Submitted to: Society for Advancement in Plant Protection
Publication Type: Popular Publication
Publication Acceptance Date: January 20, 2006
Publication Date: January 29, 2006
Citation: Lakshman, D. 2006. Double-stranded RNA-mediated hypovirulence of Rhizoctonia solani. Association for Advancement in plant protection Newsletter (India). 1:1-3. Technical Abstract: Rhizoctonia solani is a soilborne fungal plant pathogen responsible for economic losses of crops worldwide. Isolates of Rhizoctonia (anastomosis group 3) cause a disease commonly known as black scurf, stem and stolon canker of potato. We observed that some isolates of the pathogen lose their ability to cause severe disease, a phenomenon called hypovirulence. We also demonstrated that hypovirulent isolates could protect potato crop from the effects of virulent (disease-causing) isolates of the fungus. Our research group (University of Maine and USDA-ARS) determined that both virulence and hypovirulence (reduced ability to cause disease) of some Rhizoctonia isolates are associated with the presence of distinct virus-like double-stranded RNA (dsRNA) molecules in the fungus. Genome of both the dsRNAs had been sequenced and characterized. We noted that the presence of the hypovirulence associated dsRNA causes the quinic acid (QA) biosynthetic pathway of Rhizoctonia to be active at all times. In pathogenic isolates of the fungus, the QA biosynthetic pathway is normally inactive, but can be induced by QA which is present in the soil from decaying of lignin rich organic materials. Increased activity in the QA pathway results in decreased activity in the shikimic acid pathway and the concomitant reduction of phenylacetic acid (PAA) released by the fungus. PAA is a pathotoxin of Rhizoctonia disease development. Current research at the USDA-ARS is focused on metabolites and Rhizoctonia gene(s) involved in the regulation of virulence. Increased understanding of the disease interaction will aid in protection of plants against disease caused by this plant pathogenic fungus.