Mechanism And Combining Ability Analysis Of Drought Tolerance During Germination In Brassica Napus L.

Rapeseed is one of the major oilseed crops in China. Drought has threatened the production of rapeseed. Breeding for rapeseed drought tolerance is one way of reducing lost of water deficiency. Different concentrations of Polyethylene glylol (PEG) are chosen to simulate different drought degrees which seedling stage rapeseed encounters and Zhongshuang No.9 is taken as material in this experiment. The concentrations of PEG are 0%,5%,10%,15%,20%,25%,30%. Length of taproot,seedling height,fresh weight per plant,electrical conductivity,survival rate and relative vigor index was measured in simulated drought stress. 10% PEG-6000 is the optimum concentration used to simulate drought stress mainly according to relative vigor index and survival rate together with the other indexes. Relative vigor index reflects traits related to germination and growth directly and synthetically, it could be used as a major index for drought tolerance identification.The effects of drought stress simulated by 10% polyethylene glycol 6000 (PEG-6000) on physiological and biochemical traits of 14 rapeseed varieties (Brassica napus L.) were studied during germination stage. Six indexes were determined, which relate to drought tolerance of 14 inbred lines: MDA content, soluble protein content, soluble sugar content, proline content, and six indexes which present seedling growth such as relative electrical conductivity,seedling height,fresh weight per plant,survival rate,numbers of adventitious roots and length of taproot were measured. The results showed that relative vigor index of seedling varied between 0.32-0.79, and relative vigor index of 14 varieties was 0.49 on average. Drought stress affected significantly (P<0.01) seedling height, fresh weight and survival rate. Compared with control (water), 10% PEG-6000 treatment decreased seedling height by 40.68%, fresh weight by 34.2% and survival rate by 18% on average. Also, malomdiadehyde (MDA), soluble sugar, proline, soluble protein content, and electrical conductivity of rapeseed seedling increased significantly. Compared with control (water), 10% PEG-6000 treatment increased the content of MDA by 96.7%, soluble sugar by 75.0%, proline by 2204.9%, soluble protein by 56.2% and electrical conductivity by 34.8% on average. But there were not significant differences between PEG treatment and control on numbers of adventitious roots and length of taproot.The breeding of rapeseed cultivars resistance to drought is one of the most important ways to reduce yiled loss in autumn. Combining ability and heritability of six drought tolerance indexes were investigated with a method of complete diallel crossing design in seven different drought tolerant cultivars. The parent lines and F1 were treated by 10% PEG, and then relative seedling height, relative value of fresh weight per plant, relative survival percentage, relative germination rate, relative germination energy, relative vigor index of cultivars were measured, general combining ability and special combining ability of germination traits were analyzed by GriffingⅠ. The results showed that general combining ability was significantly different in 6 drought resistance traits. While special combining ability in 5 drought tolerant traits was significantly different except relative vigor index. In Zhongshuang 9, the general combining ability effect value of relative seedling height, relative value of fresh weight per plant, relative survival percentage, relative germination rate, relative germination energy and relative vigor index of varieties were 0.0708, 0.0656, 0.1185, 0.1048,0.1096 and 0.0861, respectively, and there was a high value of general combining ability of germination ability related traits. Although the general combining ability of Zhongshuang 6 wasn't very high, the special combining ability of its combination Zhongshuang 6×Xinongchangjiao and Zhongshuang 6×Zhongshuang 10 were the highest, and could be used in drought tolerance breeding.