ARS | Publication request: Molecular and cytogenetic characterization of a durum wheat Aegilops speltoides chromosome translocation conferring resistance to stem rust

Submitted to: Chromosome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2008
Publication Date: October 17, 2008
Citation: Faris, J.D., Xu, S.S., Xiwen, C., Friesen, T.L., Jin, Y. 2008. Molecular and cytogenetic characterization of a durum wheat Aegilops speltoides chromosome translocation conferring resistance to stem rust. Chromosome Research. 16(8): 1097-1105.

Interpretive Summary: Stem rust is a serious disease of wheat that has caused historical epidemics, but it has not been a threat in recent decades in North America due to the eradication of the alternate host and deployment of resistant cultivars. However, the recent emergence of the stem rust race Ug99 poses a threat to global wheat production because most currently grown wheat varieties are susceptible. The wild relatives of wheat, such as Ae. speltoides, are a rich source of genetic variation and can often contain novel disease resistance genes. In this work, we characterized the chromosome constitution of a durum wheat line that had a segment of an Ae. speltoides chromosome translocated to one of the native durum chromosomes. Evaluation of the durum – Ae. speltoides chromosome translocation line for reaction to stem rust indicated that it was resistant to numerous races of stem rust, including Ug99. The original durum line was susceptible to these races of stem rust indicating that the Ae. speltoides chromosome segment involved in the translocation harbored a novel stem rust resistance gene(s). Analysis of the translocated chromosome with molecular tools revealed that a large portion of Ae. speltoides chromosome 2S was translocated to a small segment of the long arm of durum chromosome 2B. Efforts are ongoing to reduce the size of the Ae. speltoides chromosome segment to eliminate potentially deleterious genes on the segment while retaining the stem rust resistance gene(s). Deployment of the stem rust resistance gene(s) in the durum – Ae. speltoides chromosome translocation line will provide a strong line of defense against the devastating effects of Ug99.

Technical Abstract: Stem rust is a serious disease of wheat that has caused historical epidemics, but it has not been a threat in recent decades in North America due to the eradication of the alternate host and deployment of resistant cultivars. However, the recent emergence of Ug99 (or race TTKS) poses a threat to global wheat production because most currently grown wheat varieties are susceptible. In this study, we evaluated a durum wheat – Aegilops speltoides chromosome translocation line (DAS15) for reaction to Ug99 and six other races of stem rust, and used molecular and cytogenetic tools to characterize the translocation. DAS15 was resistant to all seven races of stem rust. Two durum – Ae. speltoides translocated chromosomes were detected in DAS15. One translocation involved the short arm, centromere, and a major portion of the long arm of Ae. speltoides chromosome 2S and a small terminal segment from durum chromosome arm 2BL. Thus, this translocated chromosome is designated T2BL-2SL•2SS. Cytogenetic mapping assigned the resistance gene(s) in DAS15 to the Ae. speltoides segment in T2BL-2SL•2SS. The Ae. speltoides segment in the other translocated chromosome did not harbor stem rust resistance. A comparison of DAS15 and the wheat stocks carrying the Ae. speltoides-derived resistance genes Sr32 and Sr39 indicated that stem rust resistance gene present in DAS15 is likely novel and will be useful for developing germplasm with resistance to Ug99. Efforts to reduce Ae. speltoides chromatin in T2BL-2SL•2SS are currently in progress.