Evidence of the Role of QTL Epistatic Interactions in the Increase of Melon Fruit Flesh Content during Domestication

Cultivated melon was domesticated from wild melons, which produce small fruits with non-edible fruit flesh. The increase in fruit flesh is one of the major domestication achievements in this species. In previous work, a quantitative trait locus (QTL) on chromosome 6 (paqt6.1) linked to fruit flesh content was detected in a cross between cultivated (“Piel de Sapo”, PS) and wild (Ames 24294, TRI) accessions. The QTL was introgressed into the PS background, generating the TRI_6-3 introgression line (IL) that confirmed the effects of paqt6.1. The primary objective of this work was to fine-map paqt6.1 as the first step for the map-based cloning. Two different approaches were carried out; however, the results were not consistent, precluding the fine mapping of paqt6.1. TRI_6-3 and other related ILs were genotyped by genotyping-by-sequencing, finding additional introgressions in other chromosomes. In an F2 population from TRI_6-3-x-PS, we found an epistatic interaction between paqt6.1 and another locus on chromosome 11. The interaction was verified in advanced populations, suggesting that the effects of paqt6.1 are conditioned by the allelic composition at another locus in chromosome 11. Both loci should have TRI alleles to reduce the flesh content in the PS background. The implications on the history of melon domestication are discussed.