Preliminary population structure analysis of Plectosporium alismatis: a potential biocontrol agent for Alismataceae weeds in Australian rice crops.

The genetic structure of Plectosporium alismatis (Oudem.) W.M. Pitt, W. Gams, & U. Braun, a pathogen of weedy species of the Alismataceae common in Australian rice crops, was investigated using primers for repetitive elements including simple sequence repeats (SSR), enterobacterial repetitive intergenic consensus (ERIC) sequences, and repetitive extragenic palindromic (REP) sequences. Forty-two isolates from 17 locations within three geographic regions in Australia were analysed. Twenty-four polymorphic loci were observed at an average of 2.7 loci per primer. Despite significant differences in the frequency of alleles at several loci, Nei's measure of genetic diversity across all loci was similar for the three regions, ranging from 0.116 to 0.268. On average, the total gene diversity across all regions was moderate to low (0.192), with diversity among and within regions accounting for 9% and just over 90% of the total diversity, respectively. The overall population differentiation (GST = 0.100) between regions was relatively small, and Nei's normalised genetic identity (I) was 0.97 for all regions across all loci, compared with the theoretical maximum of 1.00. Estimates of gene flow (Nm) ranged from approximately 1 to 1898 for individual loci. Based on a GST of 0.100 across all 24 loci, populations from the three regions are a coevolving unit. Population structure appears to be shaped by clonal reproduction, supplemented with intermittent rounds of recombination or gene flow over considerable distances. Pathogen migration probably occurs via infected seed and (or) plant material transported by irrigation channels and watercourses.