Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2013
Publication Date: 5/5/2013
Citation: Ulloa, M., Hutmacher, R.B., Roberts, P.A., Wright, S.D., Nichols, R.L., Davis, R.M. 2013. Inheritance and QTL mapping of Fusarium wilt race 4 resistance in cotton. Journal of Theoretical and Applied Genetics. 126:1405-1418. Interpretive Summary: Over the past nine years, Fusarium wilt disease has increasingly impacted cotton fields in California’s San Joaquin Valley. This disease is caused by a soil-inhabiting fungus that reduces yield in cotton. Planting resistant cotton varieties is the most economical method to reduce yield losses. Studies on progeny derived from crosses of Upland and Pima cottons identified a major resistance gene for race 4 of the Fusarium (Fov4) fungus. This single Fov4 gene had a major dominant expression and conferred resistance to FOV race 4 in Pima-S6. This dominant resistance gene (Fov4) was found to play a significant role in conferring resistance in different cotton genetic backgrounds. We suggest that this gene should be a primary target for breeding Fusarium-resistant cotton. In addition, molecular markers (small pieces of DNA that can be detected chemically) were identified to be associated with Fusarium wilt race 4 resistance. Analyses indicated the involvement in Fusarium resistance of additional marker-genes on six cotton chromosomes. Molecular markers are powerful tools for identifying Fusarium-resistant cottons, with the goal of reducing dependence on laborious field and greenhouse evaluations. Identified molecular markers should be useful for breeding Fusarium wilt resistance into elite cotton cultivars by marker-assisted selection.
Technical Abstract: Diseases such as Fusarium wilt [Fusarium oxysporum f.sp. vasinfectum (FOV) Atk. Sny & Hans)] represent expanding threats to cotton production. Integrating disease resistance into high-yielding, high-fiber quality cotton (Gossypium spp.) cultivars is one of the most important objectives in cotton breeding programs worldwide. In this study, we conducted a comprehensive analysis of gene action in cotton governing FOV race 4 resistance by combining conventional inheritance and quantitative trait loci (QTL) mapping with molecular markers. A set of diverse cotton populations was generated from crosses encompassing multiple genetic backgrounds. FOV race 4 resistance was investigated using seven parents and their derived populations: 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, and one RIL populations. Parents and populations were evaluated for disease severity index (DSI) of leaves, and vascular stem and root staining (VRS) in four greenhouse and two field experiments. Initially, a single resistance gene (Fov4) model was 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 Fov4-C14, which made the biggest contribution to the FOV race 4 resistance of the generated F2 progeny. Additional genetic and QTL analyses identified a set of 11 SSR markers that indicated the involvement of multiple genes and interactions across six linkage groups/chromosomes (3, 6, 8, 14, 17, and 25) in the inheritance of FOV race 4 resistance. QTLs detected with minor effects in these populations explained 5 – 19 percent of the DSI or VRS variation. The identified SSR markers will facilitate marker assisted selection for the introgression of individual genes or combination of genes for FOV resistance into elite cultivars. In addition, the QTLs with minor effects represent an additional resource for crop improvement and protection.