Determination of whole-cell fatty acid profiles for the characterization and differentiation of isolates of Rhizoctonia solani AG-4 and AG-7

Fatty acid methyl esters (FAMEs) of isolates of Rhizoctonia solani AG-4 and AG-7 were characterized by gas chromatography and analyzed with Microbial Identification System software. Palmitic, stearic, and oleic acids were com mon in all isolates from both anastomosis groups (AGs) and accounted for 95 % of the C14 to C18 fatty acids present. Oleic acid, most common in both R. solani AG-4 and AG-7 isolates, accounted for the greatest percentages of t otal FAMEs. The presence, quantities, or absence of individual fatty acids could not be used for distinguishing AG-4 and AG-7 isolates. Anteisopentade canoic and 9-heptadecanoic acids, however, were specific to all three AG-7 isolates from Japan but absent in other AG-7 isolates and all AG-4 isolates . Pentadecanoic acid occurred in only two of the R. solani AG-4 isolates, b ut was not found in any of the AG-7 isolates. The AG-4 isolates could be di stinguished from AG-7 isolates when quantities of FAMEs and key FAME ratios were analyzed with cluster analysis and principle components were plotted. Isolates of AG-7 from Arkansas, Indiana, and Georgia appeared to be more c losely related to each other than to AG-7 isolates from Japan and Mexico. T hese differences in FAMEs were sufficiently distinct that isolate geographi cal variability could be determined. A dendrogram analysis cluster construc ted from the FAMEs data showed results similar to that of the principal com ponent analysis. Euclidean distances of total AG-4 isolates were distinct f rom total AG-7 isolates. The Arkansas and Indiana AG-7 isolates had a simil ar Euclidean distance to each another but the percentages were different fo r the AG-7 isolates from Japan and Mexico. In conclusion, variability of th e FAMEs identified in this study would not be suitable as the main diagnost ic tool for distinguishing individual isolates of R. solani AG-4 from AG-7.