Transfer of FHB Resistance from Thinopyrum elongatum to Spring Wheat.

In an ongoing search for additional sources of FHB resistance it was found that Thinopyrum elongatum 2x was a good source. Jan Dvorak of UC Davis had already produced the entire series of chromosome addition and substitution lines in a Chinese Spring (C.S.) background. Chromosome 7E was found to carry the best resistance. (8.0% infected florets compared to C.S. at 57.5%). The 7E (7D) substitution line was crossed to the C.S. Ph1b mutant to induce recombination between the two chromosomes. Progeny of plants with increased levels of meiotic chromosome pairing, homozygous for Ph1b and showing high levels of FHB resistance were selected for further study. Initially BC1F2 progeny were screened with chromosome 7E-specific SSR markers and resistance to FHB. Chromosome 7E-specific markers were obtained from published sequences and 7E-specific expressed markers produced in the lab of T. Ouellet. The objective was to isolate recombinants with minimal segments of chromosome 7E and yet carrying FHB resistance. Marked differences were observed between families for content of 7E chromatin. The number of 7E-specific bands expressed was as high as 23 in some families but reduced to single bands in selected later generations. To date in excess of 500 recombinants have been screened. In later generations, BC1F3 and BC1F4, large blocks of 7E chromatin were no longer present, but resistance at about the 10 % level persisted. Selected progenies are now being analyzed with SSR markers from chromosome 7D to determine the size and location of the 7E introgressions.