| Wheat head scab is a very destructive fungal disease. Based on the mapping data of 700 AFLP and SSR markers in a population of 133 recombinant inbred lines (RILs) derived from Ning7840/Clark, three chromosomal regions associated with scab resistance were detected in a common cultivar, Ning7840. Interval analysis based on the integrated map of AFLP and SSR markers showed that the major 3BS QTL was located in a chromosome region about eight cM in length around Xgwm533 and Xbarc147. Based on mapping of six SSR markers on eight 3BS deletion lines, the major QTL was located distal to the breakage point 3BS-8. Two SSR markers, Xgwm120 and Xgwm614, were significantly associated with QTL for scab resistance on chromosome 2BL and 2AS, respectively. The resistance alleles on 3BS, 2BL and 2AS were all derived from Ning7840. Significant interaction between the major QTL on 3BS and QTL on 2BL was detected based on SSR markers linked to them. Two resistant by susceptible populations, both using Ning7840 as the source of resistance, were developed to examine the effect of the 3BS QTL in different genetic backgrounds. Marker-assisted selection (MAS) for the QTL with the SSR markers combined with phenotypic selection was more effective than selection based solely on phenotypic evaluation in early generations. Near-isogenic lines for the 3BS QTL were isolated from the F6 generation of the cross Ning7840/IL89-7978. Two sets of Chinese Spring (Sumai3) substitution lines were verified with chromosome specific SSR markers that were polymorphic between Sumai3 and Chinese Spring. These substitution lines were used to evaluate Type II and Type V resistance. Significant differences in Type II scab resistance and DON levels among different Chinese Spring (Sumai 3) substitution lines were detected. Positive chromosome substitution effects on Type II scab resistance were found on chromosomes 2B, 3B, 6B, and 7A from Sumai 3. Chromosomes 3B and 7A also reduced DON accumulation within the kernels, while chromosomes 1B, 2D, and 4D from Sumai 3 increased DON concentration. Chromosome 7A from Sumai 3 had the largest effect on resistance to scab spread and DON accumulation. |
