| Chitosan (abbreviated as CTS) also known as the deacetylation of chitin, is a high molecular weight cationic polymer. It has many advantages such as natural degradation, non-toxicity, wide variety of sources and so on. Chitosan and its degradation products not only have elicitors activity to induce plant disease resistance, but also can promote plant growth and improve plant stress resistance, which made more and more studies of chitosan come true. But the induction effect of different molecular weight chitosan has obviously difference. Low molecular weight and low polymerization degree chitosan---chitosan oligosaccharides were obtained through oxidative degradation to compare the induced disease resistance difference different polymerization degree chitosan to provide scientific basis for the prevention of the poplar disease.(1) The L9 (34) orthogonal test of chitosan degradation of H2O2, reaction temperature, reaction time and acetic acid concentration four main factors which influence the degradation of chitosan was firstly studied in this paper. Then the effect of each factor on the degree of deacetylation, intrinsic viscosity, molecular weight and color of the degradation products was analyzed. The optimum reaction condition of peroxide degradation of chitosan was screened and low molecular weight and polymerization degree chitosan was obtained. Through the analysis we could get the main factors affecting degradation were the acid concentration and reaction time. The optimum condition by orthogonal test were: 30% H2O210 mL, temperature 60℃, time 6 h, the acetate concentration 2%. Finally, the final product with 87.69% deacetylation degree, intrinsic viscosity 6.28 mL/g, molecular weight of 0.64×104 was obtained. The test showed that the degradation of hydrogen peroxide method was a simple and efficient way of preparation of low molecular weight and polymerization chitosan.(2) The changes of related disease resistance indexs were measured by using different concentrations of chitosan-oligosaccharides and chitosan solution to induce the poplar leaves, indicating two elicitors (inducers) had significant induction effect on poplar disease resistance. The optimum induction concentrations of chitosan-oligosaccharides and chitosan were 10 mg/L and 20 mg/L respectively.(3) Under the optimum concentration , PAL,β-1,3- glucanase,chitinase,lignin content,SOD,CAT and POD which were induced by chitosan- oligosaccharides showed the highest activity which were 3.41,3.89,3.12,2.56,4.01,2.59,2.65 times as high as the each control enzyme activity. The PAL,β-1,3- glucanase,chitinase,lignin content,SOD,CAT and POD activity which were induced by chitosan were 3.15,3.85,3.02,2.56,3.81,2.43,2.59 times as high as the each control enzyme activity. It indicated that the induced effcct of chitosan- oligosaccharides was better than the chitosan. By observing the dynamic changes of resistance indicators we could get that the peak of SOD, CAT and POD was at 8 h after inducing; chitinase was 6 h;β-1,3- glucanase and PAL peaked at 10 h; lignin content got a maximum in 60 h.(4) The resistance of poplar callus induced by elicitors to poplar Dothiorella gregaria was measured by using callus inculation. The result indicated that disease indexes of poplar callus after inducing were significantly lower than control. It showed that disease indexes of poplar callus induced by chitosan-oligosaccharides and chitosan elicitors were lower than control of 37.87%和33.33% respectively in 7 d after inducing. The induced effect of chitosan-oligosaccharides was better than the chitosan.
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