersal routes and discriminating morphological characters (i.e., sex expression and fruit length to diameter ratio). Although elite accessions were discriminated by RAPD profiling, their genetic distances were relatively small (between 0.01 and 0.58), indicating limited genetic diversity in this germplasm array. Assessment of a subset of the germplasm array using RAPDs resulted in genetic distance measurements more similar to published genetic distance estimates by RFLP markers (Spearman rank correlation, rs = 0.7–0.8) than estimates by isozyme markers (rs = 0.4). Data indicate that RAPD markers have utility for analysis of genetic diversity and germplasm management in cucumber.