QTL-seq identifies and QTL mapping refines genomic regions conferring resistance to Fusarium oxysporum f. sp. niveum race 2 in cultivated watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]

The present experiment was conducted to map resistance to Fusarium oxysporum f. sp. niveum (Fon) race 2 in a highly resistant Citrullus lanatus accession (EC794421). For this purpose, a F2:3 population was developed by crossing a susceptible accession BIL-53 with EC794421. The F2:3 progenies were screened in two bioassays employing artificial inoculation of conidial suspension (1 x 106 conidia per ml; 5 ml per plant). Based on the F2:3 progeny performance, the five most resistant and sensitive F2 genotypes were identified and their corresponding genomic DNA was bulked to constitute the resistant and the susceptible bulks, respectively for performing QTL-seq analysis. Two statistically significant genomic regions were identified on chromosome 1 and chromosome 7; of which, the latter is novel and not reported earlier. Through target-locus refining employing QTL mapping, the QTLs on chromosomes 1 and 7 were narrowed down to two and a single microsatellite marker, respectively. These markers were also validated in two populations derived from different resistant accessions. The infor-mation generated in the current study will be of use of global breeders to incorporate the Fon race 2 resistance through marker-assisted introgression into elite commercial backgrounds of watermelon without incurring linkage drag.