The development and evaluation of CSILs is of great importance in molecular breeding, and such stocks have been employed successfully in rice, where many CSILs have been developed [32]. Once favorable alleles in QTL/genes have been identified on introgressed segments, the CSILs become candidates for selection in subsequent molecular breeding strategies [26]. In this present study, we found a broad-spectrum resistant CSIL, IL089, which carried three introgressed segments located on Chrs.A7, D7, and D11. The segment on Chr.D7 conferred tolerance to the three Vorinostat mw V. dahliae isolates used in

this study. The segment on Chr.D11 was associated with resistance to the V. dahliae V07DF2 and D8092 isolates. When the two segments were combined in IL089, it was resistant to all three V. dahliae isolates. Combining Sirolimus cost different resistance QTL could allow breeding broad-spectrum resistant cultivars. For example, we could pyramid the following resistance QTL: qRV991-A3-2 (resistant to V. dahliae

V991), qRV07DF2-D11-1 (resistant to V. dahliae V07DF2) and qRD8092-A5-1 (resistant to V. dahliae D8092). These three high-resistance QTL could be combined to breed a cotton cultivar that exhibits broad-spectrum resistance to Verticillium wilt, using a modified backcrossing pyramiding breeding scheme with MAS. Such MAS breeding experiments are being conducted presently in our laboratory. Two cultivated tetraploid cotton species, G. hirsutum (AD)1 and G. barbadense (AD)2, contain the A and D subgenomes. The effects of the two subgenomes on yield and fiber quality are important research objectives for the production of tetraploid cultivars. A meta-analysis revealed that cotton fiber QTL are enriched in the Dt subgenome [33], but a more recent study showed that the subgenomic

distribution of fiber qualities is equally divided between the chromosomes of the two subgenomes [34]. In the present study, the number of additive QTL detected in the At sub-genome was approximately equal to that found in the Dt sub-genome in the same CSIL population [18]. This is the first report to consider the effect of the two subgenomes on resistance to Verticillium wilt. In the present study, we tried to analyze the effect of the two Non-specific serine/threonine protein kinase subgenomes on host resistance to Verticillium wilt. Eighteen QTL associated with resistance/susceptibility to one of the V. dahliae isolates assessed were detected and, of these, 16 QTL were located in the At subgenome and seven in the Dt sub-genome. A chi-square test of QTL distribution on the At/Dt sub-genomes showed no significant difference in the distribution of the QTL between these subgenomes. Similar results were obtained for the other two V. dahliae isolates. These results suggest that the effects of the two subgenomes on the numbers of resistance and susceptibility QTL were insignificant. The total additive effect of resistance or susceptibility QTL on the At sub-genome was negative, but the total effect on the Dt subgenome was positive.