Identification of a major dominant gene for race-nonspecific tan spot resistance in wild emmer wheat

Authors: Faris, Justin; Overlander-Chen, Megan; KARIYAWASAM, GAYAN - North Dakota State University; CARTER, ARRON - Washington State University; Xu, Steven; LIU, ZHAOHUI - North Dakota State University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2019
Publication Date: 12/19/2019
Citation: Faris, J.D., Overlander, M., Kariyawasam, G.K., Carter, A., Xu, S.S., Liu, Z. 2019. Identification of a major dominant gene for race-nonspecific tan spot resistance in wild emmer wheat. Theoretical and Applied Genetics. 133:829-841. https://doi.org/10.1007/s00122-019-03509-8.
DOI: https://doi.org/10.1007/s00122-019-03509-8

Interpretive Summary: Tan spot is a serious fungal disease of both common wheat, which is used primarily for bread, and durum wheat, which is used to make pasta. The disease affects the leaves of the plants causing large lesions that limit photosynthetic capacity of the plant and ultimately causes reductions in yield and quality. Genetic resistance to tan spot has been identified in common wheat, and it has been used to develop modern varieties with good tan spot resistance. However, less work has been done in durum wheat, and until now, no good levels of tan spot resistance have been identified. Wild emmer wheat is a close relative of durum wheat, and it often possesses disease resistance genes that can be transferred to durum by way of conventional hybridization. In this study, researchers analyzed a set of durum lines that carried individual chromosomes from wild emmer for reaction to tan spot. The line that carried the chromosome known as “3B” from wild emmer was highly resistant to tan spot indicating that it harbored a highly effective tan spot resistance gene that functioned in durum wheat. Additional genetic analyses revealed the location of the gene on the chromosome. Molecular markers tightly associated with the gene were developed, which can be used by researchers to efficiently move the tan spot resistance gene into modern durum wheat varieties using conventional crossing techniques. The results of this study will lead to the development of durum wheat varieties with improved performance that suffer less yield reduction due to the tan spot disease.

Technical Abstract: Tan spot is an important foliar disease of durum and common wheat caused by the necrotrophic fungal pathogen Pyrenophora tritici-repentis. Genetic studies in common wheat have shown that pathogen-produced necrotrophic effectors interact with host genes in an inverse gene-for-gene manner to cause disease, but quantitative trait loci (QTL) with broad race-nonspecific resistance also exist. Much less work has been done to understand the genetics of durum wheat-tan spot interactions. Here, we evaluated a set of Langdon durum – wild emmer (Triticum turgidum ssp. dicoccoides) disomic chromosome substitution lines for reaction to four P. tritici-repentis isolates representing races 1-3 and 5 to identify wild emmer chromosomes potentially containing tan spot resistance genes. Chromosome 3B from the wild emmer accession IsraelA rendered the tan spot-susceptible durum cultivar Langdon resistant to all four fungal isolates. Genetic analysis indicated that a single dominant gene, designated Tsr7, governed resistance. Detailed mapping experiments showed that the Tsr7 locus is likely the same as the race-nonspecific QTLs previously identified in the hexaploid wheat cultivars BR34 and Penawawa. Four user-friendly SNP-based semi-thermal asymmetric reverse PCR (STARP) markers were developed that cosegregated with Tsr7 and should be useful for marker-assisted selection of resistance. In addition to 3B, other wild emmer chromosomes were shown to contribute moderate levels of tan spot resistance, and, as has been previously shown for tetraploid wheat, the Tsn1-Ptr ToxA interaction was not associated with susceptibility. This is the first report of a major dominant gene governing resistance to tan spot in tetraploid wheat.