Identification of major quantitative trait loci for parthenocarpic ability in East Asian melon

Natural (genetic) parthenocarpy contributes to fruit yield and quality under unfavorable environmental conditions where there are no effective pollinators or fertile pollen grains. Several old melon cultivars and weedy melon in East Asia are known to have strong parthenocarpic ability, but there has been little progress in intentionally introducing this ability into current F1 hybrid cultivars. Here, we examined its inheritance and confirmed the selection accuracy of DNA markers linked to it. We conducted QTL analysis using three F2 populations derived from crosses between a non-parthenocarpic cultivar and three parthenocarpic accessions, and detected two major QTLs on chromosomes 2 (par2.1) and 3 (par3.1). The parthenocarpic parent allele at both QTLs enhanced parthenocarpic ability. Phenotypic segregation was well explained by par2.1 and par3.1 in two F2 populations derived from Japanese weedy melon and an old Korean cultivar and by par3.1 in one from an old Japanese cultivar. This difference suggests that the effects of par2.1 and par 3.1 depend on genetic background. Both QTL regions contain several phytohormone-related genes, so we randomly selected SNPs in auxin- and ethylene-related genes to confirm the accuracy of selection for parthenocarpic ability. These SNP markers proved sufficient, though not perfect, to select plants with strong parthenocarpic ability. These results provide new insights into the molecular mechanisms of parthenocarpic ability in melon and will contribute to the development of new cultivars with high parthenocarpic ability. Key messageSeveral oriental melons have strong parthenocarpic ability controlled by one or two loci. DNA markers linked to these loci can select individuals with this ability.