Effects Of Light And Gibberellin（GA₃） Treatment On Seedling Quality And Their Growth, Yield And Quality Of Flue-Cured Tobacco After Transplanting

Seedling raising is the most important step in flue-cured tobacco production and the quality of tobacco（Nicotiana tabacum L.） seedling directly influences the growth, yield and quality of tobacco leaves. To cultivate the greatest stress-resistance seedling is the basis of high quality and yield of tobacco leaves. There are lots of reports on improving the quality of tobacco seedlings, but lack of the systematic study on light and gibberellin（GA₃） combination treatment to improve seedling quality and their field verification. In the present study, The lab greenhouse and field experiments were conducted using Yunyan 99 as material to study the effects of light and GA₃ treatment on quality of tobacco seedlings and their growth, yield and quality of flue-cured tobacco after transplanting. The main conclusions are as follows:1. The appropriate light intensity and GA₃ concentration could promote the tobacco seeds germination. Germination vigor, germination rate, germination index and vigor index of the tobacco seeds were increased but mean germination time was shortened with the increasing of GA₃ concentration under the same light intensity condition, while it was a decreases in the germination index and an increase in germination time when supplied at the high concentration of GA₃（over 100 mg·L-1）. In contrast, it showed a better promoting effect on seed germination with the light intensity treatment of 3700 lx under the same GA₃ concentration condition. In conclusion, it is beneficial for seed germination under 3700 lx light intensity together with 100 mg·L-1 GA₃ treatment.2. Different light quality and spraying GA₃ treatment could improve quality of tobacco seedling. Under the same GA₃ concentration condition, red light treatment（660nm） could enhance carbon metabolism amylase activity, increase the content of starch and soluble sugar content, while blue light treatment（450nm） could enhance nitrate reductase（NR） activity,soluble protein content and SPAD value and promote roots growth. Under the same light condition, stem height, maximum leaf length, fresh and dry weight of the whole plant and root shoot ratio were significantly increased, which could promote taproot and lateral root growth,increase root volume and root activity, enhance the key enzyme activities and metabolitessynthesis involved in carbon and nitrogen metabolism. The Comprehensive analysis showed that is held a significant improvement in enhancing quality of tobacco seedlings under the combination treatment of blue light（450nm） together with spraying 50 mg·L-1 GA₃ or red light（660nm） and spraying 50 mg·L-1 GA₃.3. In field, different light quality and spraying GA₃ in seedling stage was helpful for increases of tobacco stem girth thickening and leaf area. Moreover, yield, average price,percentage of superior tobacco, percentage of superior and medium tobacco, single leaf weight and output value of flue-cured tobacco were increased. There were enhancement in total nitrogen and potassium content, the ratio of nitrogen to nicotine and decreases in starch content, total sugar, nicotine content. The combination treatment of blue light（450nm） and 50mg·L-1 GA₃ concentration could promote greatly the seedlings growth and enhance the economic character and quality of flue-cured tobacco after transplanting.In this study, we investigated that the effects and physiological responses to single light or light and GA₃ combination treatments on promoting tobacco seed germination, improving seedling quality and yield and quality of flue-cured tobacco after transplanting. In conclusion,we conducted that the best combination treatment was blue light（450nm） and GA₃ treatment,which could provide an effective measure to improve the yield and quality of tobacco leaves through improving the quality of tobacco seedlings.