Quantitative Trait Loci Mapping of Multiple Independent Loci for Resistance to Fusarium oxysporum f. sp vasinfectum Races 1 and 4 in an Interspecific Cotton Population

Fusarium wilt, caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. vasinfectum, is a vascular disease of cotton (Gossypium spp.). E oxysporum f. sp. vasinfectum race 1 (FOV1) causes major plant injury and yield loss in G. hirsutum cultivars with coinfection with root-knot nematode (Meloidogyne incognita), while E oxysporum f. sp. vasinfectum race 4 (FOV4) causes plant damage without nematode coinfection in G. hirsutum and in G. barbadense cultivars. Quantitative trait loci (QTL) analysis of the interspecific cross G. barbadense Pima S-7 x G. hirsutum Acala NemX revealed separate multiple loci determining resistance to FOV1 and FOV4, confirming that race specificity occurs in E oxysporum f. sp. vasinfectum. Based on the area under the disease progress stairs, six major QTLs on chromosomes (Chrs) 1, 2, 12, 15 (2), and 21 contributing 7 to 15% to FOV1 resistance and two major QTLs on Chrs 14 and 17 contributing 12 to 33% to FOV4 resistance were identified. Minor-effect QTLs contributing to resistance to both FOV1 and FOV4 were also identified. These results define and establish a pathosystem of race-specific resistance under polygenic control. This research also validates the importance of previously reported markers and chromosome regions and adds new information for the location of E oxysporum f. sp. vasinfectum resistance genes. Some F8 recombinant inbred lines have resistance to both FOV1 and FOV4 and also to root-knot nematode, providing multiple resistance sources for breeding.