Pyrenophora tritici-repentis race 4 isolates cause disease on tetraploid wheat

Authors: GUO, JINGWEI - North Dakota State University; SHI, GONGJUN - North Dakota State University; KALIL, AUDREY - North Dakota State University; FRISKOP, ANDREW - North Dakota State University; ELIAS, ELIAS - North Dakota State University; Xu, Steven; Faris, Justin; LIU, ZHAOHUI - North Dakota State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2020
Publication Date: 9/28/2020
Citation: Guo, J., Shi, G., Kalil, A., Friskop, A., Elias, E., Xu, S.S., Faris, J.D., Liu, Z. 2020. Pyrenophora tritici-repentis race 4 isolates cause disease on tetraploid wheat. Phytopathology. 110:1781-1790. https://doi.org/10.1094/PHYTO-05-20-0179-R.
DOI: https://doi.org/10.1094/PHYTO-05-20-0179-R

Interpretive Summary: Tan spot is a serious fungal disease of both durum wheat and bread wheat wherever these crops are grown. One strain of the tan spot fungus known as race 4 was previously thought to not have the ability to cause disease on wheat, but only a few related grasses. Here, we found that race 4 can cause serious tan spot disease on many durum wheat varieties, but not bread wheat varieties. Genetic analysis was used to identify regions of the durum wheat genome that likely contain genes that govern susceptibility to race 4. This work provides useful information and molecular tools for the development of tan spot resistant durum wheat varieties.

Technical Abstract: The ascomycete fungus Pyrenophora tritici-repentis is the causal agent of tan spot of wheat. The disease can occur on both common wheat (Triticum aestivum L.) and durum wheat (T. turgidum ssp. durum) and has potential to cause significant yield and quality losses. The fungal pathogen is known to produce necrotrophic effectors (NEs) that act as important virulence factors. Based on the NE production and virulence on a set of four differentials, P. tritici-repentis isolates have been classified into eight races. Race 4 produces no known NEs and is avirulent on the differentials. From a fungal collection in North Dakota, we identified several isolates that were classified as race 4. These isolates caused no or little disease on all common wheat lines including the differentials; however, they were virulent on some durum cultivars and tetraploid wheat accessions. Using two segregating tetraploid wheat populations and QTL mapping, we identified several genomic regions significantly associated with disease caused by two of these isolates, some of which have not been previously reported. This is the first report that race 4 is virulent on tetraploid wheat, likely utilizing unidentified NEs. Our findings further highlights the insufficiency of the current race classification system for P. tritici-repentis.