Studies on vicissitude of Rhizoctonia solani Kühn in soil

Abstract

The competitive saprophytic ability of Rhizoctonia solani Kuhn was compared among three different strains: i.e., isolate F-16 which belongs to the spring strain, F-20 which belongs to the summer strain, both being obtained in the previous experiments (Ui et al, 1963), and B-5, a sugar beet strain which causes damping off of sugar beet seedlings and root rot of mature plants. For the assessment of the competitive saprophytic ability, the Cambridge method (Butler, 1955) and it's agar plate modification (Rao, 1959) were adopted. The substrate for saprophytic colonization of the inoculant were mature flax stem pieces and water agar plate respectively. From the results, as illustrated in the figures presented, F-20 may be regarded as a vigorous saprophyte, followed by B-5 and F-16. When the same estimations were applied to the soil-inoculum mixtures which were previously incubated for two weeks at room temperature before the addition of substrates, the saprophytic ability of F-20 showed little changes, while that of B-5 and F-16 decreased, particularly the latter behaved as a poor saprophyte. From the results of the experiments, the authors concluded as follows: R. solani has been regarded as one of the typical soil-inhabiting fungi, whereas some of the strains such as F-16, behave as a poor saprophyte when it was previously incubated for several days under competition of soil micro-organisms without a suitable substrate for colonization.