Population structure comparison of the wheat sharp eyespot pathogen Rhizoctonia cerealis collection from USA and...

Sharp eyespot of wheat, caused by the basidiomycete Rhizoctonia cerealis AG-DI, is an economically important stem disease that occurs in several wheat-producing regions worldwide. However, population-genetic studies of this pathogen have thus far been restricted to individual countries, and cross-continental comparisons remain lacking. In this study, we jointly analyzed ten previously characterized R. cerealis populations comprising 850 isolates collected from China and the United States. Chinese populations exhibited substantially higher genetic diversity, a larger number of alleles, and more private alleles than U.S. populations, yet showed lower levels of sexual reproduction. Strong gene flow was detected within each country, whereas gene flow between countries was extremely limited, indicating that the two regional lineages do not share a direct ancestral origin. Because of long-term geographic separation, distinct substructures were observed within each country, with little correspondence between the subclusters of the two regions. These findings provide the first cross-continental assessment of R. cerealis population structure and offer new insights into the global evolutionary dynamics of this important wheat pathogen.