Transmission of the M2 double-stranded RNA in Rhizoctonia solani anastomosis group 3 (AG-3)

Abstract

Horizontal transmission of the 3.57 kb M2 double-stranded RNA (dsRNA) between mycelia of somatically incompatible isolates of Rhizoctonia solani anastomosis group 3 (AG-3), an economically important pathogen of cultivated plants in the family Solanaceae, was investigated. Nine donor isolates of R. solani AG-3 containing the M2 dsRNA were paired on potato-dextrose agar with each of three different recipient isolates where the M2 dsRNA was absent. Reverse-transcription PCR (RT-PCR) was used to detect horizontal transmission of the M2 dsRNA via hyphal anastomosis from donor to recipient isolates by examining hyphal explants taken 3 cm from the hyphal interaction zone. PCR-RFLP genetic-based markers of two nuclear loci and one mitochondrial locus were used to confirm identity and transmission between donor and recipient isolates of R. solani AG-3. The frequency of transmission observed between 72 pairings of the eight donor and three recipient isolates was approximately 4% of the total pairings, and differences in the phenotype of the recipient isolates after acquisition of the M2 dsRNA via horizontal transmission were observed. To our knowledge this represents the first demonstration of transmission of dsRNA between genetically different individuals of R. solani confirmed with nuclear and mitochondrial markers. These results suggest that transmission can occur between somatically incompatible isolates of R. solani AG-3 but that maintenance of the dsRNA in the recipient isolates was not stable after repeated subculturing on nutrient medium.

• Basidiomycete
• horizontal transmission
• mitochondrial markers
• mycovirus
• nuclear markers

We thank Dr Stellos M. Tavantzis (University of Maine, Department of Biological Sciences) for help and encouragement in the development of this research project. The authors also thank Dr Kelly Ivors (NCSU, Department of Plant Pathology) for sampling and providing tomato isolates of R. solani AG-3. We also thank Dr Takeshi Toda (NCSU, Department of Plant Pathology) for technical assistance. This research was supported by USDA CSREES grants (2004-35400-14429; 2005-34500-15893; and 2006-35604-16666) and by a grant from the North Carolina Potato Growers Association.