PRELIMINARY STUDIES ON THE SEXUAL STAGE OF RHIZOCTONIA SOLANI KÜHN

Abstract

The perfect stage of a flax strain of Rhizoctonia solani Kühn was obtained fairly consistently on artificial media. In growth characters and morphological dimensions, it agreed closely with those of Pellicularia filamentosa (Pat.) Rogers, except that its sterigmata averaged three times as long (26 μ). This latter character suggests close relationship to Corticium praticola Kotila. Single-basidiospore cultures differed among themselves and from the parent strain in morphology, cultural characters, growth rates, and pathogenicity on Royal flax. Some single-spore cultures produced the perfect stage, although preliminary pairings of sterile single-spore cultures remained sterile. This isolate is thus heterozygous and homothallic. There appear to be 12 chromosomes in the diploid nucleus in the basidium. The mature basidiospore is predominantly uninucleate; occasionally a binucleate basidiospore is observed. Germination is by repetition on plain agar, or by germ tubes on rich media. Those basidiospores which germinate by repetition are commonly uninucleate and give rise to uninucleate secondary basidiospores. Basidiospore discharge is by the drop excretion mechanism. To determine the identity of the flax strain, it will be necessary to produce the perfect stage of the flax strain on natural substrates or the perfect stage of P. filamentosa on artificial media.