QTLs mapping for Verticillium wilt resistance at seedling and maturity stages in Gossypium barbadense L

Verticillium wilt (Verticillium dahliae) is a major concern for cotton producers and consumers. The major strategy to control disease has been the development of resistant varieties of Gossypium. To identify Verticilium resistant genes in cotton, we generated F₂ and BC₁ populations by crossing a tolerant cultivar of Gossypium barbadense var. Hai 7124 with a susceptible cultivar, Gossypium hirsutum var. Junmian 1. Individual plant reaction to disease was quantified using a leaf trait in the seedling stage and a vascular tissue trait in mature stage. Two genetic linkage maps were constructed with SSR, RGA and DDRT markers. Four QTLs for the leaf trait, located on chr. A5, A7 and A8 and three QTLs for the vascular tissue trait on chr. A5, A7 and A9 were detected by composite interval mapping (CIM) in F₂ inoculated with a non-defoliating isolate BP2. BC₁S₂ families were planted separately and inoculated with the isolates, BP2, VD8 and 592. In the BP2 nursery, one QTL located on chr. D4 for the leaf trait and two QTLs on chr. D4 and A8 for the vascular tissue trait were detected. We detected two QTLs on chr. A5 and A8 for the leaf trait and three QTLs on chr. A5, D5 and D11 for the vascular tissue trait in plants grown in the VD8 nursery. In the 592 nursery, three QTLs on chr. A5 and D5 for the leaf trait and two QTLs on chr. D5 and D11 for the vascular tissue trait were detected. The present QTL mapping results revealed that two stable QTLs existed in different populations, four QTLs expressed at both the seedling and mature stages, and some QTLs controlling resistance to Verticillium wilt were located on different chromosomes and in different developmental stages for different isolates. The markers associated with these QTLs may facilitate the use of Verticillium wilt resistant genes in resistant breeding programs for cotton.