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Some interrelations of root-rotting Basidiomycetes and soil-inhabiting Fungi imperfecti Pentland, Gertrude Draper

Abstract

In the first of two parts of the investigation, the stimulation of Armiil aria mellea (Fr.) Quél., a common root-rotting fungus, by Aureobastdium pullulans (DeBary) Arnaud was studied. A. pullulans is an ubiquitous imperfect fungus, inhabiting soil and other substrates. It was shown to produce in culture a volatile, heat stable, neutral substance which stimulated the mycelial development, rhizomorph initiation and rhizomorph elongation of A. mellea. A. pullulans is the only microorganism reported so far to stimulate the growth of A. mellea. The effect of ethanol on the growth of A. mellea was similar to the effect of a cell-free filtrate from a liquid culture of A. pullulans. The cell-free filtrate was shown by gas chromatography to contain ethanol. Ethanol supplied daily as 50 ppm in a glucose-asparagine medium resulted in a ten-fold increase in the number of rhizomorphs produced by A. mellea. The effects of 3-indolylacetic acid, ɣ-(indole-3)-n-butyric acid, the sodium salt of 2,4-dichlorophenoxyacetic acid and tryptophane on the growth of A. mellea were tested, but the stimulatory effect of A. pullulans was not reproduced by them. One rhizomorph tip of A. mellea could develop an extensive rhizomorph system in autoclaved soil if the stimulatory substance produced by A. pullulans was available. In the second part of the investigation the effect of soil moisture and the related effect of some soil-inhabiting Fungi imperfecti on the spread through soil of the root-rotting Basidiomycete Coniopnora puteana (Schum. ex Fr.) Karst.were studied. A soil moisture level of 20 - 25% saturation was satisfactory for the growth of C. puteana in non-sterile soil. At this moisture level C. puteana was able to grow out from a small alder disc inoculum in the centre of a petri dish and invade alder discs at the periphery of the dish. In wetter conditions (50% saturation and higher) it was unable to grow out into the soil. In autoclaved soil the cptimum moisture level for the growth of C. puteana was between 75% and 100% saturation. Small amounts of non-sterile soil were added to autoclaved soil at different moisture levels, with an effect on the growth of C. puteanas similar to that of completely non-sterile soil. Trichoderma viride Pers. ex Fr., a known antibiotic producer, was inoculated in autoclaved soil and produced a greater inhibition of C. puteana in the wetter treatments than in drier ones. The inhibitory effect of Acti-dione (cycloheximide), an antifungal antibiotic active in the pH range 3-5, was examined in non-sterile soil end in autoclaved soil. The same concentration of antibiotic resulted in a greater inhibition of the growth of C. puteana at the higher moisture levels than at the lower ones.

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