Genetic structure of a population of Rhizoctonia solani AG 2-2 IIIB from Agrostis stolonifera revealed by inter-simple sequence repeat (ISSR) markers

Rhizoctonia solani anastomosis group (AG) 2-2 IIIB is an important pathogen of creeping bentgrass (Agrostis stolonifera) worldwide. Limited information is currently available concerning levels of genetic diversity and population structure within this pathogen on creeping bentgrass. Twenty-three isolates were obtained from 17 symptomatic patches of a creeping bentgrass field at the Guelph Turfgrass Institute, Ontario. Anastomosis grouping was identified on the basis of morphological and cultural characteristics, and by PCR amplification using specific primers. The population structure was analyzed using five inter-simple sequence repeat (ISSR) primers, which generated 34 polymorphic loci out of 50 band positions. Distance analysis with the unweighted pair group method using arithmetic averages (UPGMA) resulted in a dendrogram which clustered the 23 isolates into four main groups, with genetic distances (1 -Dice coefficient of genetic similarity) ranging from 0 to 12%. This level of variation among isolates of R. solani AG 2-2 IIIB present in a small field of creeping bentgrass and even within single patches implied some level of recombination, but the distribution of ISSR haplotypes and gametic disequilibrium analyses revealed that asexual propagule movement was the dominant force in the population structure in this small area.