Mycelium of a clone ofThanatephorus cucumeris(Frank) Donk (Rhizoctonia solaniKuuml;hn) produced ether-soluble substances which, when incorporated into water agar, caused basidiospores to shift from germ tube development to repetition. Repetition activity was localized in chromatograms by bioassay. Germ tubes less than 48 hours old produced ballistospores when transferred from water agar to fruiting cultures. Cells of older hyphae had apparently lost this capacity. Repetition spores, and ballistospores produced by germ tubes, were uninucleate and gave rise to cultures typical of the parent fungus. The relevance of repetition to survival and to phylogeny was discussed.
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