Biocontrol Potential and Growth-Promoting Effects of Freshwater Trichoderma Strains against Plant Pathogenic Fungi in Red Pepper

The aim of this study was to investigate the biocontrol potential of Trichoderma spp. against plant pathogenic fungi. Forty-four Trichoderma strains isolated from freshwater environments were evaluated for their biocontrol potential against Phytophthora capsici and Fusarium solani, as well as for their siderophore production, phosphate solubilization, and enzymatic activities. Seven Trichoderma strains showed excellent performance and were selected for further experiments. These strains were identified as T. longibrachiatum and T. capillare based on the internal transcribed spacer and translational elongation factor 1-alpha gene sequences. The selected strains demonstrated strong antifungal activity against six fungal pathogens in dual-culture and volatile organic compound (VOC) assays. Strain FBCC-F1645 exhibited particularly high antifungal activity and completely inhibited the growth of P. capsici in the VOC assay. All the selected strains significantly enhanced the growth parameters of red pepper seedlings, and flowering was effectively promoted in the treatment groups. Additionally, these strains demonstrated preventive effects against Fusarium oxysporum and P. capsici, the causative agents of Fusarium wilt and Phytophthora blight, respectively, achieving notable control efficacy. Notably, strain FBCC-F1547 completely inhibited wilting and exhibited a strong preventive effect against blight. In the pepper anthracnose prevention experiment, all the tested strain suspensions (diluted 100-fold and 500-fold) effectively inhibited Colletotrichum acutatum. These findings suggest that Trichoderma spp. isolated from freshwater environments have the potential to reduce chemical pesticide use and promote sustainable agriculture.