Mapping of genetic loci that regulate quantity of beta-carotene in fruit of US Western Shipping melon (Cucumis melo L.)

Melon (Cucumis melo L.) is highly nutritious vegetable species and an important source of beta-carotene (Vitamin A), which is an important nutrient in the human diet. A previously developed set of 81 recombinant inbred lines (RIL) derived from Group Cantalupensis US Western Shipper market type germplasm was examined in two locations [Wisconsin (WI) and California (CA), USA] over 2 years to identify quantitative trait loci (QTL) associated with quantity of beta-carotene (Q beta C) in mature fruit. A moderately saturated 256-point RIL-based map [104 SSR, 7 CAPS, 4 SNP in putative carotenoid candidate genes, 140 dominant markers and one morphological trait (a) spanning 12 linkage groups (LG)] was used for Q beta C-QTL analysis. Eight QTL were detected in this evaluation that were distributed across four LG that explained a significant portion of the associated phenotypic variation for Q beta C (R-2 = 8 to 31.0%). Broad sense heritabilities for Q beta C obtained from RIL grown in WI. and CA were 0.56 and 0.68, respectively, and 0.62 over combined locations. The consistence of Q beta C in high/low RIL within location across years was confirmed in experiments conducted over 2 years. QTL map positions were not uniformly associated with putative carotenoid genes, although one QTL (beta-car6.1) interval was located 10 cM from a beta-carotene hydroxylase gene. These results suggest that accumulation of beta-carotene in melon is under complex genetic control. This study provides the initial step for defining the genetic control of Q beta C in melon leading to the development of varieties with enhanced beta-carotene content.