Chitosan as a potential biocontrol agent of plant pathogens and its multiple acting mechanisms: A review

In recent years, chitosan has received extensive attention as a natural biological control agent. We reviewed recent advances and multiple underlying mechanisms, including directly inhibiting plant pathogens (including bacteria, fungi, viruses, nematodes) and inducing plant resistance, of chitosan as a biocontrol agent. Firstly, a total of 23 literatures investigated the direct inhibition of chitosan on plant pathogenic fungi, bacteria and viruses. The positive charge of chitosan interacts with the negative charge groups on the cell surface of pathogenic bacteria, destroying the bacterial cell wall and changing the permeability of cytomembrane. Chitosan can also damage nucleic acids, chelate metal ions for the normal metabolism of pathogenic bacterium, restrain the development of fungal hyphae and spore germination. Secondly, 15 studies focused on chitosan-induced plant resistance. Chitosan acts as a trigger of defensive reactions, enhancing the expression of genes involved in defense mechanisms, increasing the activity of defensive enzymes, activating signal transduction pathways, and promoting secondary metabolites. Thirdly, chitosan can also act on plant tissue culture. In addition, the suppression effect on plant pathogens of chitosan nanoparticles was also discussed. Limitations and future research directions on this issue were proposed. In summary, chitosan has broad application prospects in plant pathogens control.