Biocontrol Mechanisms of Trichoderma koningiopsis PSU3-2 against Postharvest Anthracnose of Chili Pepper

Abstract

Several mechanisms are involved in the biological control of plant pathogens by the soil-borne <i>Trichoderma</i> spp. fungi. The aim of this study was to characterize a new strain of <i>Trichoderma</i> as a potential biological control agent to control the postharvest anthracnose of chili pepper caused by <i>Colletotrichum</i><i>gloeosporioides</i>. A total of nine strains of <i>Trichoderma</i> spp. were screened for their antifungal activity using a dual culture assay against <i>C.</i><i>gloeosporioides</i>. <i>Trichoderma koningiopsis</i> PSU3-2 was shown to be the most effective strain, with a percentage inhibition of 79.57%, which was significantly higher than that of other strains (<i>p</i> < 0.05). In the sealed plate method, <i>T. koningiopsis</i> PSU3-2 suppressed the growth of <i>C.</i><i>gloeosporioides</i> by 38.33%. Solid-phase microextraction (SPME) was applied to trap volatiles emitted by <i>T. koningiopsis</i> PSU3-2, and the GC/MS profiling revealed the presence of antifungal compounds including azetidine, 2-phenylethanol, and ethyl hexadecanoate. The production of cell-wall-degrading enzymes (CWDEs) was assayed through cell-free culture filtrate (CF) of PSU3-2, and the enzyme activity of chitinase and <i>β</i>-1,3-glucanase was 0.06 and 0.23 U/mL, respectively, significantly higher than that in the control (<i>p</i> < 0.05). Scanning electron microscopy of the mycelium incubated in cell-free CF of <i>T. koningiopsis</i> PSU3-2 showed the abnormal shape of <i>C.</i><i>gloeosporioides</i> hyphae. Application of <i>T. koningiopsis</i> PSU3-2 by the dipping method significantly reduced the lesion size (<i>p</i> < 0.05) after inoculation with <i>C.</i><i>gloeosporioides</i> compared to the control, and there was no disease symptom development in <i>T. koningiopsis</i> PSU3-2-treated chili pepper. This study demonstrates that <i>T</i><i>. koningiopsis</i> PSU3-2 is an effective antagonistic microorganism and a promising biocontrol agent against postharvest anthracnose of chili pepper, acting with multiple mechanisms.