Inoculum potential as a factor limiting lethal action by Trichoderma viride Fr. on Armillaria mellea (Fr.) Quél

Abstract

As originally reported by D. E. Bliss, fumigation with carbon disulphide of soil containing roots infected by Armillaria mellea results in a notable increase of Trichoderma viride, which has a tolerance of carbon disulphide higher than that of most other soil fungi; the augmented population of T. viride invades the fumigated roots, but there is still an open question as to what proportion of the A. mellea mycelium is killed by direct fungicidal action of carbon disulphide and what proportion is killed by lethal action of T. viride following fumigation. The latter fungus is not the only one thus selected by fumigation; Penicillium wortmanni is still more resistant to carbon disulphide, and developed prominently on the surface of fumigated wood segments in a previous investigation. The experiment described was designed to determine whether T. viride acting on its own could kill A. mellea in woody inocula, and to what extent the lethal action of T. viride was governed by its inoculum potential in the soil. Incubation of inoculum segments for 23 days in a pure culture of T. viride, grown on autoclave-sterilized soil, resulted in a 95% kill of A. mellea; dilution of the pure culture to ¼ and ⅛ strengths with unsterilized soil caused a progressive reduction in the lethal effect of T. viride upon A. mellea. The greatest lethal activity of T. viride against A. mellea previously observed in a fumigated and then incubated soil did not exceed that produced by dilution of the pure culture of T. viride to ¼ strength in this experiment. Incubation of inocula of A. mellea in a pure culture of P. wortmanni for the same period resulted in no loss of viability, but rather in a slight increase in rate of rhizomorph growth from the inocula thus treated.