The Antimicrobial Activity And Effect Of Disease Control Of Chitosan Or Oligochitosan On Postharvest Fruits

Pathogens– infection is one of the important reasons of the loss of fruit and vegetable during postharvest storage and transportation. Synthetic fungicides are primary methods of controlling postharvest diseases, but concerns about public health and environment are limiting the use of synthetic fungicides, even some synthetic fungicides are prohibited in some developed countries. Thus, natural fungicides are becoming a hot research topic. Chitosan not only has antifungi activity but also can induce defence reactions of plant; thereby it has a bright future. Detailed researches are insufficient, so following work were carried on.â‘´The antifungi activity of chitosan and oligochitosan against different stages in life cycle (spore germination, germ tube elongation and rmycelial growth) of several phytopathogenic fungi was evaluated.Chitosan and oligochitosan inhibited spore germination, germ tube elongation and mycelial growth of the fungi with an effect of concentrations, and the results suggested the effect of chitosan and oligochitosan on different stages of fungi were not same. The hypha was more sensitive than the spore. Thus fungi under different stages of life cycle had different resistance against chitosan or oligochitosan, and different strains also have different resistance. Moreover, results had also indicated that combination of oligochitosan and silicon had better antifungi activity, especially for the growth of hypha.⑵M. fructicola served as an example to study the antimicrobial mechanism of chitosan and oligochitosan was evaluated.The spore was stained with propidium iodide (PI), and the result showed that the plasma membranes were damaged. From the result of dyeing by lactophenol-cotton blue, it could be concluded that the cytoplasm content of hypha treated by chitosan or oligochitosan might leak, which might be caused by the damage of plasma membranes. The result also showed the structural altered in M. fructicola in response to chitosan. ⑶The effect of chitosan or oligochitosan in reducing storage decay of some fruit was studied.Chitosan and oilgochitosan could control the several postharvest diseases of brown rot of peach, pear black spot, pear ring rot and blue mould of citrus. Treatments could reduce disease incidence of fruits, and obviously the higher concentrations had better effect. Synergistic effect of oligochitosan and silicon was better than oligochitosan in controlling brown rot of apple.â‘·Intensification of defense mechanisms by chitosan and oilgochitosan was evaluated.The enzymatic activities of PPO, POD, GLU and CHI were evaluated after the pear fruits were treated by chitosan and oligochitosan with concentration of 0.15%. Treatments can improve the the enzyme activities of GLU and CHI.Physiological responses about defense response were evaluated and the expressions of POD and GLU genes were analyzed after the peaches were dipped into the solution of chitosan and oligochitosan. The results suggested that chitosan and oligochitosan with different concentrations could improve the enzymatic activities of POD, GLU and CHI and affected the content of H₂O₂ and the activity of CAT. Result of northern-blotting showed that chitosan and oligochitosan with concentration of 0.5% stimulated the expressions of POD and GLU genes.