Advanced Genetic Studies on Powdery Mildew Resistance in TGR-1551

Cucurbits powdery mildew (CPM) is one of the main limiting factors of melon cultivation worldwide. Resistance to races 1, 2, and 5 has been reported in the African accession TGR-1551, whose resistance is controlled by a dominant–recessive epistasis. The dominant and recessive quantitative trail loci (QTL) have previously been located in chromosomes 5 and 12, respectively. We used several densely genotyped BC(3) families derived from the cross between TGR-1551 and the susceptible cultivar ‘Bola de Oro’ to finely map these resistance regions. The further phenotyping and genotyping of the selected BC(5), BC(5)S(1), BC(5)S(2), BC(4)S(1), BC(4)xPS, and (BC(4)xPS) S(1) offspring allowed for the narrowing of the candidate intervals to a 250 and 381 kb region in chromosomes 5 and 12, respectively. Moreover, the temperature effect over the resistance provided by the dominant gene has been confirmed. High resolution melting markers (HRM) were tightly linked to both resistance regions and will be useful in marker-assisted selection programs. Candidate R genes with variants between parents that caused a potential modifier impact on the protein function were identified within both intervals. These candidate genes provide targets for future functional analyses to better understand the resistance to powdery mildew in melons.