Submitted to: Molecular Breeding
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2008
Publication Date: 4/30/2008
Citation: Paris, M.K., Zalapa, J.E., Mccreight, J.D., Staub, J.E. 2008. Genetic Dissection of Fruit Quality Components in Melon (Cucumis melo L.) using a RIL Population Derived from Exotic x Elite US Western Shipping Germplasm. Molecular Breeding 22:405-419. Interpretive Summary: Melon is an economically important vegetable species of the taxonomic family Cucrbitaceae that possesses substantial morphological variation. This variation determines horticultural market class designations that include differences in mature fruit vary in shape, sweetness, color, soluble solids content, interior characteristics, diameter, and weight. It is important for genetic improvement efforts of plant breeders to know the kind and type of genetic factors (genes which control the inheritance of traits which are themselves located on chromosomes). The genetic factors controlling melon fruit quality are poorly understood. It would be important to locate the genes that control melon fruit quality on chromosomes so that breeding efficiency and effectiveness could be improved. Thus a study was undertaken to locate the genes for shape, sweetness, color, soluble solids content, interior characteristics, and diameter. Using a novel set of plants (lines) created by the joint USDA in Salinas CA and Madison WI the genes controlling these traits were defined and their potential for plant improvement evaluated. It was determined that plant breeders could use the information gathered on the location of the genes controlling these characters to improve their breeding efficiency and effectiveness. This will lead to more rapid development of improved higher quality cultivars for use by U.S. growers which will increase their global competitiveness.
Technical Abstract: Growing environment dramatically influences melon (Cucumis melo L.; 2n = 2x =24) fruit development and quality. Consequently, the characterization of quantitative trait loci (QTL) controlling melon fruit quality for application in marker-assisted selection (MAS) requires an assessment of genotype by environmental interactions, trait correlations, and QTL efficacy. Therefore, fruit quality traits [soluble solids content (SSC), mesocarp pressure (MP), fruit diameter (mesocarp + exocarp; FD), seed cavity diameter (endocarp; SCD), seed cavity to fruit diameter ratio (C:D), fruit shape (FS), and percentage of exocarp netting (PN) at time of harvest] were examined in 81 recombinant inbred lines (RIL) at two growing locations (California and Wisconsin, USA) to identify the map position and consistency of QTL for MAS in a Group Cantalupensis U.S. Western Shipping market type background. RIL developed from a cross between U.S. Department of Agriculture line USDA-846-1 and ‘Top Mark’ were used to identify 57 QTL (SSC = 10, MP = 8, FD = 6, SCD = 9, C:D = 8, FS = 10, and PN = 6) distributed across 13 linkage groups (LG) that explained a significant portion of the associated phenotypic variation (R2 = 4 to 29%). Broad-sense heritabilities obtained from RIL grown in California and Wisconsin were 0.47 and 0.56 for SSC, 0.65 and 0.75 for MP, 0.79 and 0.82 for FD, 0.78 and 0.69 for SCD, and 0.19 and 0.12 for C:D, respectively. The QTL map positions of SSC and FS were collinear with previous studies, and 13 location independent QTL [SSC (ssc4.5 and ssc5.6), MP (mp4.2, mp5.3, and mp7.5), SCD (scd1.1, scd3.3, scd8.4, and scd10.5), C:D (cd8.6), FS (fs3.2 and fs8.5), and one for PN (pn8.3)] were identified. The colinearity of these QTL with those identified on Group Inodorus-based maps, the positive phenotypic associations among these quality traits, and their consistency across diverse growing environments portends their broad applicability in melon MAS.