COMPARATIVE RESPONSE OF TWO SAPROPHYTIC AND TWO PLANT PARASITIC SOIL FUNGI TO TEMPERATURE, HYDROGEN-ION CONCENTRATION, AND NUTRITIONAL FACTORS

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Abstract
The behavior of two soil saprophytes, Trichoderma viride and Trichocladium asperum, and two root-infecting fungi, Ophiobolus graminis and Fomes annosus, was compared under various conditions in laboratory culture.On an agar-solidified organic medium optimum temperatures for growth were approximately: T. viride 25–30 °C, T. asperum 20–25 °C, O. graminis 20–25 °C, F. annosus 25 °C. T. viride rapidly outgrew the other fungi in the optimum range but this relationship changed at lower temperatures, its growth rate being equalled by that of O. graminis at 10 °C. T. viride was the only fungus to grow at 35 °C. In a synthetic liquid medium adjusted to pH values from 3.0–7.0 with a citrate–phosphate buffer, growth of O. graminis and F. annosus was sharply reduced at pH values below 5.0. T. viride made good growth at pH 3.1 and reduction in growth of T. asperum occurred only below pH 4.0. Both parasites required thiamine for growth in a synthetic medium and O. graminis also required biotin; in addition they showed a preference for organic as opposed to inorganic nitrogen sources. T. viride and T. asperum grew well with KNO3 as nitrogen source and neither required vitamins. D-Glucose, D-fructose, and D-mannose were readily utilized, and D-arabinose poorly utilized, by all four fungi. Utilization of other hexoses, pentoses, disaccharides, and polysaccharides varied considerably between the fungi.The relationship of the results obtained to the observations of others on the ecology of soil fungi is discussed and the possibility that combinations of physical and nutritional factors may favor specific fungi in the soil is considered.