Effects of brassinolide and auxin on growth, carbon and nitrogen metabolism and tobacco quality of flue-cured tobacco leaves after topping

A field experiment was conducted in Jiyuan Tobacco Area of Henan Province, to study the effects of brassinosteroid (BR) and auxin (indole acetic acid, IAA) on growth, carbon and nitrogen metabolism and leaves quality of flue-cured tobacco. The aim of the experiment was to explore the rational managements of flue-cured tobacco after topping in the study area. The experiment included 6 treatments, which were spraying water (T1), spraying 10 mgkg^-1 BR (T2), spraying 10 mgkg^-1 IAA (T3), spraying 20 mgkg1 IAA (T4), spraying 10 mgkg^-1 IAA and 10 mgkg^-1 BR (T5) and spraying 20 mgkg^-1 IAA and 10 mgkg^-1 BR (T6), after topping of tobacco. The area of the top 5 leaves, dry matter of different organs of flue-tobacco were investigated at the day of topping, 15 days and 30 days after topping, the activities of enzymes relative to carbon and nitrogen metabolism of flue-cured tobacco were investigated at the day of topping and 10 days, 20 days, and 30 days after topping. The results showed that: 1) spaying BR and IAA after topping promoted leaves expansion, root growth, upper leaves production. Combined spring of BR and IAA showed better effect. 2) Under BA and IAA treatments, nitrate reductase and glutamine synthetase activities first raised then dropped, while invertase and amylase activities first decreased then slightly increased. This suggested that spaying BR and IAA after topping enhanced carbon and nitrogen metabolism, delayed tobacco maturity and fall time of yellow to a certain extent. Correspondingly, the growth period of tobacco with BR and IAA spraying was extended. 3) Spaying BR and IAA after topping effectively increased potassium content, potassium- chlorine ratio and organic potassium index of tobacco leaves. The nicotine and chlorine contents of middle and upper leaves were reduced by spraying BR and IAA, especially for the upper leaves. Applying both BR and IAA at the same time showed best effects on leaves quality. 4) Among five BR and IAA treatments, T6 (IAA 20 mgkg^-1 + BR 10 mgkg^-1) was best for tobacco growth and leave quality improvement. Compared with treatment T1, treatment T6 increased potassium content, potassium-chloride ratio and organic potassium index by 40.9%, 68.5% and 0.524; decreased contents of chlorine and nicotine by 16.2% and 16.3% of the upper leaves, respectively. From these results, it was conclude that spaying BR and IAA after topping promoted growth, enhanced carbon and nitrogen metabolism, improved production and quality of flue-cured tobacco. Spraying IAA 20 mgkg1 + BR 10 mgkg1 was the optimum for tobacco cultivation of the study area.