Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/1999
Publication Date: N/A
Citation: Interpretive Summary: Genetic variability (differences in DNA constitution) is necessary for crop improvement. Substantial effort has been directed towards collecting, preserving, and evaluating the breath of genetic variability in cucumber. Biotechnological tools called molecular markers are used to quantify the amount of genetic variation in the DNA of cucumber. Through their use, scientists have categorized the relationships among cucumber plants (germplasm) in the U.S. National Germplasm collections (NPGC). An non-radioactive, inexpensive and simple marker type called "RAPD" has not been applied to the analysis of genetic diversity in cucumber. Therefore, a study was designed to assess the genetic diversity of 118 different cucumber from the NPGC using RAPD markers and comparing the results with other types of molecular markers. Data indicate that results from RAPD markers compare favorably to those from other markers. Thus, scientists can use RAPD marker technology effectively to replace hazardous and expensive markers in germplasm diversity assessment, seed purity analysis, and plant variety protection. The use of RAPD markers for these purposes will increase efficiency and decrease costs to the seed industry.
Technical Abstract: Random amplified polymorphic DNA (RAPD) markers were used to examine genetic relationships in diverse germplasm, assess the usefulness of RAPD markers in distinguishing elite cucumber (Cucumis sativus L.) accessions, and compare the relative effectiveness of RAPD markers to that of isozyme and RFLP markers. One hundred 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 multidimensional 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 to 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 to 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.