Location: Crop Germplasm ResearchTitle: Quantitative trait locus mapping for Verticillium wilt resistance in a backcross inbred line population of cotton (Gossypium hirsutum × Gossypium barbadense) based on RGA-AFLP analysis Author
Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2013
Publication Date: 6/23/2013
Citation: Fang, H., Zhou, H., Sanogo, S., Flynn, R., Percy, R.G., Hughs, S.E., Ulloa, M., Jones, D.C., Zhang, J. 2013. Quantitative trait locus mapping for Verticillium wilt resistance in a backcross inbred line population of cotton (Gossypium hirsutum x Gossypium barbadense) based on RGA-AFLP analysis. Euphytica. 194:79-91. Interpretive Summary: Verticillium wilt is one of the most economically important diseases of cotton in the United States. Fortunately, the disease can be controlled effectively by developing and growing wilt resistant cultivars. However, the process of screening and identifying wilt resistant lines is extremely time consuming, labor intensive, and prone to error. The objective of this work has been to identify genetic factors (quantitative trait loci or QTL) within cotton that confer wilt resistance and develop molecular markers for those factors so that resistance can be easily identified. This study has identified two QTLs for Verticillium wilt resistance in cotton and found several tightly linked markers. The use of markers will greatly facilitate the development of wilt resistant cultivars, eliminating much of the large greenhouse and field screening processes now occurring at large labor and material costs.
Technical Abstract: Verticillium wilt (VW), caused by Verticillium dahliae, is one of the most important diseases in cotton. Development and growing of VW resistant cultivars is the most effective and economic strategy in controlling the disease. However, little is currently known on the genetic basis of VW resistance in cotton. The objective of this study was to map quantitative trait loci (QTLs) conferring VW resistance using resistance gene analog (RGA)- targeted amplified fragment length polymorphism (RGA-AFLP) markers in an interspecific backcross inbred line (BIL) mapping population of 146 lines. The BILs were developed from a cross between two tetraploid species, a susceptible Upland cultivar, Sure-Grow (SG) 747 (Gossypium hirsutum), and a resistant Pima cultivar, Pima S-7 (G. barbadense), followed by two generations of backcrossing using SG 747 as the recurrent parent. VW resistance was evaluated in replicated tests based on disease incidence in the field and disease incidence and severity in the greenhouse. Of 160 polymorphic RGA-AFLP markers, 42 were significantly correlated with one or more VW traits at the 0.05 probability or higher. Forty-one RGA-AFLP markers were placed on a linkage map which covered 1,226 cM of the cotton genome and contained 251 other molecular markers including simple sequence repeats (SSR). Three QTLs for VW resistance were detected using the linkage map, each of which explained 12.0 to 18.6% of the phenotypic variation. The two QTLs for disease incidence and severity detected in the greenhouse inoculation tests using root wounding were located on chromosome c4 and closely linked to four RGA-AFLP markers and therefore considered as the same QTL for VW resistance. The other QTL detected in the field test was located on c19 and flanked by several resistance gene targeted RGA-AFLP markers. The QTL allele on c4 for VW resistance detected in the greenhouse was from the susceptible parent SG 747 when the VW resistant Pima parent was more VW susceptible due to the disarmament of the first line of defense mechanism by root wounding inoculation. The other desirable VW resistance QTL allele on c19 was from the resistant parent Pima S-7, consistent with the fact that Pima cotton was more resistant to VW when naturally infected in the field. Using replicated tests on a permanent mapping population, this study has identified two QTLs for VW resistance in cotton and several tightly linked RGA-AFLP markers, which should facilitate the development of more sequence specific markers and the transfer of VW resistance from Pima to Upland cotton through marker-assisted selection.