| 1. The effects of three kinds of chitosan on radial growth seventeen phytopathogenic fungi was investigated in vitro. Except 2 fungi, the radial growth of 15 fungi tested was inhibited by three kinds of chitosan. The inhibit effect to fungi of water-soluble chitosan C-3 was the most effective, and it's antifungal activity was increased when it's concentration increased. The antifungal activity of chitosan C-l and chitosan C-2 had no significant difference, but the most effective concentration was related to the kind of phytopathogenic fungi. The main antifungal mechanism of different molecular weight chitosan was different.2. Chitosan was effective in inhibiting radial growth and sporogensis of F. oxysporum. f. sp. lycopersici and Alternaria solani(E. et M.) Jans et Grout in vitro. The inhibiting activity of chitosan was increased when its concentration increased. Light microscope observations showed that chitosan at concentration greater than Img/ml induced morphological changes, including hyphal swelling, distortion, excessive branching, shortening of hyphal segments in new hyphal of F. oxysporum. f. sp. Lycopersii and Alternaria solani(E. et M.) Jans et Grout. The resistance mechanism of chitosan is related to its ability to increase the permeability of the fungal plasma membrane.3. It's no significant relationship between seedling weight, stem diameter, chlorophyll content, FW of top, DW of top, FW of root and P content in tomatoes with spraying different concentrations of chitosan. It could make tomato's DW of root, root/top, and N, K content of top and root to increase significantly. Img/ml chitosan can adjust the ratio of N: P: K in top of tomato. The plant's response to stress will increase with the increased root/ top. The increasing K content in plant has the relationship to resistance to disease.4. It could make the tomato plants resistance to early blight when the tomato seedlings were induced by chitosan (Img/ml) at the stage of the forth leaf. Chitosan treatment of tomato leaves before inoculation reduced the rates of diseased leaf and disease index, the rates of diseased leaf of resistant and susceptible tomato cultivars were 35.9% > 34.2%$I 34.9% respectively and lower than inoculation control significantly. The relative immunization efficiencies of the three tomato cultivars were 39.8%, 49.9%fll 56.4%, respectively. Chitosan-treated leaves induced an increase in POD, PPO, PAL, chitinase, (3-1,3- glucanase activities. The activity of these enzymes induced by chitosan in difference tomato cultivars showed different. Different enzymes vary differently after chitosan.5. Both of activities of POD and PPO in the tomato inoculated with Alternaria solani(E. et M.) Jam et Grout arc higher than those treated with chitosan. However, chitosan can induce the activities of PAL, chitinase andfi-1,3- glucanase more strongly. At early stage of treatment, these activities in tomato treated with chitosan are higher than those in plants inoculated with Alternaria solani(E. et M.) Jans et Grout. It shows that the inducation of POD and PPO by chitosan is the plant's response to stress, hut that chitosan can induce of PAL, chitinase and p-1 ,3- glucanase specially.6. Enzyme activity staining showed that no new isoforms of peroxidase were found in the leaves of plants treated with chitosan or inoculated with Alternaria so!ani(E. et M.) Jans et Grout. But the densities of bands are relevance with the results of enzyme activities. Our data indicates that early blight and chitosan do not induce new isoforms of POD, but improve the level of POD protein.7. We designed the PCR primer according to the homology sequence of P~l,3- glucanase induced by fungi and amplified a cDNA fragment by RT-PCR. The blast result showed that it was a gene P-1,3- glucanase of tomato. Chitosan can induce the expression of this gene strongly. In an hour of treatment of chitosan, the expression of P-1,3- glucanase was improved by sever...
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