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Poster: Epidemiology: Population Biology Genetics


Population structure and genetic diversity of Fusicladium effusum in the USA
C. BOCK (1), M. Hotchkiss (2), K. Stevenson (3), B. Wood (4) (1) USDA/ARS SE Fruit & Tree Nut Research Laboratory, 21 Dunbar Rd., U.S.A.; (2) USDA-ARS SE Fruit and Tree Nut Research Laboratory, U.S.A.; (3) Department of Plant Pathology, University of Geor

Scab (Fusicladium effusum) is the most destructive disease of pecan in the Southeast US. Infection is thought to occur solely through asexually produced conidia. To explore the population structure and genetic diversity of F. effusum, populations were hierarchically sampled from 11 orchards in Alabama, Florida, Georgia, Illinois, Kansas, Louisiana, Mississippi, Oklahoma and Texas. A total of 734 isolates was collected from up to 20 leaves from each of 3 to 6 trees in each orchard. Isolates were screened against 30 microsatellite markers. Polymorphic loci per population were ≥96.7%. Populations were genetically diverse (Nei’s measure of genetic diversity = 0.505-0.692). An analysis of molecular variance showed 81% of variation occurred in the populations of F. effusum within trees, 3% in populations between trees within orchards, and 16% between orchards. Population differentiation was low (GST = 0.17) and gene flow relatively high (Nm=2.5). However, there was some association between population genetic and log physical distance (r=0.471, P=0.0003). Ten of the 11 populations showed evidence of gametic disequilibrium (r?d = 0.024-0.057), which might be explained by a predominance of within-season asexual reproduction, or possibly by founder effects or migration rates. The results show that F. effusum is a genetically diverse pathogen, with the degree and distribution of genetic diversity often associated with sexual recombination.