A Major QTL Is Associated with Fusarium Wilt Race 1 Resistance in Watermelon

Fusarium wilt is a major disease of watermelon caused by the soil-borne fungus Fusarium oxysporum Schlechtend.:Fr. f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hans (Fon). A genetic population of 186 F₃ families (24 plants in each family) exhibited continuous segregation for Fon race 1 response. Genotyping-by-sequencing (GBS) technology was used on these 91 selected F₂ samples to produce 266 single nucleotide polymorphism (SNP) markers, representing the 11 chromosomes of watermelon. A major QTL associated with resistance to Fon race 1 was identified with a peak logarithm of odds (LOD) of 33.31 and 1-LOD confidence interval from 2.3 - 8.4 cM on chromosome 1 of the watermelon genetic map.  This QTL is positioned in a genomic region where several disease-resistance candidate genes, known as pathogenesis-related (PR) protein gene sequences were identified.  Additional independent, but minor QTLs were identified on chromosome 1 (LOD 4.16), chromosome 3 (LOD 4.36), chromosome 4 (LOD 4.52), chromosome 9 (LOD 6.8), and chromosome 10 (LOD 5.03 and 4.26). The results in this study are useful for the identification of resistance genes and elucidating resistance to Fusarium wilt in watermelon.