The complex resistance to cucumber mosaic cucumovirus (CMV) in the melon accession PI161375 is governed by one gene and at least two quantitative trait loci

The complex resistance to cucumber mosaic virus (CMV) present in the exotic melon accession Sonwang Charmi PI161375 (SC) has been studied using two populations, a near-isogenic line (NIL) collection and a doubled haploid line (DHL) collection, both generated from a cross between SC and the cultivar Piel de Sapo as resistant and susceptible parents, respectively. The NIL collection had previously allowed us to describe a single recessive gene, cmv1, which conferred full resistance to CMV strains P9 and P104.82. Screening of the whole DHL population followed by quantitative trait locus (QTL) analysis revealed that resistance to the strains M6 and TL, both non-responsive to cmv1, was quantitative and governed by at least three QTLs. One of them, cmvqw12.1, co-located with cmv1 in linkage group (LG) XII. The QTL analysis mapped another two QTLs in LGIII (cmvqw3.1) and LGX (cmvqw10.1) and showed interaction between cmvqw12.1 and cmvqw3.1. Progeny of crosses between resistant DHLs carrying the three main QTLs showed complete resistance to the strain M6, validating the accuracy of the QTL analysis. However, in our screening, there were resistant DHLs carrying only two QTLs, suggesting that there are other regions involved in resistance to M6 and required when one of the main QTLs is missing. Therefore, resistance to CMV in melon SC is qualitative for some strains and quantitative for the rest. For this late resistance, cmv1 is necessary and explains most of the phenotypic variance, but it is not sufficient, and needs the interaction with other loci.