Genetic structure and population diversity in the wheat sharp eyespot pathogen Rhizoctonia cerealis in the Willamette Valley, Oregon, USA

Abstract

Wheat sharp eyespot, caused by the soilborne basidiomycete fungus Rhizoctonia cerealis group D subgroup I (AG‐DI), is a common disease of wheat stems that has increased in global importance in recent years. The disease caused a severe and extensive epidemic throughout the Willamette Valley of Oregon in 2014 and has remained one of the most important wheat diseases in this region subsequently. The population structure of this pathogen is still not well understood. In this study, 572 pure cultures of R. cerealis AG‐DI were isolated from five commercial fields and two experimental fields in the Willamette Valley, Oregon, in the spring of 2017 and 2018. Population structure studies were conducted using six microsatellite markers. Polymorphisms were observed at all six loci, and all seven subpopulations showed moderate gene and genotype diversity. Most of the loci were in Hardy–Weinberg equilibrium in the subpopulations, the entire population combined over locations and five of seven subpopulations were in gametic equilibrium, and the AMOVA and Mantel’s test demonstrated no differentiation among subpopulations. Though direct evidence is currently lacking, these results suggest that the sexual stage of the pathogen may be having a significant impact on pathogen population structure, and that the presence of basidiospores could be contributing to the extensive spread of this disease in the Willamette Valley in recent years.

Near telomere-to-telomere nuclear phased chromosomes of the dikaryotic wheat fungus Rhizoctonia cerealis

“…The SNP density between the A and B genome was much smaller than the SNP variation among isolates (229,003 vs 808,864), which indicated that free recombination occurred. Although no sexual stage has been found in the field or the laboratory 37 , it is hard to explain without sexual reproduction why existed high genetic and genotypic diversity in the field both emerged in this and previous studies 38, 39 . Paired clones collected in a different year and from distant fields indicated that asexual reproduction likely occurs and might play an important role in the disease.…”

Genetic Diversity and Population Genetic Structure of Setosphaeria turcica From Sorghum in Three Provinces of China Using Single Nucleotide Polymorphism Markers

“…Nei’s I varied from 0 to 1, Nei’s D ranged from 0 to infinity. The closer the Nei’s I value was to 1, the higher the genetic similarity between the two populations will be; and the larger the Nei’s D value, the greater the genetic distance between the two populations will be ( Liu and Mundt, 2020 ). Among the three groups, Henan/Shanxi had the lowest Nei’s D values, and Henan/Shaanxi had the highest values.…”

Population structure and mixed reproductive strategies in Bipolaris maydis from single and multiple corn cultivars in Fujian Province, China

“…In addition, asexual reproduction is beneficial to rapid growth and expansion. This challenge warrants the utilization of management strategies to prolong the service life period of these control methods ( Liu and Mundt, 2020 ). Furthermore, the results in this study also showed that neither geographical origins nor corn cultivars have an impact on reproductive strategy of B. maydis populations.…”

“…A reasonable interpretation of this situation is that there are two different proveniences of the pathogen that undergo mixing through sexual reproduction. A mixed reproduction strategy might explain the consolidation of two genetic groups at a comparatively slow speed ( Liu and Mundt, 2020 ). The mechanisms of this inherent differentiation should be further considered, and continued genetic study of additional more samples, since such study is necessary, and will be beneficial to clarifying this controversy.…”