ARS | Publication request: FREQUENCY DIFFERENCES OF RAPD MARKERS IN MELON MARKET CLASSES (CUCUMIS MELO L.)

Submitted to: Cucurbit Genetics Cooperative Report
Publication Type: Research Notes
Publication Acceptance Date: December 15, 2001
Publication Date: N/A

Interpretive Summary: The diversity (i.e., differences among individuals) of crop species is decreasing as man breeds more uniform, genetically similar plant types for agricultural use. The U.S. government finances the preservation of wild and exotic individuals (germplasm) in germplasm collections. These germplasm collections are housed at U.S. Department of Agriculture (USDA) research centers. For example, melon germplasm that has been collected from worldwide sources is held at the USDA Plant Introduction Station at Ames, Iowa. Elite germplasm is the product of breeding in seed companies. This germplasm contrasts with germplasm available from USDA plant introduction centers in that it has a comparatively narrow genetic base. That is, the differences between individuals in elite germplasm collections are less than that found in USDA collections. Molecular tools, one being RAPD, can be used to estimate the differences between elite commercial market class melons (e.g., cantaloupe and honeydew melons) and diverse USDA germplasm collections. A study was designed to use RAPD as a tool to examine the genetic differences among and between elite and diverse germlasm. It was found that the differences between elite European and U.S. melon germplasm was not as great as that between these and diverse African germplasm. Nevertheless, differences among elite germlasm were relatively large. This indicates that plant breeders interested in increasing the diversity of their germplasm can do so by using germplasm contained in the USDA collection. Increasing genetic diversity will reduce the risk of melons to biotic (e.g., disease) and abotic (e.g., drought) stress, and thus increase productivity.

Technical Abstract: The determination of variability in Cucumis melo L. market classes is of importance to germplasm management, plant variety protection, and in the development of breeding strategies. The genetic diversity of several commercially important melon groups (principally Cantaloupensis and Inodorus) has been characterized using molecular analyses [i.e., simple sequence repeat (SSR) and random amplified polymorphic DNA (RAPD) markers] have been used to differentiate elite melon germplasm. This paper provides a summary of the RAPD variation of major market class accessions [Charentais (7), European (6), U.S. Western Shipper (3), U.S. Eastern Market (4), Galia (7), Ogen (6), Honeydew (2), Cassaba (9), group Conomon (1), and group Flexuosus (1) accessions] given in previous publications. The vast majority of RAPD markers were found to have a similar percent frequency in accessions in Europe and USA. All groups showed a similar average percent frequency across markers. Given the relatively large standard deviations from mean values, the variation in all the market classes examined was relatively large. The great majority of polymorphisms was observed in this study provide for adequate variation to elucidate within and among group differences. Germplasm analysis of economically important crop species is key to their effective and efficient use in plant breeding programs. The summary presented in this paper will allow researchers to development a RAPD marker array(s) to best suit their needs for strategic analyses of germplasm. As a result, germplasm curators and breeders will be able to partition germplasm collections for more effective introgression of diversity into elite lines.