In artificial culture, Aureobasidium pullulans (de Bary) Arnaud produced a stimulatory effect on rhizomorph development of Armillaria mellea (Fr.) Quél. Tests were carried out on malt agar, potato dextrose agar, and a chemically defined synthetic medium. The stimulatory substance (or substances) produced by A. pullulans was extracellular, diffusible in the medium and volatile. Tests indicated that the stimulation was caused by something other than ethanol or indoleacetic acid.
The cell-free hltrate of a liquid culture of Al~reobasidil~77z pz~llz~lans (de Bary) ilrnaud contained a substance which stimulated the growth of Artnillaria lnellea (Fr.) Quel. 'l'his stimulatory effect was apparent when either rhizornorph tips or undifferentiated mycelium on water agar discs were used as inoculum, indicating an eifect 011 both rhizomorph initiation and elongation. The cell-free hltrate was shown by gas chro~natography to contain ethanol. Ethanol had an effect on the growth of 11. ?nellea similar to that of thc cell-free liltrate.Growth of A. n7ellen \vas stimulated by the presence of ethanol in the medium and the degree of stimulation was shown to be dependent on the total amount of ethanol available a t a concentration of 500 p.p.m. Ethanol added a t regular intervals as lower concentrations in the medium stimulated the growth of A.??zellen as much as orie higher initial concentration. A concentration of ethanol as low as 50 p.p.m. added daily for 14 days was more effective than an initial concentration of 700 p.p.m. in stimulating rhizomorph development of A. 7nellea.
The effect of soil moisture and the related effect of some soil-inhabiting microorganisms on the spread through soil of the root-rotting Basidiomycete Coniophora puteana were studied. A soil moisture level of 20%–25% saturation was satisfactory for the growth of C. puteana in non-sterile soil. The fungus was able to grow out from a small alder disc inoculum in the center of a petri dish and invade alder discs at the periphery of the dish. At 50% saturation and higher C. puteana was unable to grow out into the soil. In autoclaved soil the optimum 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. puteana similar to that of completely non-sterile soil. Trichoderma viride, a known antibiotic producer, was inoculated into 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, was examined 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. Some implications of the findings are discussed.
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