Evaluation of Stagonospora nodorum blotch severity and Parastagonospora nodorum population structure and genetic diversity across multiple locations and wheat varieties in Virginia

Abstract

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