QTL Mapping Identifies Novel Source of Resistance to Fusarium Wilt Race 1 in<i>Citrullus amarus</i>

Abstract

Fusarium wilt race 1, caused by the soilborne fungus <i>Fusarium oxysporum</i> Schlechtend.: Fr. f. sp. <i>niveum</i> (E.F. Sm.) W.C. Snyder & H.N. Hans (<i>Fon</i>), is a major disease of watermelon (<i>Citrullus lanatus</i>) in the United States and throughout the world. Although Fusarium wilt race 1 resistance has been incorporated into several watermelon cultivars, identification of additional genetic sources of resistance is crucial if a durable and sustainable level of resistance is to be continued over the years. We conducted a genetic mapping study to identify quantitative trait loci (QTLs) associated with resistance to <i>Fon</i> race 1 in segregating populations (F_2:3 and recombinant inbred lines) of <i>Citrullus amarus</i> (citron melon) derived from the <i>Fon</i> race 1 resistant and susceptible parents USVL246-FR2 and USVL114, respectively. A major QTL (<i>qFon1-9</i>) associated with resistance to <i>Fon</i> race 1 was identified on chromosome 9 of USVL246-FR2. This discovery provides a novel genetic source of resistance to Fusarium wilt race 1 in watermelon and, thus, an additional host-resistance option for watermelon breeders to further the effort to mitigate this serious phytopathogen.