Preliminary Study On Antimicrobial Actiovity And Mechanisms Of Chitosan (Oligochitosan) And Sodium Silicate

Synthetic fungicides are primary methods of controlling postharvest diseases, but with the enhancement of the public's environmental protection and health awareness, research and development of green pesticides becomes a trend of international pesticides in nowadays. Thus natural fungicides are becoming a hot research topic in both home and abroad. Chitosan, which is soluble in dilute acid, is the product of Chitin after deacetylation; and Oligochitosan is a kind of oligomeric with better water-solubility. With good biocompatibility, biological safety and antifungi activity, Chitosan, Oligochitosan and Sodium silicate all have a good prospect, especially in disease contral after fruits and vegetables's grown. But their detailed researches of the mechanisms are insufficient; therefore the author's main work is divided into theree parts as follows:(1) Research on the inhibition of pathogenic fungi and disease control of Sodium silicate on Alternaria citri and Botrytis cinerea. In vitro, the effect on different stages of fungi were not the same: as pH increased, the inhibition of B.cinerea were increased; while the inhibition on mycelium growth of A.citri was relatively strong in the neutral environment, and the germination of spores and germ tube length were inhibited better at higher pH. Sodium silicate had stronger inhibition than nano-silicon and control at the same pH. In vivo, B.cinerea acidify the ambient environments of apple fruit during decay development to reduce tissue pH increased B. cinerea development; but A.citri alkalinize the ambient environments of the wound, local alkalinization reduced decay development. At the same pH, Sodium silicate had better disease control than nano-silicon; nano-silicon almost had no preventive effect. The results therefore suggest that pH played a pivotal role in the inhibitory of si, but si also played a certain role.(2) The antifungi activity of chitosan and oligochitosan against different stages in life cycle of Geotrichum candidum and Alternaria citri was evaluated. With the concentration increased, the inhibitory increased. It also showed that Chitosan and Oligochitosan had difference at different growth period of the fungi. At the spore germination period, G.candidum was more sensitive than A.citri, but at the mycelial growth period, A.citri showed more sensitivity. Also, when at the same growth period, chitosan worked better to inhibite the spore germination of the two fungi while Oligochitosan showed a better performance on depressing their mycelial growth. Chitosan and Oligochitosan both could control the two diseases of citrus fruits to some extent and reduce the fruits'morbidity with a better effect using higher concentration. Oligochitosan had a better control effect on the above diseases than Chitosan did, and they both effected better on G. candidum than A.citri.(3) The antifungi activity of chitosan and oligochitosan against B.cinerea and the preliminary study of its antimicrobial mechanism. Chitosan and oligochitosan inhibited the growth of B.cinerea.at different concentrations, with higer concentration had a better inhibition, and chitosan had a better antifungi activity. B.cinerea served as an example to study the antimicrobial mechanism of chitosan, the results showed that FITC labeled chitosan had stability chemical structure, at low concentration of 001% -0.01% induced fluorescence intensity had a good linear relationship. The success of labeled spore wall and protoplasts preparation laid the foundation for further study of chitosan role sites. H2DCFDA successfully labeled reactive oxidant species (ROS), in order to further explore the influnce of chitosan on the molecular dynamics of cytoplasmic ROS.Therefore, a preliminary study on antimicrobial activity and mechanisms of Chitosan (Oligochitosan) and Sodium silicate was made, which laid a foundation for the better anti-decey of fruits and vegetables and research on green pesticide.