Due to the high environmental risk of chemical pesticides, biological control of plant diseases with bio-pesticides are highly encouraged
and recommend. Chitosan and oligochitosan are the well-known biological control agent for its nontoxic, biodegradable and
biocompatible properties. Chitosan is considered as the most abundant natural polymer with a dual effect: It controls pathogenic
microorganisms by preventing growth, sporulation, spore viability, germination and disrupting cell and inducement of different defense
responses in host plant inducing and/or inhibiting different biochemical activities during the plant-pathogen interaction. Chitosan has
been assayed for control numerous pre and post-harvest diseases of many crops. Chitosan also has the positive effect of enriching
biodiversity in the rhizosphere. Meteorological effect on chitosan is little evaluated. For achieving the goal of sustainable agriculture,
chitosan will become a popular plant protectant.