Parastagonospora nodorum and related species in western Canada: genetic variability and effector genes

Authors: HAFEZ, MOHAMED - Lethbridge Research Center; GOURLIE, RYAN - Lethbridge Research Center; DESPINS, THERESE - Lethbridge Research Center; TURKINGTON, THOMAS - Lacombe Research Centre; Friesen, Timothy; ABOUKHADDOUR, REEM - Lethbridge Research Center

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2020
Publication Date: 12/4/2020
Citation: Hafez, M., Gourlie, R., Despins, T., Turkington, T.K., Friesen, T.L., Aboukhaddour, R. 2020. Parastagonospora nodorum and related species in western Canada: genetic variability and effector genes. Phytopathology. 110:1946-1958. https://doi.org/10.1094/PHYTO-05-20-0207-R.
DOI: https://doi.org/10.1094/PHYTO-05-20-0207-R

Interpretive Summary: Septoria nodorum blotch (SNB) is a problem in wheat producing regions throughout North America. Even though this is a known pathogen, gaps remain in our understanding of the virulence factors present in the pathogen and the corresponding host susceptibility targets in any given wheat producing region. In this work, we sampled the pathogen (Parastagonospora nodorum) population in western Canada to identify what virulence factors were present in the population. We also identified whether the corresponding wheat susceptibility targets were present. This work showed that a large portion of the pathogen population harbored known virulence factors and that the corresponding wheat susceptibility targets are present in the historical collection of common wheat cultivars planted in Western Canada. This information is important for wheat geneticists and breeders involved in producing cultivars with SNB resistance. This study also provides information on the evolutionary model of this pathogen.

Technical Abstract: Parastagonospora nodorum is an important fungal pathogen that causes septoria nodorum blotch (SNB) in wheat. This pathogen produces several necrotrophic effectors that act as virulence factors; three have been cloned, SnToxA, SnTox1, and SnTox3. In this study, P. nodorum and its sister species Parastagonospora avenaria tritici (Pat1) were isolated from wheat node and grain samples collected from distanced sites in western Canada during 2018. The presence of effector genes and associated haplotypes were determined by PCR and sequence analysis. An ITS-RFLP test was developed to distinguish between leaf spotting pathogens including: P. nodorum, Pat1, Pyrenophora tritici-repentis and Bipolaris sorokiniana. P. nodorum was mainly recovered from wheat nodes and to a lesser extent from the grains, while Pat1 was exclusively isolated from grain samples. The effector genes were present in almost all P. nodorum isolates, with the ToxA haplotype 5 (H5) being most prevalent, while a novel ToxA haplotype (denoted here H21) is reported for the first time. In Pat1, only combinations of SnTox1 and SnTox3 genes were present. A ToxA haplotype network was also constructed to assess the evolutionary relationship among globally found haplotypes to date. Finally, cultivars representing wheat development in Canada for the last century were tested for sensitivity to Sn-effectors and to the presence of Tsn1, the ToxA-sensitivity gene. Of tested cultivars, 32.9% and 56.9% were sensitive to SnTox1 and SnTox3, respectively, and Tsn1 was present in 59% of the cultivars. In conclusion, P. nodorum and Pat1 were prevalent wheat pathogens in Canada with a potential specific tissue colonization capacity, while producing necrotrophic effectors to which wheat is sensitive.