QTL mapping of resistance to tan spot induced by race 2 of Pyrenophora tritici-repentis in tetraploid wheat

Authors: LIU, YUAN - North Dakota State University; SALSMAN, EVAN - North Dakota State University; Fiedler, Jason; HEGSTAD, JUSTIN - North Dakota State University; LIU, ZHAOHUI - North Dakota State University; Faris, Justin; Xu, Steven; ZHANG, QIJUN - North Dakota State University; LI, XUEHUI - North Dakota State University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2019
Publication Date: 11/12/2019
Citation: Liu, Y., Salsman, E., Fiedler, J.D., Hegstad, J.B., Liu, Z., Faris, J.D., Xu, S.S., Li, X. 2019. QTL mapping of resistance to tan spot induced by race 2 of Pyrenophora tritici-repentis in tetraploid wheat. Theoretical and Applied Genetics. 133:433-442. https://doi.org/10.1007/s00122-019-03474-2.
DOI: https://doi.org/10.1007/s00122-019-03474-2

Interpretive Summary: Tan spot is a major fungal disease in durum wheat. It attacks the leaves of the plant, causing round dead legions with a tan-colored spot in the center. Understanding this disease and identifying major genetic sources of resistance will facilitate the breeding of resistant cultivars and mitigate the effects of the disease. In this study we used 4 mapping populations that could be used for the identification of genetic loci contributing to tan spot resistance. Eight resistance loci we located that conferred resistance to every pathogen race we tested, and another two resistance loci were found that conferred resistance to only one pathogen race, but in a novel way. This information is important for researchers investigating the tan spot disease mechanism and breeders that are developing new durum wheat cultivars with durable resistance.

Technical Abstract: Durum is a tetraploid species of wheat and a staple food crop in the world. Tan spot, caused by the necrotrophic fungal pathogen Pyrenophora tritici-repentis (Ptr), is a major foliar disease of both durum wheat and hexaploid bread wheat. Understanding the Ptr-wheat interaction and identifying major QTL can facilitate the development of resistant cultivars and effectively mitigate the negative effect of this disease. Over 100 QTL have been discovered in hexaploid bread wheat. However, few mapping studies have been conducted in durum wheat. Utilizing resistant resources and identifying novel resistant loci in tetraploid wheat will be beneficial for the development of tan spot resistant durum varieties. In this study, we evaluated four interconnected tetraploid wheat populations for their reactions to the race 2 isolate 86-124, which produces Ptr ToxA. Tsn1, the wheat gene that confers sensitivity to Ptr ToxA, was not associated with tan spot in any of the populations. We found a total of 12 tan spot resistance QTL among three mapping populations. Eight QTL located on chromosomes 3A and 5A were detected in multiple populations and co-localized with race-nonspecific QTL identified in other mapping studies. Together, these QTL can confer high levels of resistance and can used for the improvement of tan spot resistance in both hexaploid bread and durum wheat breeding. Two QTL on chromosomes 1B and 7A, respectively, were found only in one population, RP336, when inoculated with a Ptr ToxA knockout strain 86-124'ToxA only, indicating their association with tan spot induced by other unidentified NEs, but under the absence of Ptr ToxA. Given the complex Ptr-wheat interaction, the removal of dominant susceptibility genes combined with integrating major race-nonspecific resistance loci should be an efficient and effective way to improve tan spot resistance.