A Simplified Branching Assay for Rhizoctonia solani

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Abstract
Two different measures of branching, the Internode Length Unit (ILU) and the Hyphal Growth Unit (HGU), were applied to Rhizoctonia solani Kuhn, AG4. The ILU (the mean length in .mu.m of 10 internodes) was simple to perform and yielded consistent results. Results using this measure and the HGU (the mean length of mycelium per hyphal tip) as a measure of branching were compared. Growth of R. solani on media containing different carbon sources or on different concentrations of sucrose or glucose all yielded ILU of ca. 200-225 .mu.m; thus branching was not affected by these treatments. Internode lengths were also constant over 29 hours for entire colonies of R. solani. The hypae were more highly branched (mean ILU = 134 .mu.m) when the fungus was grown with cellophane interposed between the mycelium and the culture medium. Hyphae aligned in the grooves of scored Parafilm were more highly branched (ILU = ca. 165 .mu.m) than hyphae on smooth Parafilm (ILU = ca. 300 .mu.M); these branching frequencies were not affected by the presence of a nutrient medium. The Internode Length Unit is a simple, repeatable, and descriptive unit for measurement of lateral branch production in Rhizoctonia solani.