| The chitosan is the second biggest organic matter in the nature. It not only has far-ranging anti-virus capability, but also can induce various plants to generate anti-disease ability. The wilted bitter gourd is one kind of soil-borne pathogen diseases caused by Fusarium oxysporum. Its rate of incidence is very high. So it is a very important disease that harms the bitter gourd.Firstly,310 isolates of Fusarium species were obtained from 280 bitter gourd plants with wilt symptom in the Jinhua plots in Zhejiang province. Based on the culture characteristics, morphological characteristics and molecular biology characteristics, these pathogens of bitter gourd wilt were identified as Fusarium oxysporum. Then through pathogenicity and forma specialis identification test, the results showed that Fusarium. oxysporum proved to be obvious pathogenic to the bitter gourd and less or no pathogenic to other tested plant species. So it was proved that these wilted bitter gourds were caused by Fusarium oxysporum. f. sp. momodicae. We called this strain F.ox.m in the following.Secondly, based on the laboratory predecessor's studies, the antifungal activities and so on of chitosans with different concentrations to five kinds of pathogens were investigated in vitro. It was found that the chitosan had a certain extent influence on the colonial morphology and structure, hypha shape, propagate and so on of the treated pathogens. And the antifungal activities increased as the chitosan concentrations varied from 0.25 g/L to 5.00 g/L. The higher concentration of chitosan was, the more remarkable influence of its antifungal activity was; but there was not a linear correlation; when concentration of chitosan was 0.25 g/L, the growth of three pathogens(Fusarium graminearum,Fusarium oxysporum. f.sp.cucumerinum,Fusarium oxysporum f.Sp.momdicae) were restrained except Rhizoctionia solani and Pythium ultimum. (P< 0.05), which indicated that the effect of chitosan to the Fusarium is more obvious. In addition, the effect of chitosan to Fusarium oxysporum f.sp.momdicae was the most obvious in the 3 Fusariums.Thirdly, the antifungal activity of chitosans with different molecule weights (MWs) and concentrations against F.ox.m were investigated in vitro, and the antifungal mechanisms were analyzed at the same time. As a result, the aberrance of hypha shape and structure, growth condition and metabolism were found. Except for the one of 5.OX 103, the antifungal effect of chitosans with higher MW increased with MWs increasing; With the same MW, the antifungal effect increased with concentrations increasing. The soluble proteins of F.ox.m were greatly changed on the activity of chitosans.Fourthly, the bitter gourd were inoculated F.ox.m in the seedling stage by the way of soaking roots and needle break, and the antifungal activities of seven bitter gourd varieties were tested. The results showed that Xing-Shu-Chun-Yan, Da-Bai, Cui-Lv-Nen-Yu, and Lv-Xian-Feng-Za-Jiao were susceptible with F.ox.m. And Chang-Bai, Jing-Xuan-Chang-Lv and Qing-pi had middle resistance. At last, no high resistance varieties were found. Taking susceptible varieties (Xing-Shu-Chun-Yan and Lv-Xian-Feng-Za-Jiao). and middle.resistance varieties(Chang-Bai, Jing-Xuan-Chang-Lv) for the investigation of a Specific molecular weight chitosan's anti-inductivity to F.ox.m., the results showed that the resistances of each bitter gourd variety to F.ox.m. all improved to some extent under the influence of chitosans. But the resistance of Lv-Xian-Feng-Za-Jiao and Xing-Shu-Chun-Yan had increased more significantly, and the resistance of Chang-Bai and Jing-Xuan-Chang-Lv had increased less significantly.Finally, the phenylalanine ammonialyase (phenylalanine ammonialyase, PAL) and the peroxidase (peroxidase, POD) were two important enzymes related to the plant disease-resistant response. The changes of POD and PAL activities in the bitter gourd were studied after inoculated with chitosans of different molecular weights. The result indicated that the activities of POD and PAL enhanced in varying degrees after the treatment of different chitosan solutions. So these two enzymes may possibly participate in the balsam pear's anti-wilt response. But, the change characteristics of these two enzyme activites were not identical. The reason possibly was that they played different roles in the balsam pear's disease-resistant system. In addition, chitosan's molecular weight obviously effected balsam pear's anti-inductivity. |
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