Grouping of Binucleate Rhizoctonia Anastomosis Group D (AG-D) Isolates into Subgroups I and II Based on Whole-Cell Fatty Acid Compositions

Whole-cell fatty acid compositions of binucleate Rhi- zoctonia AG-D (R. cerealis) isolates representing sub- groups I [AG-D (I)] and II [AG-D (II)] obtained from various host plants were compared. Ten fatty acids including myristic (14 : 0), pentadecanoic (15 : 0), pal- mitic (16 : 0), palmitoleic (16 : 1 cis9), heptadecanoic (17 : 0), 9-heptadecenoic (17 : 1 cis9), stearic (18 : 0), oleic (18 : 1 cis9), linoleic (18 : 2 cis9,12) and linolenic (18 : 3 cis9,12) were consistently present in all isolates of Rhizoctonia AG-D. The major fatty acids found were palmitic, oleic and linoleic acids, comprising 88±93% of the whole-cell fatty acid content. The remaining fatty acids were present in smaller amounts ranging from 0.01 to 5.03% of the whole-cell fatty acid content. Palmitic and oleic acids were present in approximately two and three times higher concentrations in isolates of AG-D (I) than in isolates of AG-D (II), respectively. On the other hand, linoleic acid was about two times lower in isolates of AG-D (I) than in isolates of AG-D (II). Principal component and cluster analyses of the per- centage composition of fatty acids showed distinct separation between AG-D (I) and AG-D (II). The results indicated that fatty acid analysis is useful for di€erentiating AG-D (I) and AG-D (II) and supported previous di€erentiation of the two subgroups on the basis of cultural characteristics, pathogenicity and DNA analyses. In addition, a Rhizoctonia AG-Q isolate from bentgrass and Rhizoctonia AG-D isolates causing foot rot of wheat and stem rot of mat rush were grouped in AG-D (I), based on the percentage composition of fatty acids.