Abstract
Factors affecting the inactivation of Trichoderma species in soils ranging from neutral to alkaline were investigated. Even though the fungus was isolated from the pineapple field soil (pH 4.2), the most suitable pH value for spore formation was 6.0. When the fungus was incubated in buffered liquid media, the medium at pH 4.0 shifted to the alkaline side and the one at pH 8.0 shifted to the acid side, but almost no change was observed for the medium at pH 6.0. Thus the direct effect of the pH as well as indirect influence of the microorganisms in Kunigami mahji, with common parent material but differing in the pH value were investigated. Fungal activity in a vegetable field soil (pH 7.8) was about three times higher than that of the pineapple field soil (pH 4.2), four times for actinomycetes and five times for bacteria. Comparison of the antagonistic ratio of the fungi isolated from both soils against Trichoderma lignorum (RT-11), the vegetable field soil had twice as many fungi as the pineapple field soil. There were many Aspergillus species isolated from the vegetable field soil which showed a strong antagonism with T. lignorum (RT-11). Since the culture filtrate of Aspergillus spp. did not affect T. lignorum (RT-11), it was assumed that the observed antagonism was not due to mycoparasitism, lysis or antibiosis but to competition for nutrients or habitats. In conclusion, the inactivation of Trichoderma in neutral and alkaline soils was attributed to the indirect effect of soil microorganisms as well as to the direct effect of the soil pH.
