Worldwide genetic structure elucidates the eurasian origin and invasion pathways of dothistroma septosporum, causal agent of dothistroma needle blight

Dothistroma septosporum, the primary causal agent of Dothistroma needle blight, is one of the most significant foliar pathogens of pine worldwide. Its wide host and environmental ranges have led to its global success as a pathogen and severe economic damage to pine forests in many regions. This comprehensive global population study elucidated the historical migration pathways of the pathogen to reveal the Eurasian origin of the fungus. When over 3800 isolates were examined, three major population clusters were revealed: North America, Western Europe, and Eastern Europe, with distinct subclusters in the highly diverse Eastern European cluster. Modeling of historical scenarios using approximate Bayesian computation revealed the North American cluster was derived from an ancestral population in Eurasia. The Northeastern European subcluster was shown to be ancestral to all other European clusters and subclusters. The Turkish subcluster diverged first, followed by the Central European subcluster, then theWestern European cluster, which has subsequently spread to much of the Southern Hemisphere. All clusters and subclusters contained both mating-types of the fungus, indicating the potential for sexual reproduction, although asexual reproduction remained the primary mode of reproduction. The study strongly suggests the native range of D. septosporum to be in Eastern Europe (i.e., the Baltic and Western Russia) and Western Asia.Figure S1: Delta K plot of the STRUCTURE analysis, showing K = 3 as the best clustering of individuals, Figure S2: Bayesian clustering of D. septosporum multilocus haplotypes inferred using the program STRUCTURE at K = 6, K = 7 and K = 8 (a) and K = 9, K = 10 and K = 11 (b). Each multilocus haplotype is represented by a vertical line partitioned into colored sections that represent the isolate’s estimated membership fractions in each cluster. Black lines separate isolates from different population groups, Figure S3: Plot of the Bayesian information criterion (BIC) vs. the number of clusters from k-means clustering showing a break at K = 3, indicating three clusters best describe the dataset for DAPC analysis, Figure S4: Bayesian clustering of only the North American D. septosporum multilocus haplotypes inferred using the program STRUCTURE at K = 2, K = 3 and K = 4. Each multilocus haplotype is represented by a vertical line partitioned into colored sections that represent the isolate’s estimated membership fractions in each cluster. Black lines separate isolates from different population groups. The inset shows a graph of delta K, Figure S5: Graphical representation of the winning scenarios of demographic history for each of the eight DIYABC analyses. Abbreviations used on time scales refer to time parameters used during simulations, Figure S6: Model checking of the winning DIYABC scenarios for each of the eight conducted analyses, Table S1: Details of D. septosporum isolates used in this study including the host, geographic location, population group, microsatellite allele calls and mating-types, Table S2: Scenario descriptions, posterior probabilities with 95% credibility intervals of each scenario, and posterior predictive error of models, Table S3: Pairwise population FST (below the diagonal) and Nm, the estimated number of migrants per generation (above the diagonal) for the D. septosporum population groups, Table S4: Posterior distributions of parameters for winning scenarios of DIYABC analyses 1 to 8.The Forestry Commission, UK, by the Estonian Research Council and by the European Regional Development Fund.https://www.mdpi.com/journal/jofam2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog