Antifungal activity of chitosan against Phytophthora infestans, the pathogen of potato late blight

Phytophthora infestans, the pathogen of potato late blight which is a devastating disease of potatoes, causes stem and leaf rot, leading to significant economic losses. Chitosan is a naturally occurring polysaccharide with a broad spectrum of antimicrobial properties. However, the specific mechanism of chitosan on Phytophthora infestans has not been studied. In this study, we found that chitosan significantly inhibited the mycelial growth and spore germination of Phytophthora infestans in vitro, reduced the resistance of Phytophthora infestans to various adverse conditions, and it had synergistic effect with pesticides, making it a potential way to reduce the use of chemical pesticides. In addition, chitosan could induce resistance in potato pieces and leaves to Phytophthora infestans. Transcriptome analysis data showed that chitosan mainly affected cell growth of Phytophthora infestans, and most of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene ontology (GO) terms revolved in metabolic processes, cell membrane structure and function and ribosome biogenesis. Differentially expressed genes (DEGs) related to adverse stress and virulence were also discussed. On the whole, this study provided new ideas for the development of chitosan as an eco-friendly preparation for controlling potato late blight.