Genetic Diversity of Iranian AG1-IA Isolates of Rhizoctonia solani, the Cause of Rice Sheath Blight, Using Morphological and Molecular Markers

The cause of rice sheath blight, Rhizoctonia solani AG1-IA (teleomorph: Thanatephorus cucumeris), is one of the most important rice pathogens worldwide including Iran. Due to the importance of the disease and lack of knowledge on the genetic diversity of this pathogen in Iran, 25 out of 47 isolates of R. solani collected from rice paddies in northern (mostly Guilan province) Iran were examined for anastomosis grouping, colony morphology, growth rate and genetic diversity. Based on growth rate data analysis, isolates were categorized into two distinct groups with low and high growth rate. The anastomosis group of the isolates was determined using microscopic hyphal fusion examination with standard the AG1-IA tester and confirmed using AG1-IA-specific primers in 10 selected isolates in which a single band of 265 bp was amplified. Genetic diversity was estimated among 25 isolates using inter simple sequence repeats (ISSR) and enterobacterial repetitive consensus (ERIC) analysis. DNA bands of four ISSR and a pair of ERIC primers ranged from 0.25 to 3 Kb in all isolates. Cluster analysis of the resulting data were performed using the Unweighted Pair-Group Method with Arithmetic Average method, Jaccard`s coefficient and NTSYS-pc software. The resulting dendrogram categorized the isolates into two groups with low and high growth rates at the 36% similarity level. At 80% similarity level, the isolates were categorized into 24 groups, which indicated a high genetic diversity of rice sheath blight fungus as revealed by ISSR and ERIC primers. Whereas the results of molecular analysis showed the correlation between isolates sclerotial size and growth rates, there was no correlation between genetic diversity, pathogenicity and geographical origins of isolates. While the results of molecular analysis categorized isolates into two distinct groups, which were superimposed on two groups of low and high growth rate isolates, no correlation was observed between genetic diversity, pathogenicity and geographical origins of isolates.