Abstract: 【Objective】Breeding of resistant poplar strains is a fundamental method for controlling Osier weevil (Cryptorrhynchus lapathi). But until now, the researches related to the mechanisms of poplar resist to Osier weevil and the breeding of resistant poplar strains are seldom. To establish a basis for breeding new poplar strains resisting to Osier weevil, a study was carried out to find out the relationship between the resistance level of poplar strains to Osier weevil and the physical properties of their trunks.【Method】The population density of Osier weevil on different poplar strains, percentage of infested poplar strains, as well as the hardness of xylem and phloem, thickness of phloem, diameter at breast height (DBH), the parental origins of 67 different 2- to 3-years-old poplar strains were studied.【Result】1) The strains were immune to Osier weevil when the xylem hardness was over (45.43±3.59) HD, and those strains were highly resistant when the xylem hardness reached to (44.17±2.76) HD. The average xylem hardness of resistant, susceptible and highly susceptible strains was (43.6±0.53) HD, (40.39±2.98) HD and (39.47±2.98) HD, respectively. If the phloem hardness of a poplar strains is over (33.96±4.72) HD, it might be a very higher resistant strains. The strains were immune to Osier weevil when the phloem hardness was over (32.61±2.69) HD. The average phloem hardness of resistant, susceptible and highly susceptible strains was (31.13±0.72) HD, (28.08±3.98) HD and (24.75±3.19) HD, respectively. 2) The strains were immune to Osier weevil when the DBH was (33.38±6.08) mm, and those strains were highly resistant when the DBH was (36.65±3) mm. The average DBH of resistant, susceptible and highly susceptible strains were (41.31±1.56) mm, (43.34±6.8) mm, and (48.16±2.52) mm, respectively.3) Comprehensive analysis on relationship between parental origins and poplar resistance level by a regressive analysis, Most of the P. deltoides×P. pseudo-simonii, P. deltoides × P. cathayana and P. deltoides×P. suaveolens strains were resistance to C. lapathi. Most of the P. nigra×P. deltoides, P. deltoides, P. deltoides×P. maximowiczii and P. nigra× P. simonii strains were susceptible. 【Conclusion】The harder the phloem and xylem of poplar strains was, the higher their resistance level to Osier weevil was. By the contrast, the softer the phloem and xylem were, the lower their pest resistance level was. Among those studied strains, when the radial growth of poplar strains was faster, then its DBH would be larger and its resistance ability was lower. Strains from different parental origins showed different pest resistance ability. P. pseudo-simonii, P. cathayana and P. suaveolens strains of Section Tacamahaca were resistant to Osier weevil. P. nigra and P. deltoides of Section Aigeiros strains were susceptible. In the breeding of highly resistant strains to Osier weevil, P. pseudo-simonii, P. cathayana or P. suaveolens could be chosen as parents, and P. deltoides or P. nigra should not be chosen as parents.

Key words: poplar, xylem hardness, phloem hardness, diameter at breast height (DBH), biological parent, resistance