Signatures of Global Dispersal and Population Structure In Sclerotinia Homoeocarpa.

Sclerotinia homoeocarpa incites dollar spot, a disease that causes significant economic damage to turfgrass worldwide, but its population biology is poorly understood.  The objective of this research is to infer the population structure of S. homoeocarpa on a global scale.  To date we have genotyped 1,222 S. homoeocarpa isolates, obtained from 109 locations on five continents and Oceania, at 14 microsatellite loci and for mating type.  Beyond the expected structure delimiting the C3 and C4 host type isolate clades, within each multivariate and Bayesian clustering analyses identified limited admixture and substructure that was associated with mating type and continent of origin.  In addition, analyses revealed a small group of 37 isolates that were marked by admixture and could not be classified with isolates from either C3 or C4 grasses.  Of the 650 C3 and 535 C4 host type isolates, 72% and 8%, respectively, were assigned to one of several multilocus haplotypes that were identified in isolates originating from two to six continents.  Within all but one of 136 multilocus haplotypes, all isolates were of the same mating type.  When grouped by clade and continent, clone correction showed few deviations from an equal number of MAT1-1 and MAT1-2 mating types.  Initial results from this study suggest that Sclerotinia homoeocarpa has undergone long distance dispersal followed by clonal amplification, with a possible history of sexual reproduction.

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