A genetic map of melon highly enriched with fruit quality QTLs and EST markers, including sugar and carotenoid metabolism genes

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 in Israel and the US. The map includes 668 DNA markers (386 SSRs, 76 SNPs, six INDELs and 200 AFLPs), 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 1,222 cM with an average of 2.672 cM between markers. In addition, a skeleton physical map was initiated and 29 melon BACs harboring fruit ESTs were localized to the 12 linkage groups of the map. 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, as well as useful markers for breeding for fruit quality.

The PH gene determines fruit acidity and contributes to the evolution of sweet melons

“…1) that involved two individual intraspecific segregating populations: an RIL (recombinant inbred lines) population derived from a cross of the high-pH muskmelon (Reticulatus group) 'Dulce' and the low-pH Indian phut snapmelon (Momordica group) PI414723 (ref. 15), and a near-isogenic pair of melon lines segregating for the pH trait ( Fig. 2a-c), which were produced by crossing the high-pH cantaloupe (Cantalupensis group) 'Noy Yizre'el' and the low-pH snake melon (Flexuosus group) 'Faqqous' 16 .…”

“…Melon RILs (recombinant inbred lines). A recombinant inbred melon population was developed from a cross between 'PI414723'-S 5 (C. melo Momordica Group) and 'Dulce' (C. melo Reticulatus group) 15 . F 2 individuals (n ¼ 112) originating from two F 1 plants were propagated by single-seed descent to create the population, which consisted of 99 F 6 -, F 7 -and F 8 -generation RI lines.…”

“…This is in sharp contrast to the more primitive members of the species whose fruit are acidic when mature [12][13][14][15] . The genetic trait of sourness, or acidity, of melon fruit flesh is conferred by a single dominant locus termed So (Sour) or PH [14][15][16] . As all sweet melon accessions are non-acidic, they are homozygous for the recessive mutant, ph/ph.…”

Co-mapping studies of QTLs for fruit acidity and candidate genes of organic acid metabolism and proton transport in sweet melon (Cucumis melo L.)

“…reticulatus), an American muskmelon with non-sour, sweet fruit (Danin-Poleg et al 2002). F 2 individuals (n = 112) originating from two F 1 plants were propagated by the single-seed descent method to create the population, consisting of 99 RI lines comprising a mix of F 6 , F 7 and F 8 generations, as described in Harel-Beja et al (2010).…”

“…We present here a detailed QTL analysis of fruit pH and organic acid contents based on a recently described F 7 -F 8 RILs population (Harel-Beja et al 2010) derived from the PI 414723 £ 'Dulce' cross. Furthermore, we extend the signiWcance of this major QTL to additional C. melo genotypes and show that the same locus determines fruit acidity in a broad spectrum of melon groups.…”