Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2010
Publication Date: 4/17/2010
Citation: Harel-Beja, R., Portnoy, V., Fei, Z., Giovannoni, J.J., Ori, N., Lewinsohn, E., Tadmor, Y., Schaffer, A., Katzir, N. 2010. A genetic map of melon highly enriched with fruit quality QTLs and EST markers, including sugar and carotenoid metabolism genes. Theoretical and Applied Genetics. 121:511-533. Interpretive Summary: Cucumis melo L. (melon) is a highly diversified species that is widely cultivated throughout the world. Melon fruits are highly variable in shape, size, rind form, firmness, color and flavor. Fruits of wild and cultivated genotypes accumulate various levels of soluble sugars, organic acids, pigments and aroma volatiles, affecting fruit quality through complex networks of metabolic pathways that are active during fruit ripening. We describe an enriched melon map based on a unique, publicly available, recombinant inbred (RI) population developed from a cross between representatives of the two subspecies of melon: PI 414723 and 'Dulce’. These genotypes differ in numerous fruit quality traits, including flesh characters such as sweetness, acidity and color, external rind characters, size, shape and firmness. This RI population is therefore an excellent tool for the mapping of fruit quality traits. Over 30 genes encoding for the pathway of sugar metabolism were mapped, together with quantitative trait loci (QTL) for total soluble solids (TSS), sucrose and glucose accumulation. The RI population enabled the identification of six QTLs for sugar content, each of which contributes to sucrose levels in an additive manner. Genes of the carotenoid pathway and QTLs of fruit color were also mapped.
Technical Abstract: A genetic map of melon enriched for fruit traits was constructed, using a recombinant inbred (RI) population developed from a cross between representatives of the two subspecies of Cucumis melo L.: PI 414723 (subspecies agrestis) and 'Dulce' (subspecies melo). Phenotyping of 99 RI lines was conducted over three seasons in two locations. The map includes 668 DNA markers, of which 160 were newly developed from fruit ESTs. These ESTs include candidate genes encoding for enzymes of sugar and carotenoid metabolic pathways that were cloned from melon cDNA or identified through mining of the International Cucurbit Genomics Initiative database (http://www.icugi.org/). The map covers 1222 centimorgans with an average of 2.672 centimorgans between markers. Altogether, 44 fruit QTLs were identified: 25 confirming QTLs described using other populations and 19 newly described QTLs. The map includes QTLs for fruit sugar content, particularly sucrose, the major sugar affecting sweetness in melon fruit. Six QTLs interacting in an additive manner account for nearly all the difference in sugar content between the two genotypes. Three QTLs for fruit flesh color and carotenoid content were identified. Interestingly, no clear colocalization of QTLs for either sugar or carotenoid content was observed with over 40 genes encoding for enzymes involved in their metabolism. The RI population described here provides a useful resource for further genomics and metabolomics studies in melon.