A Study of the Epiphytic Growth Habit of Fomes annosus

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Abstract
On pine roots in calcareous soils Fomes annosus grows epiphytically among the bark scales, but on roots in acidic soils this does not occur. It appears that this is the result of a natural micro-biological control operating only under acidic conditions. However, studies of Trichoderma spp., fungi thought to be representative of the antagonistic microflora, showed them to be more abundant on roots in alkaline soil than on those in acidic soil. By means of a new classification of the genus, the Trichoderma isolates were analysed and a clear differentiation between the isolates from the two types of site was discovered. T. viride Pers. ex S. F. Gray was the most common of the green-spored isolates on roots from acidic sites and T. hamatum Rifai on those from alkaline. With the hyaline-spored isolates an almost complete separation was found between T. pilulferum Rifai and Webster on acidic sites and T. polysporum (Link ex Pers.) Rifai on alkaline. An agar-plate technique designed to study the interaction of F. annosus and the root surface fungi in a neutral environment showed a slightly higher level of antagonism on the part of fungi from alkaline sites and this appeared to be mainly due to the activity of Trichoderma spp. and other fast-growing species. A second agar-plate technique was devised to study the effect of pH on antibiotic activity. By no means all the species studied showed activity under the conditions of test, Trichoderma spp. and Cylindrocarpon radidcola being the most effective. Among these there was a high degree of adaptation to environment, with acidic isolates having their most powerful effect at pH 4.0 and alkaline isolates at pH 7.0. Consequently no support was obtained for the hypothesis that a direct pH effect could limit antagonism between root surface fungi and F. annosus, although the results did provide evidence for the ecological importance of antibiotics. A study of the tolerance of a number of F. annosus isolates to the antibiotics produced by several antagonists gave no indication that strains of the parasite isolated from trees killed on calcareous sites were particularly adapted to tolerate antibiotics produced at high pH values. The only isolates to behave exceptionally were two from New Zealand which appeared to have a distinctly lower competitive saprophytic ability than the others.

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