Improvement of biocontrol efficacy of Trichoderma harzianum Tr6 vs. Phytophthora drechsleri, the causal agent of damping-off disease in Cucumis sativus

Biocontrol agents have different growth and biocontrol responses under the influence of physicochemical parameters. The culture medium is one of these parameters. Therefore, in this study, the effects of eight liquid media were investigated on the growth and antagonistic efficacy of Trichoderma harzianum Tr6 against Phytophthora drechsleri. Tr6 at 108 spores per ml was grown in these media. All media pH was set at 5.5. Treatments were maintained under a light intensity of 206 Lux and 130 rpm at 28 °C for 10 days. Maximum sporulation (2.5 × 1010 spore/g.dw) occurred in Mol. C. (Sugar beet molasses and Corn steep liquor) medium. The most inhibition against pathogen was related to Mol. M. (Sugar beet molasses and Malt extract) medium. Mol. M. and Mol. B. (Sugar beet molasses and Baker yeast) had the most effect on disease reduction (58.33%). Mol. M. had not superlative effect on plant growth factors but had a better effect compared with other treatments except Mol. Y. (Sugar beet molasses and Yeast extract). The following assays were done to simultaneously select the optimum medium for high sporulation, effective control of disease, and plant growth promotion. Therefore, Mol. M., Mol. B., Mol. C., and Mol. C. B. M. media were used. Mol. C., Mol. C. B. M. and Mol. M. had the highest spore production with 2.35 × 1010, 1.83 × 1010, and 1.65 × 1010 spore/gdw, respectively. There was no significant difference between the Mol. C. B. M. and Mol. M. Furthermore, Mol. C. B. M. reduced disease by 62.5%, but this reduction was not significantly different from Mol. M. and Mol. B. Therefore, Mol. M. medium had the most influence on growth and biocontrol performance of Tr6.