STUDY ON THE METHOD OF EVALUATING THE TOLERANCE TO LOW TEMPERATURE OF CHINESE CABBAGE(Brassica Campestris,ssp.)COLLECTED DURING ITS SEEDLING PERIOD

Chinese Cabbage (Brassica campestris,ss p.) originates from Shandong and Hebei provinces of China, so it adapts to grow in wet and cool climate, and is sensitive to high temperature and chilling. Although it has some tolerance to the low temperature, its growth and development are greatly affected by it, especially for the Chinese Cabbage which is sowed in hot houses or plastic sheds in winter or spring and picked during the seedling period with eight or nine leaves on it. Under low temperature, Chinese Cabbage is injured and its growing rate reduces, sometimes even stopping growing. It is necessary to secreen the strain of Chinese Cabbage, which grows fast in low temperature during its seeding period. The screening is completed by the seeds, the growing characteristic and physiological biochemical indexes of Chinese Cabbage during different growing periods of its seedling and its correlation with the production under low temperature. The experimental result is as follows: 1. The appropriate appraising temperature of Chinese Cabbage in germination is set 10 C, so germination index in 1CC can be used to appraise the low-temperature tolerance of the Chinese Cabbage. It has a significant positive correlation with the production under low temperature, so it is also used as an index of production. Although the activity of POD and the soluble sugar content of the Chinese Cabbage seeds treated in low temperature decrease, they have no significant correlation with their low-temperature tolerance during germination. 2. During seedling period, the activity of POD and CAT is generally higher than its control抯, and the soluble sugar content is obviously higher than its control抯. With the extention of the low-temperature treatment, the soluble protein content shows a V-shaped change and the electric conductivity rate presents an increasing tendency. The contents of proline~ MDA and chlorophyll have no obvious tendency. 3. The increasing rate of the fresh leaves weight during their four-leaf growing period growing in I S 慍/iCC which has a significant positive correlation with the production, can be used as another production index. The activity of POD, which has a nearly significant correlation with the production, can be used as an auxilIary low-temperature tolerance index. So is the increasing rate of the fresh leaves weight during their two-leaf growing period growing in 1 /I O扖. 4. The Chinese Cabbage抯 low-temperature tolerance during germination has no 2 2OOI~5.~ difference with its low-temperature tolerance during seedling. The germination index has a significant correlation with the increasing rate of the fresh leaves during its two-leaf growing period growing in I 5C/I &C and a nearly significant correlation with the increasing rate of the fresh leaves during its four-leaf period growing in I 5C /1 0C. S. The secreening result is four strains of strong low-temperature tolerance and seven strains of weak low-temperature tolerance. Postgraduate: Guo Changlu Major: olericulture Supervisor: Prof Cui Chongshi...