| Summary: | 博士 === 國立臺灣大學 === 園藝學研究所 === 88 === Investigation and Evaluation of Plant Characters and Establishment of Dwarfing Pear Selection Model of ‘Bird’ Pear Seedlings (Pyrus sp.)
Abstract
Open pollinated ''Bird'' pears were collected from Chuo-lan, Da-hu and San-wan for a series of experiments. The experiments were to be conducted by the order of (1) to survey fruit characters, (2) to conduct seed germination experiment, (3) to survey and assess the growth and the development of the seedling, (4) to evaluate the stability and relationship between plant height and other plant traits within three years, (5) to select the seedlings with dwarf characters, and (6) to establish dwarfing selection model of ‘Bird’ pear.
The fruit collected from Da-hu had the largest fruit size, the most numbers of seeds and the heaviest fruit weight, which was followed by San-wan’s fruits and then the Chuo-lan’s fruits. San-wan’s fruite had the smallest seed size and Da-hu the largest. Seeds of Chuo-lan and Da-hu, sown in natural conditions had an extremely low germination rate and a much longer germination period. This situation can be improved if the seeds are stratified under 4℃ for several days. Germination conditions will be greatly improved if the seeds can be stored under 4℃ for more than ten days. Growth characters varied among the three groups of seedling population, particularly the seedlings from Chuo-lan that could be divided into two groups according to the plant height. The frequency distributions of the plant height of seedlings from Da-hu and San-wan were close to the normal distribution. After a three-year survey, the results showed that the plant height of the second year was higher than that of the first year, and all of the population had the same performance of frequency distribution and tendency. The plant from Chuo-lan had the highest plant height and the most branches. The plant from Da-hu had the shortest plant height and the fewest branches.
To understand the relationship between each plant’s characteristics and the plant height, the characters of ''Bird'' pear seedlings in the three areas were correlated and by regression analyses. It was found that the characters of seedlings were related to the plant height. Most of the characters had positive correlation with the plant height except for the bark and the trunk diameter, which were in negative correlation with the plant height. The result of the first year showed that the trunk diameter had a strong correlation with the plant height, though the number of nodes had a strong correlation with the plant height after the second year. In the third year the highest correlation with the plant height was found to be with the number of nodes. The correlation coefficient for Chuo-lan was 0.956, 0.917 for Da-hu, and 0.937 for San-wan. The second highest correlation with the plant height was the trunk diameter. The correlation coefficient was 0.865 for Chuo-lan, 0.870 for Da-hu, and 0.907 for San-wan. For most of the other characters, the correlation coefficients stayed under 0.7 in all three lines except from the characters of the length between nodes and the trunk cross-section area. The two characters had slightly higher correlation coefficients with the plant height, around 0.66 to 0.84. The number of thorns and branches showed large differentiation between the three lines, hence these characters should be considered as essential variables to be correlated with the plant height.
In order to investigate the stability of plant characteristic performances in each year, the plant heights in three years and the one-year plant height were cross-examined with the plant characters of another year by simple regression analysis and forward stepwise regression analysis. Most characters were stable except that the node numbers and the branch numbers were cross-examined with the plant height of another year. The credibility and correlation were confirmed through an interval of two years rather than one, and the stability increases with an increasing age of the plant. The instability in the correlation between the node numbers and the plant height was probably caused by the growing environment and the plant age. Trunk diameter, length of inter-node, and trunk cross-section area were stable characters.
The forward stepwise regression analysis in three years showed that plant height of an interval of one year is much greater than that of two years, hence the plant height in the second year is a decisive year. Stability compared among the three areas showed that San-wan had the most stable overall correlation ratio of plant characters and plant height.
The open pollinated seedlings of ''Bird'' pear from Chuo-Lan and Da-hu areas were planted in 6-inch pots and treated under 5 ℃ for two weeks. Then the seedlings were placed in various environments with different day/night temperatures at 30/25 ℃, 25/20 ℃, 20/15 ℃, and 15/13 ℃ (day /night ℃), together with the control group that are treated in field conditions. At the beginning (within 100 days) the growth and growth rate of the seedlings increased with an increasing temperature. Both of the growth rates of the group treated by the day/night temperatures above 20/15℃ and the control group decreased sharply. The growth rate of the seedlings treated by the day/night temperatures of 15/13 ℃ either remained steady or increased slightly, which reached the largest plant height. The number of node under different treatments remained the same. The length of inter-node decreased significantly with an increasing temperature. Also, the trunk diameter, the cross-section area of the trunk showed simple regression and the number of thorns and branches varied with different treatments. High multiple regression coefficients between the plant height and the number of nodes, the length of inter-node, the trunk diameter, and the trunk cross-section area were found in all treatments in the plants collected from Chuo-lan. Temperature seemed to affect more on the correlation between the plant height and other characters of the plants collected from Da-hu. The results had shown that the performance of phenotypes was quite different between the ''Bird'' pear seedlings from Chuo-lan and Da-hu. It was also shown that some plant characters were affected by temperature. Therefore various temperature treatments are required to understand the performance of plant height.
Through field growth data, field survey, regression, and correlation analysis, 44 ''Bird'' pear seedlings were selected. The chosen seedlings were grafted on to ''Bird'' pear cutting. The growth characters of grafted sapling, the three-year data of growth characteristic of the original seedlings together, and the confidence and prediction intervals determined the distribution of selected seedlings in the population. In addition, the ranking method was used to evaluate the stability in each year. By taking the average of the selected seedlings as the center point and 0.4 the standard deviations of the class interval between each rank, the selected seedlings were divided into nine ranks. The results of the re-evaluation of the nine ranks provided further information in the selection and evaluation. According to the data, 20 plants and 5 plants for control were selected for further tests.
By utilizing the calculation, the logical function, graphs, and filtering functions in ‘Windows Excel’, it was possible for the ideal selection of the seedlings for dwarfing pear trees. Through programming, it is possible to reduce workload and improve in accuracy in the data processing of complicated experiments.
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