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

Abstract

AbstractWhole‐cell fatty acid compositions of binucleate Rhizoctonia AG‐D (R. cerealis) isolates representing subgroups 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), palmitic (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 percentage 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 differentiating AG‐D (I) and AG‐D (II) and supported previous differentiation 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.