Study On The Relationship Between Changes Of Physiological Indexes Of Winter Rape (B.campestris L. And B.napus L) And Varieties Cold Hardiness Before Overwintering

The dynamic changes of physiological and morphological indexes of winter rape (B.campestris L. and B. napus L.) varieties and the relationship between these indexes and cold hardiness under different temperatures and natural overwintering conditions were studied through the indoor simulated experiment and the natural overwintering experiment in a field. All varieties of B.campestris L. and B. napus L. were classified based on their different cold hardiness using cluster analyses method. Meanwhile, the effect of cultivation measures on growth development and yield characters of B.campestris L. were studied.The main results were as follows: 1 When the treatment temperature descended in the nurture box, the relative water content in leaves of B.campestris L. and B. napus L. decreased , so the membrane relative penetration, malondialdehycle (MDA) content, soluble sugar content and free proline content showed a tendency of increase. All the tested indexes among varieties had no significant difference during 10℃~20℃period. While, the relative water content in leaf tissues of line876 and Tianyou2 of B. campestris L. decreased 14.9% and 16.53% respectively under 5℃, which was remarkably lower than that of other varieties (lines); the content of soluble sugar of the two varieties under 5℃were 7.2 and 5.2 times respectively than that of under 15℃; their content of free proline in leaf tissues obviously increased. So these two varieties were higher cold hardiness than others. But these characteristics were opposite to line 964, line 813 and Dongquan winter turnip rape. Under 5℃, the relative water content of Alice and Parade-2 of B. napus L. decreased to 11.90% and 10.61% respectively;the soluble sugar content were 6.55 and 4.91 times and their free proline content were 7.73 and 4.80 times compared with that of under 20℃. The membrane relative penetration and the malondialdehycle (MDA) content of these varieties, Ryder, Embleme and Olsen of B. napus L. rapidly increased. Correlation analyses indicated that cold hardiness of B.campestris L. and B. napus L. appeared negative correlation with membrane relative penetration and relative water content, the above simple coefficient were -0.919, -0.951. 2 During the overwintering period, the indexes of all varieties of B.campestris L. and B. napus L. changed. Malondialdehycle (MDA) content, cell sap concentration, soluble sugar content and free proline content of the leaves gradually increased with the decrease of relative water content in leaves before overwintering. And when the relative water content in leaves decreased minimum, the content of Malondialdehycle (MDA), soluble sugar and free proline in leaves and roots reached maximum. There were much soluble sugar and free proline content in the plant of line 867 of B.campestris L and Alice of B.napus L.. In early December, the soluble sugar content of line 876 reached to 23.72% in leaves and 24.25% in roots respectively, which were much significant difference than that of line 813 and line 964; at the same time free proline content of line 876 increased to 5.20mg.g-1FW in leaves and 9.65mg.g-1FW in roots. But to B.napus L, especially Alice, its soluble sugar content in leaves reached to 26.2%, 29.8% higher than Ryder, and free proline content reached to 7.78mg.g-1FW in leaves on the 5th of December. Comparing these two varieties,main indexes of cold hardiness of B. napus L .were higher than that of B.campestris L before overwintering, but B.campestris L had better adaptability to low temperature and chilling injury than B.napus L. because of creeping plant, growth-pot sink, and 8 to 9 leaves before overwintering. 3 The results of cluster analyses indicated that the 22 tested varieties of B.campestris L.and B.napus L could be divided into 4 cold hardiness groups based on their index character and cold hardiness. And the order of the survival rate were group II>group III>group I>group IV. All the characters of group II of B.campestris L. indicated superior cold hardiness: average relative water content was 79.33%, malondialdehycle (MDA) content was 4.76 nmol.g-1 FW, free proline content was 2.33 mg.g-1 FW; this group had suitable root length, great diameter of stem; average survival rate reached to 75.09%; also, there were some other good characters such as creeping plant, thin leaves, grow-pot sink and the average leaf age reaching to 9 to 10 main leaves before overwintering. And varieties of this group can be chosen as the best cultivation varieties in the cold area in northern China. Group III can also be extended and used in production after the cold hardiness adaptability was improved through low temperature acclimation and cold temper. 4 In order to reach high survival rate, it was suitable for winter rape (B.campestris L.) to be sown in middle or later August and controlled plant density between 600 thousand individual plants per hm2 and 900 thousand individual plants per hm2. And winter rape (B.campestris L.) mulched with different materials can increase seedling age and turn green early and shorten development period. Then, these measures can increase bolls per plant, develop sufficiency ramification. Besides, they can increase 1000-seed weight and improve yield finally.