Comparison of Whole-Cell Fatty Acid Compositions of Isolates of Rhizoctonia solani AG 2 from Tobacco and Tulip, AG 2–1 and AG-BI

Isolates of Rhizoctonia solani AG 2 from tobacco (Ntisolates) were reported to anastomose with isolates of AG-BI in high frequency (fusion frequency [FF] ‡ 50%) compared to isolates of AG 2–1 (FF < 50%), even though mature culture and thiamine requirement of the isolates were closely similar to AG 2–1. In this study, whole-cell fatty acid compositions of Nt-isolates (four isolates), isolates of AG 2–1 (eight isolates) and AG-BI (two isolates) were compared by gas-liquid chromatography analysis. Four isolates of AG 2 from tulip (AG 2-t) were also included. Palmitic (16 : 0), oleic (18 : 1 cis9) and linoleic (18 : 2 cis9,12) acids were the three major fatty acids identified which constituted 89.6–93.4% of whole-cell fatty acid content. Myristic (14 : 0), pentadecanoic (15 : 0), palmitoleic (16 : 1 cis9), stearic (18 : 0) and linolenic (18 : 3 cis9,12) acids were present at low levels. Heptadecanoic (17 : 0) and 9-heptadecenoic (17 : 1 cis9) acids were also present in Nt-isolates and isolates of AG 2–1 but not in isolates of AG 2-t and AG-BI. With the exception of oleic acid, percentage composition of fatty acids of Nt-isolates were similar with those of isolates of AG 2–1 and AG 2-t but were different from isolates of AG-BI. Although fatty acid compositions of Nt-isolates and isolates of AG 2–1 were qualitatively and quantitatively similar, principal component and cluster analyses based on all detected fatty acids showed separation of the former from the latter groups indicating that Nt-isolates are a homogenous population in AG 2–1. Additionally, isolates of AG 2-t were closely related to isolates of AG 2–1. Isolates of AG-BI were distinctly separated from isolates of AG 2–1, AG 2-t and Nt-isolates. Results of fatty acid analysis support the designation of Nt-isolates as a memberof AG 2–1 based on sequence similarity of rDNA-ITS.