Effect of pH on the growth and competition of <i>Trichoderma</i> spp. and <i>Fusarium</i> spp.

Collar rot caused by <i>Fusarium</i> spp. is a serious threat to the production of <i>Passiflora edulis</i>. However, biocontrol methods are lacking. <i>Trichoderma</i> spp., as the most widely applied biocontrol fungus, can be effective in managing crop diseases. The effectiveness is significantly influenced by environmental factors, such as soil pH. To screen potential biocontrol strains against collar rot of <i>P. edulis</i>, and to explore the effect of pH on the inhibition rate of <i>Trichoderma</i> spp., we selected four <i>Trichoderma</i> species and four <i>Fusarium</i> species isolated from <i>P. edulis</i> planting area in Xishuangbanna. The growth dynamics of different strains under different pH conditions were determined using the mycelial growth rate method. The effect of pH on the growth inhibition of <i>Fusarium</i> spp. by <i>Trichoderma</i> spp. was investigated using the plate confrontation assay. The results showed that the optimal growth pH range was 4-6 for <i>Trichoderma</i> spp. and 7-9 for <i>Fusarium</i> spp. All four <i>Trichoderma</i> strains exhibited significant inhibitory effects on the growth of the four <i>Fusarium</i> strains. <i>T. harzianum</i> showed the most notable inhibition, reaching up to a 72% inhibitory rate. Moreover, pH significantly influenced the inhibitory effect of <i>Trichoderma</i> spp., with variations observed depending on the specific species of <i>Trichoderma</i> spp. and <i>Fusarium</i> spp. Therefore, it is essential to consider the environmental pH impact on the efficacy of biocontrol agents when applying biological control measures in the field, tailored to the specific pathogen and biocontrol agent involved.