| Rapeseed (Brassica napus L.) is one of the most important sources of vegetable oil and protein rich meal in the world. Because of frequent seasonal autumn drought occurring, rapeseed production in China is often disturbed. It is an effective pathway for withdraw drought stress to screen idioplasmic resource and breed variety with drought tolerance. According to germination percentage, hypocotyl length, fresh weight and DTI, present study evaluated drought tolerance of 81 varieties of Rapeseeds (Brassica napus L.) from different genetic resources during germination stage with simulate water stress by 10% (w / v) PEG6000. Wither percentage as the key parameter combined photosynthesis, leaf, root were observed to screen out some varieties with drought tolerance from 17 rapeseeds. And Zhongshuang No.10 was used to explore role of GA3 priming with concentrations in improving drought tolerance of germinating seeds in rapeseed.Drought tolerance of 81 varieties of Rapeseeds from different genetic resources was investigated during germination stage with simulate water stress by 10% (w / v) PEG6000. The results showed that the germinating traits of several treatments were significantly different from control after drought stress. The average seedling height of treatment deceased 36.5%, the average fresh weight decreased 31% and relative germinate rate decrease 11.1%. There was significant difference of drought tolerance among different varieties or lines. The vigor index of seedling ranges from 19% to 81%, the average relative vigor index is 55%. Correlation analyses indicated that the vigor index has significant positive correlation with the seedling traits under drought stress. Some varieties or lines, 30295, 30253, Zhongshuang No.6,30703, 30296, 30290, 30704, Zhuongyouza No.9 and Deyou No.4, could be classed as high drought tolerant germplasm resources with higher vigor index.It is positive to evaluate rapeseeds varieties with high drought tolerance in 17 rapeseeds seedling under water stress, we study the physiological variance and the method to evaluate drought tolerance. It is difference to keep water statue, photosynthesis, antioxidants activity in 17 varieties under drought. As higher LWI as lower decrease of Pn, chorophyll, caroternoid content and increase of WSD, MDA content, electrolyte leakage were in 17 varieties. Moreover, there was significant correlation between antioxidants (SOD) activity and LWI. LWI is an easy and general parameter to reflect drought tolerance in rapeseed seedling. Third degrees of drought tolerance and B108,H3531,Q2,9548,8056 with high drought tolerance were evaluate by LWI in 17 rapeseeds.The role of gibberellic acid-3 (GA3) to improve drought tolerance in rapeseed was evaluated. For priming, seeds of rapeseed (c.v. Zhongshuang No.10) were soaked in 0, 100, 200, 300, 400 and 500 mg·l-1 aerated solution of GA3 for 8 h. The primed seeds were sown to germinate for 7 days under a simulated drought stress by applying 15% PEG6000 solution. The result showed that GA3 can significantly improve seed germination characteristics under drought stress. Compared with controls, priming seed with 300 mg·l-1 GA3 significantly increased drought tolerance index by 88%, fresh weight by 42.9% and hypocotyl length by 72.7%. GA3 treatment also increased soluble sugars significantly by 47.2%, soluble proteins by 35.6%, free proline by 62.9%. The level of oxidative damage was reduced significantly with lower electrolyte leakage (decreased by 36.5%) and malondialdehyde (MDA) content (decreased by 36.6%), possibly due to the enhanced superoxide dismutase (SOD) (increased by 13%), catalase (CAT) (increased by 45.6%) and peroxidase (POD) (increased by 46.6%). The result of this research showed that GA3 is an effective regulator to boost seed germination of rapeseed and improve seedling tolerance to drought stress.
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