Evidence for multiple introductions and clonality in Spanish populations of Fusarium circinatum.

Fusarium circinatum is thought to have been moved around the world with pine planting stock consisting, most probably, of infected seed. In this effort, we investigate the genetic structure of F. circinatum in Spain and globally. In total, 223 isolates were studied from five regions in northern Spain and eight countries. Eight microsatellite markers revealed 66 multilocus genotypes (MLGs). Minimum spanning network analysis of MLGs by region within Spain as well as globally, discriminant analysis of principal components, and analysis of molecular variance revealed that Spanish populations are significantly differentiated and structured into two distinct groups, each one including one of the dominant genotypes observed. This result suggests that two independent introductions occurred into Spain that subsequently underwent clonal divergence and admixture. This result is further supported by the linkage disequilibrium and clonality observed for F. circinatum populations in northern Spain. The maintenance of differentiation between the clusters could result from the lack of or rare sexual reproduction in Spain. Possible introduction pathways from other countries and subsequent routes of dispersion of F. circinatum in Spain are discussed.