Submitted to: Journal of Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2000
Publication Date: N/A
Citation: Interpretive Summary: Commercial cultivars of melon are being continuously released by seed companies as they endeavor to improve its yield and quality. Because seed companies use only elite germplasm (lines and cultivar having been refined for economically important traits) their genetic diversity (their degree of similarity) is likely to be narrow. Narrow genetic diversity in crop species is not prudent since it results in a reduction in the type and number of genes required to combat the ever encroaching number of pests and pathogens which can reduce yield and quality. Thus, it is important to know the level of genetic diversity in a crop in order to determine how vulnerable it is to pathogens (organisms which attack plants). This study uses biotechnological tools (molecular markers) to assess the level of genetic diversity in the market classes of melons (e.g., cantaloupes, honeydews, casabas) in order to determine their genetic relatedness. It was determined that market classes are genetically distinct and that there are some unique cultivars that provide opportunities for increasing the genetic diversity in melon. This research will be useful to commercial seed companies that want to identify unique germplasm that will allow them to diversify their product line. Moreover, the estimation of genetic relationships identified in this study will provide seed companies with basic genetic information important to the legal protection of their varieties (i.e., plant patents).
Technical Abstract: Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to characterize genetic relationships among 46 accessions in four C. melo L. subsp. melo Groups (Cantaloupensis, Inodorus, Conomon, and Flexuosus). Genetic distance (GD) estimates were made among and between accessions in four melon market classes [Galia, Ogen, Charentais, and Shipper (European and U.S. types)] of Cantaloupensis, one market class of Inodorus (Casaba and Honey Dew), one accession of Conomon, and one accession of Flexuosus by employing three GD estimators; simple matching coefficient, Jaccard's coefficient, and Nei's distance-D. Differences detected among 135 RAPD bands and 54 SSR bands (products of 17 SSR primers) were used to calculate GD. Variation observed with 21 RAPD primers and 7 SSR primers was important in the detection of genetic differences. The GD of the Conomon and Flexuosus accessions was significantly different (P greater than 0.001) from the mean GD of all the market classes examined. Market classes were distinct (P greater than 0.001), such that GDs between Galia and other accessions were the largest (mean GD 0.34 to 0.35), and GDs between Ogen and other accessions were the smallest (mean GD 0.29 to 0.30). Contrasts between the U.S. shipper cultivar Top Mark and accessions within any market class was relatively large. Empirical estimations of variances associated with each marker type in the accessions examined indicated that, per band, lower coefficients of variation can be attained in the estimation of GD when using RAPDs compared to SSRs. Nevertheless, the genetic relationships identified using these markers were generally similar.