Study And Identification Of Colletotrichum Gloeosporioides Penz From Guangxi Province And Coating Preservation On Litchi Under Normal Temperature

Litchi, as a kind of famous fruit in the subtropical zone, is well-known ail over the world for its special color and delicious flavor; however, it is very difficult to preserve this fruit under normal temperature. In this thesis, preservation of litchi was studied under normal temperature by coating, based on the damage which result in browning of litchi pericarp, induced by pathogen, and the usages of new-type material, such as nano-ZnO, etc.A pathogenic fungus, was isolated from the damaged fruit of feizixiao and purified; moreover, a 576 bp rDNA (partial) ITS fragment which was obtained by PCR from total DNA of it with a internal transcribed spacer (ITS) universal primers, was cloned into E.coli (JM109). When BLAST search for comparisons of the sequences was used after sequencing, it is very closed to Colletotrichum gloeosporioides from Germany with 99.31% identity. At the same time, the fungus has been characterized biologically, the result was shown that the optimum temperature and pH for its growth was 25-30℃ and 5.5-8.5, in addition, the fungus can grow but with a little difference in biological aspect on many kinds of media. However, it grew faster on the vegetable-component medium such as PDA than it did on the others.In all the fungicides, Sportak was the most effective suppressor, dehydroacetic acid canalso suppress the fungus, and so did garlic extract.From the study on refined konyaku starch modification, a new-type coating agents, it could be seen that both sorbic acid and citric acid were the best of all modificative agents in the experimentation because they could enhance the expansivity and the abrasion resistance of konjaku gluccomannan (KGM, 80% of refined konjaku starch). Using KGM modified and other coating agents as major dispersants, and homogenizing the composite hyper-dispersants including nano-ZnO (2%) by High-Pressure-Homogenizer, the effect of dispersedness was very good and much better than that of by ultrasonic traditionally.When litchi were dipped in coating agents solution and packed in thin plastic bags, the rate of its weight lost was down, while the efficiency of its browning resistance was up. From the experiments with each one of agents individually and compositely, it was illustrated that nano-material was useless when being added into alone but it played a positive role with stronger fungicides such as Sportak together; and that Sportak, dehydroacetic acid and kojic acid, acted a same key roles in keeping-fresh, nevertheless, citric acid always play a negative role .