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Rhizomorph Initiation and Growth in Armillaria mellea Promoted by o-Aminobenzoic and p-Aminobenzoic Acids. M. O. Garraway, Assistant Professor, Department of Plant Pathology, The Ohio State University, Columbus 43210. Phytopathology 60:861-865. Accepted for publication 16 December 1969. DOI: 10.1094/Phyto-60-861.

o-Aminobenzoic acid (anthranilic acid or AA) and p-aminobenzoic acid (PABA) promoted rhizomorph initiation and growth in Armillaria mellea after 5 weeks on a glucose-l-asparagine medium containing 10 ppm of either aromatic. Several other biosynthetically related aromatic compounds promoted only mycelial growth. Cultures of A. mellea grown for 7 days on a medium supplemented with 500 ppm ethanol continued to produce rhizomorphs after transfer to a fresh medium containing AA or PABA or both. After 21 days, however, there was more rhizomorph growth on media containing 5, 10, or 20 ppm AA than on media containing comparable concentrations of PABA. Rhizomorph growth of cultures transferred from an ethanol-supplemented medium was enhanced by the addition of 0.1 or 1.0 ppm AA to media containing 5 ppm PABA, but not by the addition of 0.1 or 1.0 ppm PABA to media containing 5 ppm AA. Indole-3-acetic acid (IAA) promoted rhizomorph initiation and growth of A. mellea after 5 weeks on a glucose-l-asparagine medium containing 10 or 20 ppm but not 1 ppm. Comparable concentrations of folic acid (FA) were ineffective. Similarly, IAA promoted rhizomorph growth of cultures that were transferred from an ethanol-supplemented medium to one containing 10 or 20 ppm. At pH 4.8 comparable concentrations of FA were ineffective, but at pH 6.0, 20 ppm FA promoted a small amount of rhizomorph growth. These data indicate that IAA is more effective in promoting rhizomorph growth than is FA, and suggest that A. mellea may be deficient in IAA when grown on a glucose-l-asparagine medium. Thus AA may possibly function as a precursor for IAA.