Effects of Volatile Substances from Trichoderma erinaceum M6-5 on the Cell Membrane and Wall of Alternaria alternata, a Postharvest Pathogen of Korla Fragrant Pear

Abstract

In this study, the effects of volatile substances from Trichoderma erinaceum M6-5 on the cell membrane and wall of Alternaria alternata were investigated. To evaluate the antifungal effect, the culture medium inoculated with T. erinaceum and cultured for 5 days was covered with the culture medium containing A. alternata and cultured at 30 ℃ for 3, 5 and 7 days. The mycelia of A. alternata in the treatment and control groups were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and were collected to observe the integrity of the cell membrane by propidiumiodide (PI) staining, and cell membrane-related indexes such as electrical conductivity were measured. The morphological changes of apical growth cells were detected by calcofluor white (CFW) staining, and alkaline phosphatase (AKP) activity and N-acetylglucosamine concentration were determined. The results showed that during the culture period, the volatile substances produced by T. erinaceum had good antifungal effects on A. alternata. SEM and TEM images showed that the mycelia of A. alternata appeared shriveled, swollen and broken partially after the treatment. A greater reduction in cytoplasmic matrix was noted when compared with the control group, which was accompanied by local plasmolysis. For the control group, the mycelium growth was normal, the spore structure was complete, the cross-section structure was clear, the cytoplasm was uniform, and the cell wall and membrane structures were normal. After the treatment, the electrical conductivity, malondialdehyde (MDA) level, protein and nucleic acid leakage significantly increased relative to the control group. PI staining showed that the mycelia of the treated group emitted red fluorescence, indicating that the volatile substances of T. erinaceum damaged the integrity of the cell membrane, thus resulting in the leakage of cellular contents and marked disruption of the normal function of the cell membrane. CFW staining showed no significant differences between the treated and control groups with respect to the fluorescence intensity of mycelia, AKP activity or n-acetylglucosamine concentration indicating that the volatile substances of T. erinaceum did not damage the cell wall of A.alternata, and their major targets were not the cell wall. In conclusion, the antifungal target of volatile substances from T. erinaceum M6-5 is the cell membrane of A. alternata.

Keywords

• trichoderma erinaceum; volatile substances; alternaria alternata; cell membrane; cell wall