Researches On Cold Resistance Of 3 Salix Zhuliu Strain

As a superior timber and ornamental strain, Salix Zhuliu results from the hybridization of Salix Zanliu, Salix koreensis Anderss and Salix linearistipularis, has the characteristics of high ornamental value and fast growth and is mainly used in planting in saline alkali land, building in forest areas and constructing fast-growing economic forests. Currently, however, there are few studies of the cold resistance of Salix Zhuliu. The cold resistance of three strains of Salix Zhuliu is evaluated to provide bases for the introduction of strains of Salix Zhuliu in cold regions. Three strains of Salix Zhuliu (Nos.3,5 and 7) selected as experimental material and weeping willow as reference, this paper compared the cold resistance of the three Salix Zhuliu strains and weeping willow by analyzing the psychological indexes of their cold resistance (which are obtained by means of natural and artificially simulated low-temperature treatment) and their natural winter growth performance. In the experiment both the natural condition and the gradients of artificially simulated low temperatures were set; the relative conductivity of the branches of the selected materials was determined and their psychological indexes of cold resistance were determined in the aspects of the soluble protein content, SOD, POD, free proline content and MDA content, too; the effective temperature range was determined; LT50 was obtained with the Logistic equation; such methods as Principal Components Analysis and Membership Function Calculation, combined with the winter growth performance of the Salix Zhuliu strains and the weeping willow, were also applied in evaluating the cold resistance of Salix Zhuliu and weeping willow comprehensively. Results were as follows: Firstly, the LT50 of Salix Zhuliu No.3,5 and 7 and weeping willow was-31.13℃,-35.16℃,-32.39℃ and-28.18℃ respectively.Secondly, analyzing the cold resistance indexe of each Salix Zhuliu strain and weeping willow and comparing the maximum and average values of their cold resistance indexes revealed that the cold resistance of each Salix Zhuliu strain was stronger than that of weeping willow in natural low temperatures. An analysis based on the Membership Function method showed the cold resistance of each Salix Zhuliu strain and weeping willow was sorted as Salix Zhuliu No.5> No.7> No.3> weeping willow. Thirdly, the analysis of the cold resistance index of each Salix Zhuliu strain and weeping willow and the comparison of the maximum and average values of their cold resistance indexes drew the conclusion that the cold resistance of each Salix Zhuliu strain was stronger that of weeping willow in artificially simulated low temperatures. An analysis based on the Membership Function method indicated the cold resistance of each Salix Zhuliu strain and weeping willow was sorted as Salix Zhuliu No.5> No.7> No.3> weeping willow. Fourthly, the field observation of the winter survival rate of the Salix Zhuliu strains and weeping willow and the degree of their winter injury showed that the cold resistance of each Salix Zhuliu strain and weeping willow was sorted as Salix Zhuliu No.5> No.7> No.3> weeping willow, which agreed with Results No.2 and 3 completely.