| Melampsora larici-populina Kleb. also known as Populus cathayana rehd puccinia triticina,a heteroecious fungi which is widespread and destructive,could invade cathay poplar group,black poplar and more than 20 kinds of hybrid poplar, and is all over the word of poplar cultivation area. It is distributed mainly in northeast, northwest, southwest and north china, which caused serious damage.In this paper, Populus deltoides×P. nigra seedlings and detached leaves have been taken as the materials, besides Salicylic acid and Chitosan oligosaccharides as the inducers, in two separate induction and their cross-processed to determine correlative resistance physiological index and pathogen inoculation, the possible physiological mechanism of disease resistance and role of Salicylic acid in the induced systemic acquired have been studied. The results are as follows:1. Using chitosan as raw material, to prepare Chitosan oligosaccharides by adopting the method of H2O2 oxidative degradation, the molecular weight of Chitosan oligosaccharides in this method was between 1000 and 2000, average value was 1.82×104, which was lower two orders of magnitude than chitosan'average molecular weight (1×106-2×106)2. Salicylic acid and chitosan oligosaccharides could induce a significant increase in PAL, Lignin,β-1,3-glucanase,Chitinase and HRGP, The induction effect was related to inducer concentration and induction time. The induction effect of elicitor was increased with the elevation of the concentration In a certain concentration range, when the concentration of Chitosan oligosaccharides was 10mg/L and of Salicylic acid was 100mg/L the effect was optimum, then not increasing or decreasing above this concentration. All the results have exhibited that the inducer (elicitor) had basic characteristics,which proved that Salicylic acid and Chitosan oligosaccharides were effective inducer, plant disease resistance was obviously increased through induction treatment.3. According to induction time process, correlative resistance physiological index showed obviously ebb and flow process. Induction of two indicators to different resistance index in induced lag and the peak period was some differences.The peak value of PAL activity emerged as early as 36 hours or so, and ofβ-1,3-glucanase and Chitinase appeared in 48 hours, while the peak value of HRGP did not appear until 60 hours, Lignin maximum content occurs later than 72 hours. It showed that, induction had expressed relative enzymes'gene, which could firstly synthetise phenolics and phytoalexin secondly the resistance hydrolase,finally the HRGP and Lignin.4. The induction effect of cross-processed of SA and COS to relative resistance index was apparently higher than their individual induction.Proved that there was a certain internal relation between SA and COS in eliciting resistance of plant. Generally recognized that elicitor induced resistance of plant, especially systemic acquired resistance by inducible producing SA,then inducing resistant response as SA a signal molecule.According to the induction effect of cross-processed(had definite synergized action),both were not a simple linear relationship,maybe a certain internal relationship,this will be proved by further study.5. Treating with SA and COS some time later, pathogen(Melampsora larici-populina Kleb.)inoculation experiment of poplar detached leaves proved that, the latent period was significantly delayed compared with contrast test, The sporulation of leaf disc which treated with chitosan oligosaccharides reduced by 30% compared with the control, treated with Salicylic Acid reduced by 50%.6. Local treating poplar seedlings(one Leaf) by SA, may cause resistance physiological index of other untreated leaves of the whole plant increased or enhanced. Meanwhile pathogen inoculation experiment Showed, local treatment could induce poplar seedlings' resistance to Melampsora larici-populina Kleb, pathogen inoculation experiment proved that porulation of untreated lesves notably reduced, the result showed that SA played a key role in systemic acquired resistance,was an important elicitor in SAR.
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