Research On Adaptability Under Low Temperature Stress In Osmanthus Fragrans

Osmanthus fragrans is one of the traditional ten kinds of flowers of China, is one of the important landscape greening tree, and it is also the traditional fragrant plant, but in the north of China, due to the limits of low temperature, some difficulties exist in the open air cultivation of O. fragrans, in the present it can not be widely used. Therefore, the research on cold resistant of O. fragrans is of far reaching importance in the introduction and cultivation.This research did cold resistant analysis on O. fragrans form the physiological point, by the way of combination of artifical low temperature and natural low temperature, measured some physiological and biochemical indexes at low temperatures of the O. fragrans, including the relative conductivity, SOD, POD, soluble protein, soluble sugar, proline, malondialdehyde, and relative water content, made comparisons between different cultivars, selected cold tolerant cultivars, preliminarily drew the following conclusions:In the artificial low temperature treatment, by the decreasing of temperature, the relative conductivity of each O. fragrans cultivar showed a trend of increasing, only the temperature when the conductivity abrupt change is slightly different, calculated the semi-lethal temperature (LT₅0) of varieties with the logistic equation, cultivars has lower semi-lethal temperature are O.'Susheng Jingui', O.'Zhusha Dangui', O.'Xiaoye Sijigui'. Besides the low temperature, the drought of early spring is also an important factor affecting the survival.In the artificial low temperature treatment, the SOD showed the trend of"decrease - increase - decrease", when the temperature is higher than -6℃it decreased, then began to rise as the temperature decreased, after the temperature dropped to -24℃, it decreased again. The POD is declining almost from beginning to end, among the cultivars, the POD of O.'Zao Yingui'and O.'Zhusha Dangui'increased slightly near the semi-lethal temperature, and then sharply decreased, while others decreased slowly from beginning to end. by the Analysis of variance, SOD activity was higher in the O.'Zao Yingui'and O.'Qiugui', POD activity was higher in the O.'Jinqiu', O.'Wan Yingui'and O.'Zhusha Dangui'than others.On the analysis of osmotic adjustment substances, under low temperature, the content of proline and soluble protein was decreasing all the time, the soluble sugar content increased slightly at first, and then begin to decline, and greatly increased near the semi-lethal temperature, it may be the result of injury. From the view of both artificial low temperature and low temperature from the natural, poor the osmotic adjustment ability of O. fragrans is poor, showing poor adaptation to low temperature.In the artificial low temperature treatment, decreased at first, later increased, but overall did not change significantly, in the natural low temperature it also showed a trend of decreasing, either seen from the comparisons between cultivars or from the change trend, the MDA content and cold tolerance are not closely related. Under natural low temperature, analysis the adaptability of different cultivars from the relative water content, found that the water-retention capacity are strong in O.'Wan Yingui', O.'Qiugui', O.'Jinqiu'and O.'Xiaoye Sijigui'. After winter, the relative water content of all cultivars have dropped to below 40%, physiological drought caused by low temperature is an important cause of death.Analyze from the relationship between each physiological index and cold resistance, the physiological indexes of O. fragrans are relatively independent, correlation is not obvious, a single index and cold tolerance are not fully consistent, only analyze the index together can we contrast the cold tolerance of varieties. The results of subordinate function and principal component analysis are very consistent with the observed results, are reliable methods to evaluate the cold resistant ability of O. fragrans. Use the method of subordinate function, principal component analysis and cluster analysis on a comprehensive evaluation of 12 Osmanthus fragrans cultivars, inferred the cultivars with good cold resistant are O.'Wan Yingui', O.'Susheng Jingui', O.'Zhusha Dangui', O.'Xiaoye Sijigui', O.'Zao Yingui'and O.'Qiugui', recommended application in the north gardens.