Statistical approach to determine the effect of combined environmental parameters on conidial development of Trichoderma atroviride (T-15603.1)

Trichoderma atroviride (T-15603.1) is a promising fungal agent for biological control of wood decay fungi in urban tree wounds. The aim of this work was to determine the combined effects of water activity (a(w), 0.998-0.892), temperature (10-30 degrees C) and pH (3-7) on the development of conidia on low-nutrient agar (LNA). Lag phase prior to germination (h), germination rates (mu(m)) and germ-tube elongation were obtained at each set of conditions. The experimental data were used to fit a response surface model for predicting the germination rates of T-15603.1 and to analyze the effect of the abiotic parameters tested. The polynomial response surface model was mathematically evaluated using graphical plots and several statistical indices (RMSE, %SEP, A(f), B-f, pRE). Data analyses showed a highly significant effect on conidial development of a(w) and temperature (P < 0.001), whereas no significant effect of pH (P >= 0.05) was observed. The germination rate dropped and the lag prior to germination increased as the temperature and a(w) decreased, but T-15603.1 appeared to be more sensitive to a(w) reduction than to temperature. The minimum a(w) level for germination was 0.910 at 15-25 degrees C, and maximum germination rates were obtained at a(w) = 0.998, 25-30 degrees C and pH 5. The response surface model was useful and widely accurate (R-2 = 0.983) for predicting the germination rate of T-15603.1 and complemented the experimental results. These findings contribute to better understanding how combined environmental factors affect the environmental parameter tolerance levels of T-15603.1 and to the development of an adequate delivery system for optimized application of T-15603.