| Burley tobacco is an important material of blended type cigarette, and plays a crucial role in the formation of the Chinese-style cigarette. At present, many factors restrict the improvement of the quality of the blended cigarettes, such as fragrance inadequate, poor tenderness of tobacco smoke, single planting variety, production decrease and so on. Early growth and quick development of tobacco plants could relatively lengthen the plant growth period, increase dry matter accumulation, which is important for improving yield and quality of tobacco. However, early growth and quick development of tobacco plants often suffered from adversity stresses, such as low temperature and drought stress, and its physiological and molecular mechanisms were rarely reported. In this study, the field experiment was carried out in Enshi, Hubei Province, which is the main base for the production of burley tobacco in China. On the one hand, we compared the performance of the growth and physiological characteristics of burley tobacco under different cultivation model for revealing the mechanism of early growth and quick development of the burley tobacco. On the other hand, based on intrinsic characteristics of selected 10 domestic cultivation varieties, this study assessmented and screeninged burley tobacco varieties which suitable for the planting in Enshi area. Main results of the research were reviewed as follows:1. Mechanism of early growth and quick development of burley tobacco.Combined two breeding methods including stereoscopic breeding and floating breeding and two transplanting methods including well cellar transplanting and conventional transplanting, four different cultivating patterns were designed in this study. We found that stereoscopic breeding with well-cellar transplanting improved agronomic characters, photosynthetic rate and dry matter content of burley tobacco at different growth stages through field trials. The nicotine content was significantly reduced and decreased axtent in middle leaves reached 5.4%~23.5%, which resulted in better improved the tobacco leaf chemical quality. Increase of yield, output value and rate of medium-superior tobacco were 5.6%~30.0%, 7.9%~39.1%, 1.8%~13.3%, respectively. These results showed that cultivating pattern of the stereoscopic breeding with well-cellar transplanting could effectively promote early growth and quick development of burley tobacco. The result of variance analysis showed that, there was significantly interaction effect between breeding and transplanting, but it was not the main factor influencing economic yield and chemical component. Breeding methods were the main factors influencing yield, output value, rate of medium-superior tobacco and nicotine content, and the contribution rates were 64.1%, 62.4%, 63.0% and 63.4%, respectively. Transplanting methods were the main factors affecting total nitrogen content and its contribution rate was 68.0%. We investigated the mechanism through three aspects including active oxygen metabolism, endogenous hormone levels and nicotine synthesis. The results showed that the pattern of the stereoscopic breeding combined with well-cellar transplanting achieved the most significant results. In the aspect of active oxygen metabolism, the CAT and SOD activities were increased by 53.7% and 35.1%, respectively, and MDA content reduced by 29.3% compared to that in control patten of floating breeding combined with conventional transplanting at the rosette stage. Meanwhile Nt RCP1 which regulates antioxidant enzymes was up-regulated 2.2 times. The CAT and POD activities were increased by 38.7% and 28.2%, respectively, and the MDA content reduced by 35.3% at the maturity stage. Therefore, this cultivating pattern could improve the adaptability of tobacco plant to the cultivating environment and reduce the damage in aging process. In endogenous hormone level, the IAA concentration was increased by 16.5% and 17.2% at the rosette and vigorous growth stages, respectively. ABA concentration was decreased by 37.7% and 31% in vigorous growth and mature stage, respectively. Therefore it promoted the growth of tobacco plant in early stage and delayed the progress of plant senescence. Meanwhile, the rise of photosynthesis rate may be due to the decrease of ABA concentration which maintained stomatal opening. In the aspect of nicotine synthesis, the key genes of nicotine biosynthesis including PMT, QPRT, ADC and ODC were down-regulated 5.7 times, 4.4 times, 15.3 times and 22.5 times, respectively. These inhibited the synthesis of nicotine in roots and the transport to ground, an therefor the nicotine content in tobacco leaves was decreased.2. Regional suitability varieties screening of burley tobacco.In this research, 10 domestic cultivation varieties of burley tobacco were selected for field experiment in Enshi, Hubei, and then agronomic traits, dry matter accumulation, photosynthetic rate, active oxygen metabolism, leaf quality and economic yield of different varieties were analysised and compered. The results showed that, the variety Eyan 209 showed slightly better agronomic traits, dry matter content and photosynthesis, the maximum leaf area, leaf-number and dry-weight than the control variety Eyan 1. The plant height of Eyan 209 was increased 15.4%, and the photosynthesis rate and soluble sugar content were higher than the control variety at the vigorous growth stage. The agronomic traits, dry matter accumulation and soluble sugar content of Eyan 3, Eyan 6, Dabai 1 and Dabai 2 were lower than the control variety, and the photosynthesis rates of Eyan 3 and Dabai 2 were lower than the control variety at vigorous growth stage. Changes of active oxygen metabolism in the different varieties were complicated. CAT activity of Eyan 209 was increased by 37.5% and activities of SOD and POD had no difference compared with the control variety at rosette stage. Meanwhile, MDA content of Eyan 209 was slightly lower than the control variety in rosette and vigorous growth stages. The activities of antioxidant enzymes of Eyan 3 were lower than the control variety in each growth stage, and MDA content was higher than control variety in vigorous growth and mature stages. POD activity of Dabai 1 and Dabai 2 were lower than the control variety at mature stage, and MDA content was higher than the control variety. These indicated that the dominant effect of antioxidant enzymes were not fixed during different growth stages and there were complex interaction between them. Chemical quality of tobacco leaf had little difference among all varieties. Nicotine and total nitrogen content of Dabai 1 were much higher than other varieties and beyond the appropriate range. Sugar content of Eyan 209 and potassium content of Eyan 6 were higher than other varieties. The tobacco yields of all varieties were between 2200 kg/hm2 to 2600 kg/hm2, and output values of all varieties were between 35 thousand Yuan/hm2 to 50 thousand Yuan/hm2. Average price and rate of medium-superior tobacco had little difference among all varieties. Tobacco yield and output value of Eyan 209 were increased by 5.1% and 2.8% compared to Eyan 1, respectively. Tobacco yields of Eyan 3, Eyan 6 and Dabai were decreased by 6.0%, 7.7% and 9.1%, respectively, and output values were decreased by 10.3%, 11.2% and 12.2% than Eyan 1, respectively. Tobacco yield of Dabai 2 had no difference compared with Eyan 1, but the output value was decreased by 5.4%. Comprehensive evaluation on all varieties showed that the performance of Eyan 209 was better than Eyan 1 and could be used as alternative variety for demonstration and promotion. Eyan 211, Yunbai 1, Yunbai 2 and Chuangbai 1 had consistent performances with Eyan 1. Eyan 3, Eyan 6, Dabai 1 and Dabai 2 had significantly lower performance than Eyan 1 and not suitable for planting in Enshi. |
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