Population structure and genetic diversity in Virginia populations of Parastagonospora nodorum infecting wheat

Authors: KAUR, NAVJOT - Virginia Tech; Mehl, Hillary; LANGSTON, DAVID - Virginia Tech; HAAK, DAVID - Virginia Tech

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2023
Publication Date: 2/7/2024
Citation: Kaur, N., Mehl, H.L., Langston, D., Haak, D. 2024. Population structure and genetic diversity in Virginia populations of Parastagonospora nodorum infecting wheat. Phytopathology. 114:258-268. https://doi.org/10.1094/PHYTO-10-22-0392-R.
DOI: https://doi.org/10.1094/PHYTO-10-22-0392-R

Interpretive Summary: Stagonospora nodorum blotch (SNB) is a foliar fungal disease of wheat caused by Parastagonospora nodorum. SNB can cause significant loss of wheat grain yield in Virginia and the surrounding mid-Atlantic region. Genetic diversity in both the crop host and the pathogen can influence the effectiveness of disease management approaches including deployment of host resistance. The objective of this study was to characterize genetic diversity in Virginia populations of P. nodorum and determine if wheat varieties varying in susceptibility to SNB are infected with different genetic types of the fungal pathogen. Fungal populations were genetically diverse across locations and wheat cultivars, but there was little to no evidence of P. nodorum adapting to different environments or wheat varieties varying in susceptibility to SNB. Understanding genetic diversity within plant pathogen populations and how genotypes respond to different hosts and environments is critical for developing long-term disease management tactics that will minimize crop losses.

Technical Abstract: Parastagonospora nodorum is a necrotrophic pathogen that causes Stagonospora nodorum blotch (SNB) in wheat. Wheat varieties grown in Virginia vary in susceptibility to SNB, and the severity of SNB varies across locations and years. However, the impacts of wheat genetic backgrounds and environments on SNB severity and the structure of P. nodorum populations in the region have not been well studied. Thus, a population genetic study was conducted utilizing P. nodorum isolates collected from different wheat varieties and locations in Virginia. A total of 320 isolates were collected at seven locations over 2 years from five wheat varieties. Isolates were genotyped using multilocus simple sequence repeat markers, and necrotrophic effector (NE) and mating type genes were amplified using gene-specific primers. Wheat varieties varied in susceptibility to SNB, but site-specific environmental conditions were the primary drivers of disease severity. Fungal populations were genetically diverse, but no genetic subdivision was observed among locations or varieties. The ratio of the two mating type idiomorphs was not significantly different from 1:1, consistent with the P. nodorum population undergoing sexual reproduction. Three major NE genes were detected within the P. nodorum population, but not with equal frequency. However, NE gene profiles were similar for groups of isolates originating from different varieties, suggesting that wheat genetic backgrounds do not differentially select for NEs. There was no evidence of population structure among P. nodorum populations in Virginia and, thus, no support for wheat genetic backgrounds shaping these populations. Finally, although varieties only exhibited moderate resistance to SNB, current levels of resistance are likely to be durable over time and remain a useful tool for integrated management of SNB in the region.