Genetic structure of South Australian Pyrenophora teres populations as revealed by microsatellite analyses

The aim of this study was to determine the genetic structure of South Australian field populations of the barley net blotch pathogens, Pyrenophora teres f. sp. teres (PTT) and P. teres f. sp. maculata (PTM), using microsatellite DNA markers. Three PTT populations (76 isolates total) and two PTM populations (43 isolates total) were sampled from separate fields during a single growing season. The results showed that of the 20 microsatellite loci examined, 17 (85%) were polymorphic within the PTT and PTM populations. In total, 120 distinct alleles were identified of which only 11 (9%) were shared between the two population types. Nei's measure of gene diversity across the PTT and PTM populations was similar at 0.38 and 0.40, respectively, and also much higher than previously reported from studies in which other types of molecular markers were used. The coefficient of genetic differentiation among both populations was the same (G(ST)=0.03) and the low and insignificant estimates of F(ST), as indicated by θ, between populations of the same type (PTT: θ<0.008, PTM: θ=0.014) indicated that isolates sampled from different areas within the same field were genetically similar. In contrast, high and significant genetic differentiation was observed among and between populations of different type (G(ST)=0.42, θ>0.567). The high number of unique multilocus haplotypes observed within the PTT (84%) and PTM (100%) populations, combined with a 1:1 distribution of both mating types, suggested that sexual reproduction was predominant among these populations. However, tests for multilocus associations showed that both PTT and PTM populations were in significant linkage disequilibrium. Although the levels of disequilibrium were low, an asexual reproductive component could not be excluded.