Study on the antifungal mechanism of Chinese herbal extract on Botryosphaeria dothidea

Botryosphaeria dothidea is a main post-harvest pathogen of kiwifruit, causing fruit decay and health problems. In this study, the effect of Chinese herbal extract compound (CHEC) on the antifungal assay, the SEM (scanning electron microscope) observation, fluorescence microscopy observation, transcriptional profile, and physiological characters of B. dothidea was measured. CHEC (0.6 to 0.8 mg/ml) significantly inhibited mycelium growth, reduced the formation and germination of spores, and decreased the content of sugar and protein in the mycelium. The activity of SOD, CAT, POD, NADP-malate dehydrogenase, succinate dehydrogenase, cellulase, and glucanase was significantly reduced, while the content of malondialdehyde in the mycelium was significantly increased. In addition, there was a significant decrease in DNA content and mitochondrial membrane potential and a significant increase in ROS. The mycelium appeared thicker, the top of the mycelium was significantly larger, the cell membrane of spores began to contract and bend, and the nucleus gradually disappeared. Transcriptome data showed that a total of 20,510 differentially expressed genes (DEGs) were obtained, including 19,139 down-regulated and 1371 up-regulated genes. Both RNA-seq data and qRT-PCR showed that the genes of remarkable down-regulation were included in the membrane pathway, cell pathway, oxidoreductase activity pathway, transport and catabolism, and carbohydrate metabolism. Practical applications CHEC is a mixture of several extracts with strong antifungal effects. It is a green and safe antifungal agent. CHEC has a strong antifungal effect by destroying mycelial cell structure, inhibiting gene expression and mycelial growth and metabolism. These findings provided additional useful information on the antifungal mechanism of CHEC at the molecular and genetic levels, and suggested that CHEC was a potential candidate to control B. dothidea. Moreover, our data provided novel insights into the green and safe preservation of kiwifruit.