| Larch is main specie of forest in northeast area of China, which often attracked by Dendrolimus superans and has serious harmful result. Currently in order to plant healthy trees to reduce the erosion of pests, researchers not only to find effective forest management measures, but also need to study the essence of the inner of interaction on relationship between insect and plant. Therefore, high resistant trees were more and more attention to resist pests. In this research, the F1 generation and F2 generation after Larix kaempferi, L. gmelinii and L. olgensis hybrided were selected as objects of for research. Contents of secondary plant metabolites and the activities of antioxidative enzymes, defensive enzymes and proteinase inhibitor in healthy needles were detected. The differences of constitutive resistance between different varieties were analysised, which proviced more evidence to alleviate pests of larch and improve the abilities of resistance of trees. After research, results were listed below.(1) The influences of strain to the contents of tannin and phenolie acids in needles of larchTannin contents were tested by the method of the vanillin colorimetry. The sesult showed that there was difference between different strains from the same generation and there was difference between different generations from the same strain. The tannin contents were the same tendency at June and July, and the contents of June were higher than July in two generation.Phenolie acids were tested by HPLC. It suggested that there were 10 phenolie acids in needles of 7 strains of two generations, which were benzoic acid, caffeic acid, chlorogenic acid, cinnamic acid, phenylacetic acid, ferulic acid,p-coumaric acid, salicylic acid, syringic acid and vanillic acid.10 phenolie acids had difference between each other, which showed larch resistance had difference between different strains/filial generation. Contents of ferulic acid and vanillic acid of F2 generation were higher than F1 generation; other phenolie acids of F1 generation were higher than F2 generation. It more proved that heterosis of F1 generation was higher than F2 generation. Benzoic acid and phenylacetic acid between 7 strains of F1 generation, phenylacetic acid and syringic acid of F2 generation had difference, therefore speculated that phenylacetic acid, benzoic acid and syringic acid had stronger resistant effort for healthy growth of larch.(2) The influences of strain and growth period to the activities of protective enzymes in needles of larchPerexidase (POD), eatalase (CAT) and superoxide dismutase (SOD) were important enzymes of protective enzymes. The POD, CAT and SOD activities were assayed with UV-spectrometry. It showed 3 enzymes activities of F1 or F2 generation at June were higher than at July (P>0.05). CAT activity and SOD activity of F1 generation were higher than F2 generation, which suggested heterosis of F1 generation was higher than F2 generation. The best resistant combination of 7 strains was L. kaempferi and L. gmelinii.(3) The influences of strain to the activities of defensive enzymes in needles of larchPhenylalanin ammonialyase (PAL) and polyphenol oxidase (PPO) were defensive enzymes that contribute to the defensive responses in plants. It showed that the activities of PAL and PPO of L. kaempferi 12×L. gmelinii 9, L. kaempferi 3×L. gmelinii 9 and L. kaempferi 5×L. olgensis 78-3 were higher. The activity of PAL in more strains of F1 generation was higher than F2 generation. The activity of PPO of F1 generation was higher than F2 generation at July, but lower than F2 generation at June. It suggested that heterosis of F1 generation was higher than F2 generation, but F2 generation also had heterosis and F2 generation could to be used.(4) The influences of strain and growth period to the activities of proteinase inhibitor in needles of larchTrypsin inhibitors (TI) and Chymotrypsin inhibitors (CI) are the substances, which can inhibit the growth of insects. The research showed that the activities of TI and CI of L. kaempferi 5×L. gmelinii 9, L. kaempferi 3×L. gmelinii 2 and L. kaempferi 5×L. olgensis 78-3 of two generations were higher. The the activities of TI and CI of F1 generation were higher than F2 generation (P<0.05), and in more strains of two generations were higher at July than at June.(5) The cluster analysis of strain of F1 generation and F2 generationIn the research,L. kaempferi 3×L. gmelinii 2, L. gmelinii 7×L. kaempferi 77-2 of F1 generation and L. kaempferi 3 x L. gmelinii 9 of two generations were one cluster; L. kaempferi 12 x L. gmelinii 9, L. kaempferi 5×L. gmelinii 9, L. gmelinii 7×L. kaempferi 77-2 and L. kaempferi 5×L. olgensis 78-3 of F2 generation were one cluster; other 6 strains were one cluster. The differences of constitutive resistance between different varieties were studied, which proviced prerequisite and foundation for growing healthy trees. Therefore, to use better larchs such as L. kaempferi 3×L. gmelinii 2 of F1 generation, L. kaempferi 3×L. gmelinii 9 of two generations had important significance for improve resistent ability of trees and reduce the damage.The resistance mechanism of tree is a complex system. The strain and growth period had impact on resistance of larch. There was different heterosis between the same or different strains of Hybrid larch after choosing. Therefore, choose better larchs such as L. kaempferi 3×L. gmelinii 2 of F1 generation, L. kaempferi 3×L. gmelinii 9 of two generations for growing was an effective way.
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