Abstract

Principal component analysis (PCA) of cellular fatty acids extracted from cultures of Gaeumannomyces spp., Rhizoctonia solani(anastamosis groups AG4 and AG8) and Pythium spp. showed strong clustering of cultures within genera and good discrimination between genera. PCA of the fatty acid profiles was successful in distinguishing between seven different Pythium spp. tested (P. arrhenomannes, P. australe, P. echinulatum, P. irregulare, P. ostracodes, P. spinosum and P. ultimum) but did not distinguish between the Gaeumannomyces spp. (G. graminis var. avenae, G. graminis var. graminis, G. graminis var. tritici, G. cylindrosporusand G. incrustans ) nor the isolates of the two AG groups of Rhizoctonia examined. Significant differences between species were detected in the relative amounts of individual fatty acids. The presence of two fatty acids (20:4ω6c and 20:5ω3c), found only in the Pythium species examined, was used to detect the presence of P. echinulatum and P. irregularein wheat roots infected with these two fungi.