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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #328622

Research Project: Mitigating Alternate Bearing of Pecan

Location: Fruit and Tree Nut Research

Title: Population structure and genetic diversity of Fusicladium effusum in the USA

Author
item Bock, Clive
item Hotchkiss, Michael - Mike
item Stevenson, Katherine - University Of Georgia
item Wood, Bruce

Submitted to: National American Phytopathology Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 5/16/2016
Publication Date: 12/1/2016
Citation: Bock, C.H., Hotchkiss, M.W., Stevenson, K.L., Wood, B.W. 2016. Population structure and genetic diversity of Fusicladium effusum in the USA [abstract]. National American Phytopathology Meetings. 106-S:S4.138.

Interpretive Summary: 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 was =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.

Technical Abstract: 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 was =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.