Responses of Representative Fungi to Certain Growth-Regulating Substances

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Abstract
Four filamentous fungi, Phycomyces blakesleeanus (+ strain), Aspergillus candidus, Schizophyllum commune (haplont), and Neu-rospora tetrasperma were grown in the presence of varying concns. of 4 growth-regulating substances, indole-3-acetic acid, alpha-naphthaleneacetic acid, 2,4-dichlorophenoxyacetic acid, and 2,4,5-trichlorophenoxyacetic acid. Growth responses were measured by determining linear growth rates in the presence of the different substances and in untreated controls. Effects of the substances on the different fungi were of 2 classes, stimulating and inhibiting, and were not identical for the 4 test organisms. As a general rule inhibition occurred within the concn. range 10-2 to 10-3 [image]; stimulation within the concn. range 10 3 to 10 4 [image]. The effects on growth were not constant throughout the test period. Three types of stimulation relative to time were observed stimulation during the early phases of growth; prolonged stimulation over the entire period of growth; and stimulation during the late growth phases. Effects of a series of concns. of the 4 substances were tested on conidiospores of A. candidus. Compared to the controls, the percentages of spores germinating increased in the presence of alpha-naphthaleneacetic acid, and decreased in the presence of the other 3 substances.