| Upland cotton (Gossypium hirsutum) is an economically important crop that provides natural fibers for the textile industry and seeds for oil, food and feed. Verticillium wilt (VW), caused by Verticillium dahliae Kleb., is a major constraint to cotton production in the United States and worldwide.;Tremendous efforts have been made to improve the resistance against VW. The objectives of this project were: (1) to evaluate the resistance of an interspecific backcross inbred line (BIL) population and an intraspecific recombinant inbred line (RIL) population; (2) to map quantitative trait loci (QTLs) conferring resistance to VW in the RIL and BIL population; and (3) to convert resistance gene analog- amplified fragment polymorphism (RGA-AFLP) markers into sequence tagged site (STS) markers that will facilitate marker-assisted selection (MAS) for VW resistance in cotton.;The BIL population, derived from a cross between a susceptible Upland cultivar, Sure-Grow (SG) 747 and a resistant Pima cultivar, Pima S-7 ( G. barbadense), was genotyped for VW resistance in both the greenhouse and field using a randomized complete block design (RCBD). Molecular markers from simple sequence repeat (SSR), AFLP, RGA-AFLP, single nucleotide polymorphism (SNP), cDNA-AFLP, and promoter anchored amplified polymorphism (PAAP) were used to construct a linkage map. The results showed that Pima cotton was more resistant to VW in the naturally infected field. However, the trend was reversed when an artificial wounding inoculation method was used in the greenhouse test. Of 160 polymorphic RGA-AFLP markers generated from 13 informative primer pairs, 42 were significantly correlated with one or more VW traits at the 0.05 probability or a higher level and 41 RGA-AFLP markers were placed on a linkage map of 292 markers covering 1,226 cM of the cotton genome. Three QTLs for VW resistance were detected, each of which explained 12.0 to 18.6% of the phenotypic variation.;The RIL population, derived from an intraspecific cross between a resistant genotype NM24016 and a susceptible genotype TM-1, was phenotyped twice in the greenhouse using RCBD. Individual plant reactions to VW infection were determined for disease incidence and severity at the seedling stage in different time intervals after inoculated with a defoliating V. dahliae isolate. The results confirmed that NM24016 was more resistant to VW than TM-1 and transgressive segregation occurred in that some RILs were more resistant than NM24016 and others more susceptible than TM-1. This study represents the first report to map QTLs conferring resistance to VW using a RIL population within Upland cotton. Three QTLs for VW resistance were located on the same chromosome (c19) using both the BIL and the RIL populations in the greenhouse and field tests for the first time. The markers associated with the VW resistance QTLs will facilitate fine mapping and cloning of VW resistance genes and marker-assisted breeding for VW resistant cultivars.;A total of 54 RGA-AFLP markers, including 26 from the BIL population and 28 from the RIL population, were cloned and sequenced. Of the 86 unique sequences, 51 were homologous to genes in the Cotton Gene Index (CGI) and 65 were homologous to genes in the NCBI databases. Many of these unique sequences showed similarity to genes encoding resistance-related products in different plant species, suggesting that RGA-AFLP markers were targeted to resistance gene regions in the cotton genome. The results provide evidence that RGA-AFLP markers can be sued for targeted mapping and marker development of disease resistance in plants. (Abstract shortened by UMI.). |
