Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 5, 2009
Publication Date: August 1, 2009
Citation: Baumgartner, K., Fujiyoshi, P.T., Bergemann, S., Travadon, R. 2009. LIMITED POPULATION STRUCTURE OF ARMILLARIA MELLEA THROUGHOUT COASTAL CALIFORNIA SUGGESTS GENE FLOW THROUGH BASIDIOSPORE DISPERSAL. Phytopathology. 99:S9. Technical Abstract: Armillaria mellea is a fungal pathogen in the orchards, forests, and urban areas of California (CA). Diploid mycelia spread vegetatively belowground among host roots. Basidiospores are not thought to infect planted hosts and haploid mycelia are not collected in nature. We tested the hypothesis that A. mellea populations are spatially structured, based on an assumed limited capacity for spore dispersal. Collections were made from forests and urban areas at five locations (from North to South: St. Helena-N, St. Helena-S, Berkeley, San Jose, Los Angeles), separated by linear distances of 0.3, 80, 78, and 500 km (658 km total). A total of 59 isolates, representing 59 somatic incompatibility groups, were genotyped with nine microsatellite loci. Global differentiation across locations was insignificant (FST=0.011, P>0.05). Pairwise comparisons of locations revealed significant genetic differentiation (FST=0.008, P<0.05) between only the most distant locations (St. Helena-N v. Los Angeles). Assignment tests in STRUCTURE grouped isolates from all locations into one cluster. Our findings of limited population subdivision and no geographic clustering of isolates suggest that spore dispersal prevents geographic differentiation, with the exception of somewhat limited gene flow between opposite ends of CA. The existence of one contiguous, interbreeding population is consistent with the presence of a relatively continuous range of hosts between northern and southern CA.