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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 5ʹ 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. [ABSTRACT FROM AUTHOR]

• Loci conferring resistance to Fon race 2 was mapped following QTL-seq technique. • The mapped loci were refined through subsequent QTL mapping. • Markers identified would help in marker-assisted introgression of the target loci. 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 F 2:3 population was developed by crossing a susceptible accession BIL-53 with EC794421. The F 2:3 progenies were screened in two bioassays employing artificial inoculation of conidial suspension (1 × 106 conidia per ml; 5 ml per plant). Based on the F 2:3 progeny performance, the five most resistant and sensitive F 2 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 information 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. [ABSTRACT FROM AUTHOR]