Studies On Genetic Diversity Of Zenia Insignis Provenances And Their Resistance To Low Temperature Stress

Zenia insignis, one of the most valuable, rare, rapid growing species with multi-functions, has a bright prospect of utilization. As pioneer tree species in difficult forestation regions, the wild resources of Z. insignis were getting extinct. Z. insignis has been introduced to Fujian, Jiangxi and Zhejiang provinces, and its capability of rapid growing excelled indigenous trees and equaled to poplar and eucalyptus. Previous researches on Z. insignis focus on cultivation techniques, while no other basic researches were reported. This paper investigated genetic diversities of Z. insignis provenances and their resistance to low temperature stress using nine Z. insignis provenances collected from their main distribution areas as materials from 2005 to 2007. Moreover, genetic diversity of the Z. insignis provenances was estimated by combination of ISSR marker and provenance experiments in seedling stage. This study would provide a scientific base for cultivation and breeding of Z. insignis. The main results are as follows:1. The growth pattern in seedling stage of different Z. insignis provenances. Experiments were involved in nine provenances including Tongdao and Jianghua in Hunan, Yingde and Wongyuan in Guangdong, Guilin, Pingguo, Xincheng and Jingxi in Guangxi, and Xingyi in Guizhou. Results showed that there were extremely significant differences in seed sizes and leaf sizes between different provenances which were considered to be important characters distinguishing different provenances. Extremely significant differences were not present in production volume in different seedling stages, but in capability of cold resistance which was indicated by field experiments. Provenance of Tongdao, Hunan, could safely winter under the conditions of daily lowest temperature below 0℃, even by -6.1℃within durative seven days, showing good capability of resistance to stress. Therefore, special characters such as cold resistance should be considered as indexes when performing Z. insignis provenance selection. Individual selection played a key role in selection and breeding of superior and rapid growing varieties of Z. insignis. Growth pattern in seedling stage of different Z insignis provenances was investigated. The growth model was established by Logistic equation. From this equation it could be found that small seedlings began to accelerate growth from June after transplanting, and then rapidly grew from July to August. The peak stage of stem diameter growth was earlier than that of height growth, suggesting that Z. insignis is drought resistant. 2. The cold resistance of different Z. insignis provenances. Results showed that physiological substances in Z. insignis seedlings changed after low temperature treatment. For instance, contents of protective substances such as soluble proteins and soluble carbohydrates, and osmotic adjustment substances such as free praline increased, and activities of antioxidative Enzymes were also increased. At 7℃the contents of soluble proteins, soluble carbohydrates and praline, and the activities of SOD and POD reached by the maximum values, whereas the content of MDA by the minimum value when the strongest cold resistance was developed. After treatment with low temperature, physiological indexes in Z. insignis shoots varied and showed significant differences at certain value of low temperature. There was a big increase in the contents of soluble proteins after being treated with -8℃, and the contents of MDA increased a little. The SOD activities between different Z. insignis provenances began to show significant differences. Relative electric conductivity sharply increased after treatment with -12℃, and that of all provenances apart from Tongdao provenance reached over 50%. The membrane of cytoplasms was damaged. Leaf anatomical analysis indicated that cell tense ratio (CTR) and spongy ratio (SR) of Z. insignis leaf were correlated with its cold resistance; the cold resistance ability became stronger with the increase of CTR and the decrease of SR. According to the Logistic equation, it could be calculated the semi-lethal temperature of Tongdao provenance was -13.06℃which is 0.89℃～2.74℃lower than that of the other provenances. The crystallization temperature of leaf of Tongdao provenance was -15.04℃indicated by DSC which is 0.42℃～1.34℃lower than that of the other provenances. Integrated analyses showed that the cold resistance of Tongdao provenance planting stock was the strongest, followed by Xinyi, Xincheng, Yingde, jianghua and Jingxi provenances.3. The genetic diversity of different Z. insignis provenances. ISSR-PCR reaction system for genetic diversity analysis of Z. insignis was successfully established for the first time. Averagely, each of the 10 primers screened amplified 5.4 bands, and the mean Percentage of Polymorphic Bands (PPB) was 64.29%. Among the six provenances, the mean PPB was 56.48%, Shannon's Information index 0.3048, Nei's index 0.2052, suggesting certain degree of genetic divergence exists among provenances. The genetic diversity of Xincheng provenance was the highest followed by Jianghua, Yingde, Jingxi, Tongdao and Xingyi provenances. Geneflow and Gene diversity were 0.4840 and 0.1058, respectively, indicating that certain degree of gene flow was present in Z. insignis provenances and the degree of genetic differentiation was medium. Genetic variations among provenances accounted for 34.03% of total genetic variations, and the genetic variations of 65.97% distributed in individuals of Z. insignis.Genetic distance and geographic distance matrices were not significantly correlated, while the PPB and leaf morphological characters were significantly correlated, and Shannon's Information index, Nei's index and growth characteristics were significantly correlated. While all these indexes were not correlated with physiological index of cold resistance, thus it could come to the conclusion that the cold resistance of Z. insignis was controlled by some specific genes. According to cluster analysis, Z. insighnis provenances were divided into four groups. GroupⅠ:Yingde, Xincheng and Tongdao provenances. GroupⅡ:Jingxi provenance. GroupⅢ:Xingyi provenance. Group IV:Jianghua provenance. There existed geographical isolation among the four groups, which is consistent with geographical distribution patterns.