Effects of kinetin and related compounds on growth and sexual reproduction of Saprolegnia australis.

An isolate of Saprolegnia australis grew readily and produced abundant sex organs on a chemically defined medium. The optimal temperature for growth was higher (25°) than the optimal temperature for sexual reproduction (20°). Addition of the purines, adenine and hypoxanthine to the medium stimulated production of oogonia while addition of kinetin and 6-benzylaminopurine inhibited this process. When kinetin and adenine were added together, the two purines interacted in affecting oogonial production, and adenine overcame the inhibitory action of kinetin. It is suggested that purines may play some specific role in the synthesis of one or more of the hormones which probably initiate sexual reproduction in S. australis and that kinetin and 6-benzylaminopurine may inhibit hormone synthesis. Two other growth regulators of higher plants, indol-3-ylacetic acid and gibberellic acid, did not affect development of the fungus. No evidence was found to suggest that S. australis was producing any substance with cytokinin activity.