Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2003
Publication Date: 10/15/2003
Citation: Lopez-Sese, A.I., Staub, J.E., Gomez-Guillamon, M.L. 2003. Genetic analysis of spanish melon (cucumis melo l.) germplasm using a standardized molecular marker array and reference accessions. Theoretical and Applied Genetics. Interpretive Summary: Plant species differ genetically for visual (phenotype) and cellular (pertaining to the cell) traits. Fruit yield and fruit quality are examples of phenotypic traits. The analysis of DNA (contained in the cell) of organisms is now used to determine differences between plants. The biotechnological tool associated with the analysis of DNA is called molecular marker analysis. Molecular markers are segments of DNA used to identify differences in DNA between organisms. Melon varieties differ in their plant habit (stature as small or large) and their DNA. Although Spanish melons differ in phenotype from U.S. melon types, the extent of differences in their DNA is not known. In contrast to U.S. melon varieties that are uniform (hybrids), Spanish melons are not uniform and are referred to as landraces. There are many attributes in Spanish landraces that might be used to improve U.S. melon (e.g., pest and disease resistance, fruit quality, and long self life). However, in order for U.S. public and private plant breeders to utilize Spanish landraces in their plant improvement programs, the phenotype and DNA variation (differences) among these landraces must be characterized and compared to the U.S. melon types. Therefore, an experiment was designed and executed to determine the phenotype and DNA variation among Spanish melon landraces. The data indicate that U.S. and Spanish melon are very different in both phenotype and DNA. The data also provide the plant breeder with working strategies for the incorporation of genes from Spanish landraces into U.S. melon types. This will allow the plant breeder to work more efficiently and effectively, and thus shortened the time to develop improved melon varieties for U.S. consumption. Improved melon varieties will in turn make the U.S. grower more competitive while providing an unique product to the U.S. consumer.
Technical Abstract: Genetic relationships among 125 Spanish melon (Cucumis melo L.) accessions from the germplasm collection at the regional Experimental Station, La Mayora (CSIC) Málaga, Spain were assessed using a standard molecular marker array consisting of 34 random amplified polymorphic DNA (RAPD) markers bands (19 primers) and 72 reference accessions drawn from previous studies. The reference accession array consisted of a broad range [Japanese (19) Crete (17), African (15) and USA and Europe (US/EU, 21)] of horticultural groupings (C. melo subsp. melo: Group Cantalupensis, Group Conomon, Group Inodorus, Group Flexuosus, and Group Chito), and of melon cultivar-groups (e.g., Charentais, Shipper (U.S. Western and European), Ogen, and Galia, Honeydew and Casaba). Cluster analysis of variation at polymorphic loci revealed that Spanish melon (largely Group Inodorus, Casaba melon types) was genetically distinct from the reference accessions and other Group Inodorus melons of different origins. Most African accessions showed common genetic affinities, and grouped with the Group Chito and Group Conomon accessions examined. Those accession groupings were distinct from all other accessions belonging to Group Cantalupensis, Flexuosus, and Inodorus accessions originating from Crete, Japan, Europe, and the U.S. Genetic diversity (relative polymorphism level as a ratio of percentage of polymorphism: number of accessions) was highest in accessions of African origin (5.7) and lowest in accessions of Spanish origin (0.7). Likewise, polymorphism level in Group Conomon (19.9) and Group Chito (10.3) was higher than Group Inodorus accessions (0.6). Additional RAPD markers (49 primers, 141 bands) and 22 selected agronomic traits (quantitative and qualitative) were then used to assess the genetic diversity among Spanish accessions. Cluster analysis using only fruit characteristics grouped accessions into cultivar-groups. In contrast, cluster analysis using only RAPD-based genetic distance estimates (GD; Jaccard's coefficient) did not provide consistent accession groupings either by cultivar-group or geographic origin. The mean GD among all Spanish accessions was 0.31 ± 0.08. The highest level of polymorphism based on population size was detected among melons originating from the central region of Spain (7.0-8.8), and in the Rochet cultivar-group (7.6). In contrast, melon accessions from the Andalucía region (1.6) and Green melon cultivar-groups (1.9) were comparatively less diverse. Cultivar-group heterogeneity was estimated by RAPD-based examination of accessions grouped by morphological analysis. The relatively high level of heterogeneity observed within cultivar-groups indicates that the Spanish melon accessions examined could be used to broaden the genetic base of local and foreign Casaba germplasm. Moreover, data indicate that the genetic diversity of U.S and European commercial melon germplasm (i.e., Groups Cantalupensis and Inodorus) could be enhanced by the introgression of genes from Spanish accessions, and that it would be advantageous to acquire additional Spanish landraces to ensure the retention and diversification of existing genetic diversity of the CSIC and other regional collections.