Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/1998
Publication Date: N/A
Interpretive Summary: Leaf rust and greenbugs are two major pests that reduce wheat yields every year. These two pests have the genetic ability to change and adapt to new wheat cultivars, resulting in new races or biotypes that can be more damaging than current populations of the pest. Fortunately, new sources of resistance genes are available in the form of other grass species that are relatives of wheat. Close relative like Triticum speltoides contain known resistance genes that can be transferred to cultivated wheat. In this study, one leaf rust and one greenbug resistance gene were transferred using a special procedure that resulted in pieces of Triticum speltoides chromosomes being fused with cultivated wheat chromosomes. Analysis of the plants recovered from this procedure revealed that the segment of Triticum speltoides chromosome where the leaf rust gene is located was transferred to the short arm of chromosome 7A of wheat. Likewise, the greenbug resistance gene from Triticum speltoides was transferred to the long arm o chromosome 7A. Molecular markers were identified for both resistance genes that can be used in a breeding program to quickly and efficiently develop new cultivars of wheat with resistance to leaf rust and greenbugs.
Technical Abstract: One leaf rust and one greenbug (Schizaphis graminum Rondani) resistance gene from chromosome 7S of Triticum speltoides were transferred to hexaploid wheat (Triticum aestivum L.) using the ph1b mutation that promotes homoeologous recombination. Primary recombinant chromosomes with crossovers proximal and distal to the resistance genes were identified and allowed to recombine to produce wheat chromosomes 7A with interstitial segments of T. speltoides chromatin. The leaf rust resistance gene, temporarily designated LrS7, was located on an interstitial chromosome segment from T. speltoides translocated to wheat chromosome arm 7AS. While physically located in the distal one third of the arm, genetically this segment was located 2 to 9 cM from the centromere and was 20 to 30 cM long. The greenbug resistance gene Gb5 was located on an interstitial T. speltoides chromosome segment translocated to wheat chromosome arm 7AL. This segment was located 18 to 22 cM from the centromere and was 40 to 50 cM long. RFLP markers Xabc465 (7AS) and Xpsr129 (7AL) were associated with the presence of LrS7 and Gb5 genes, respectively. Since the segments of T. speltoides chromosome 7S do not recombine with wheat chromosome 7A in the presence of the wild-type Ph1 locus, only one molecular marker per chromosome segment is required to monitor the introgressed genes in a marker-assisted selection program.