| Salt injury is one of major problems in pepper protected cultivation. Response mechanism and salt-tolerance mechanism of pepper against salt injury were investigated to make sure salt-tolerance indexes, improve salt-tolerance ability and screen salt-tolerant cultivars rapid and accurately. This investigation plays an important role in soil salinization cultivation, and at meantime, it has a great practical significance in sustainable development of vegetable protected cultivation.Four pepper cultivars ("lvzhoujiaoba","ribentianyingjiao","xinyouyihao","gaochanlajiaowang")were investigated in this paper, studied the effect of different NaCl concentration on pepper seed germination characteristics, then 40 cultivars were investigated to conduct germination test in salt water under single NaCl concentration, aimed at screening eight salt-tolerant cultivars( four strong salt-tolerant cultivars and four poor salt-tolerant cultivars). These eight cultivars were applied as the following experimental materials, investigating the salt injury influence on physiological and biochemical indexes of different pepper cultivars during bud or seedling stage, providing theoretical basis for screening salt-tolerant cultivars rapid and accurately and salt-resistant cultivation. The results revealed are as follows,1. Among the four cultivars of"lvzhoujiaoba","ribentianyingjiao","xinyouyihao"and"gaochanlajiaowang", vigor index of the four are higher than the control in relative low NaCl concentration (50~150 mmol/L). The number of lateral root decreased by 4.71%, 29.90%, 51.33%, 45.02% respectively, compared with the control. Germination potential, germination rate, germination index and root length of"lvzhoujiaoba"and"gaochanlanjiaowang"improved significantly compared with the control. High NaCl concentration (150~250 mmol/L) surpress the germination potential, germination rate, germination index, root length and the number of lateral root of the four in varying degree. Moreover, inhibiting effect of every index became stronger gradually accompanied with the increase of NaCl concentration,"ribentianyingjiao"and"xinyouyihao"decreased a little while"lvzhoujiaoba"and"gaochanlanjiaowang"decreased a lot. There are significant differences of these cultivars in germination potential, germination rate, germination index and vigor index when NaCl concentration was 200 mmol/L. Therefore, NaCl concentration of 200mmol/L was conducted as the right concentration of screening salt-tolerant pepper seedling.2. Indexes of 40 different pepper cultivars seed germination have been influenced by NaCl stress in varying degree. Relative germination potential, relative germination rate, relative germination index, relative vigor index, relative salt-injury rate, relative root length, relative fresh and dry weight of seedling in 40 different cultivars all decreased under NaCl stress, however, there were great difference among different cultivars. According to relative salt-injury rate,"niujiaojiao","guofengganxianwang","pilizaoguan","xinyouyihao","dubatianxia","qianjinhuangjiao","bihaihong", and"88dajiao"were selected as strong salt-tolerant cultivars, while"ainong6","chaojijufeng301","chaojihangjiao1","juangu","hongshengyou","gailiangtedazhongliu"and"dayunongda40tianjiao"were poor salt-tolerant cultivars, and"nongzhuangjixiang","nongzhuangjinjiao","tianxiadiyijiao","8819xianjiao","dongfangjiaoba","dongfangzhizun","jiangnanxiaojiaowang","fengyou8","gaochanlajiaowang","laboshi8","yiduhongganjiaowang","ribentianyingjiao", "ribenchaotianjiao", laboshi2","xinla4"were common salt-tolerant cultivars. Relative germination index and relative salt-injury rate are appropriate as screening salt-tolerant indexes of pepper germination.3. Physiological indexes of different salt-tolerant pepper cultivars in seedling stage were investigated under 200mmol/L NaCl stress. Results showed that, the inner membrane lipid peroxidation product MDA content and relative conductivity of strong salt-tolerant cultivars increased by a little more than the poor ones under NaCl stress; the content of osmotic substances such as free proline, soluble sugar, soluble protein and so on were still on the rise, but rise a little. The SOD and POD activity of the strong salt-tolerant cultivars kept at higher level under NaCl stress, while the poor ones were on the contrary. MDA, relative conductivity, SOD and POD activity can be regarded as salt-tolerance indexes of different pepper cultivars, while free proline, soluble sugar and soluble protein were not appropriate for that.4. Physiological indexes of different salt-tolerant pepper cultivars in seedling stage were investigated under 200mmol/L NaCl stress. Results showed that, the growth of pepper seedling was suppressed in varying degree with prolonging of NaCl stress time. These indexes included plant height, root length, dry and wet weight of above-ground, dry and wet weight of root of the strong salt-tolerant cultivars decreased, but decreased less than the poor salt-tolerant cultivars. The content of osmotic substances such as free proline, soluble sugar, soluble protein and so on were all on the rise, but rised more than the poor ones. With prolonging of NaCl stress time, the inner membrane lipid peroxidation product MDA content of poor salt-tolerant cultivars increased, and membrane permeability increased, selectivity of methane decreased, plasma membrane injury increased, while the inner membrane lipid peroxidation product MDA content and membrane permeability of the strong ones increased less than the poor ones. The chlorophyll content, SOD and POD activity of pepper seedling were influenced by prolonging of NaCl stress time in varying degree. SOD and POD of the strong salt-tolerant cultivars kept with higher activity under NaCl stress, while the poor ones were the lower. Therefore, the increase of enzymatic activity was in proportion to salt-tolerance. Plant height, fresh and dry weight of above-ground, membrane lipid peroxidation product MDA content, relative conductivity, SOD and POD activity can be regarded as salt-tolerance indexes of different pepper cultivars, while root length, fresh and dry weight of root, free proline, soluble sugar, soluble protein and chlorophyll were not appropriate for that.In a word, this paper demonstrated the salt-tolerance of different pepper cultivars, and established the screening indexes of salt-tolerant pepper, however, there are still some other physiological indexes such as soluble sugar, proline and chlorophyll need to be researched.
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