Association analysis in a germplasm panel of watermelon (Citrullus lanatus (Thunb.) Matsum and Nakai) predominantly from India confirms a QTL conferring resistance to Fusarium oxysporum f. sp. niveum race 1

An experiment was conducted to screen a germplasm panel comprising 331 Citrullus sp. accessions against Fon race 1 for identification of resistance and to validate a candidate QTL (Fon-1) region conferring resistance. The accessions were screened through artificial inoculation of spore suspension during the rainy season of 2017. A genotype with >= 67% survival at 28 days post-inoculation (DPI) was categorised as resistant. A total of 41 accessions were identified to possess resistance to Fon race 1. Of these, nine accessions were highly resistant (mean survival >= 90% at 28 DPI). The reactions of these accessions were also confirmed in another bioassay. These accessions need deployment in future watermelon breeding programmes. Six markers, located within the previously reported Fon-1 locus, were tested for their association with resistance and among them, InDel-4, located in the 5MODIFIER LETTER PRIME promoter region of an ABC Transporter protein, was found to be most significantly associated and explained maximum phenotypic variation, proving its relevance for marker-assisted introgression of resistance to Fon race 1 into elite commercial backgrounds of watermelon.