P-555 - Population structure and cryptic recombination of Xylaria necrophora, an emerging pathogen of soybean in the southern United States

Xylaria necrophora is an emerging root-associated pathogen of soybean in the southern United States, causing a disease known as taproot decline (TRD). The recent emergence of this pathogen in the region represents an important new threat to soybean production. While our understanding of the pathogen has improved in the last decade, questions about its biogeographical history and reproductive strategies remain unanswered. Here, we attempted to address these questions by performing Illumina sequencing of 160 representative isolates from the known geographical range (AL, AR, LA, MS, and TN). Using a matrix of 148,520 single nucleotide polymorphisms (SNPs), we tested the hypothesis that genetic diversity is consistent with patterns of isolation-by-distance (IBD). Additionally, we compared the Index of Association (IA) among loci and between populations to assess recombination strategies. Bayesian clustering of individuals in Structure suggest the data best-fit 4 populations and Discriminant analysis of principal components (DAPC) suggested population structure by state, with significant overlap between AL-MS, AR-MS, and LA-MS, consistent with weak genetic IBD. Comparisons of IA among populations and between simulated populations ranging from clonal to sexual suggested cryptic recombination. These findings support the hypothesis that X. necrophora populations found in the region are somewhat geographically isolated with evidence of ongoing gene flow and that cryptic recombination may increase the evolutionary potential for the pathogen to adapt to diverse management approaches.