Discovery of Fusarium Wilt Race 4 Resistance in Cotton

Fusarium wilt [Fusarium oxysporum f.sp. vasinfectum (FOV) Atk. Sny & Hans)] is a soil-inhabiting fungus that can survive for long periods in the absence of a host, making it impractical to eradicate from infested fields. This cotton host specific forms of the fungus is comprised of different genotypes called races. Over the past nine years, FOV race 4 has increasingly impacted cotton fields in California’s San Joaquin Valley (SJV) and represents an expanding threat to cotton production. Several parents and their derived populations were used in this study: three intraspecific (G. hirsutum x G. hirsutum L. and G. barbadense x G. barbadense L.) and five interspecific (G. hirsutum x G. barbadense) F₁, two intraspecific and four interspecific F2 populations. Inheritance and quantitative trait loci (QTL) mapping analyses identified a single resistance gene (Fov4) observed in F₂ populations based on inheritance of phenotypes. This single Fov4 gene had a major dominant gene action and conferred resistance to FOV race 4 in Pima-S6. The Fov4 gene appears to be located near a genome region on chromosome 14 marked with a QTL Fov4₁-C14. Detected QTL and identified SSR markers will be used to validate FOV resistance on additional mapping populations and FOV race resistance-comparisons. In addition, SSR markers will facilitate marker-assisted selection for the introgression of the Fov4 gene into improved upland germplasm for public release.