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Effects of Deficiency and Excess Boron on Nicotine, Phenols and Sugar Contents of Sun-cured Tobacco

ABSTRACT Boron (B) is an essential micronutrient required by plants, and deficiency or toxicity of B causes several biochemical and physiological disorders in plants. The aim of this study was to investigate the effects of B applications on leaf yield and chemical quality of three different tobacco varieties (Nicotiana tabacum L.) grown in a B-deficient soil. The increase in B doses had a significant effect on leaf yield, B and nitrogen concentrations, nicotine, chlorogenic acid, rutin and sugar contents of leaves. Leaf B concentrations of tobacco cultivars significantly increased with increasing B doses. Leaf yield, nitrogen and nicotine concentrations increased up to 4 mg B kg−1 application in Canik and Xanthi-81 cultivars and up to 1 mg kg−1 in Ozbas cultivar, while all decreased at higher B application doses. Nicotine contents of tobacco cultivars significantly varied with B applications, and the highest nicotine content was obtained in Canik (0.47%) and Xanthi-81 (0.48%) cultivars at 4 mg B kg−1, and the highest nicotine content in Ozbas cultivar (0.51%) was recorded in 1 mg B kg−1 application. The results revealed that 4 mg B kg−1 dose for Canik and Xanthi-81 varieties and 1 mg B kg−1 for Ozbas cultivars can be recommended to obtain optimum tobacco yield and leaf quality. B application doses lower than the aforementioned values may cause B deficiency, while higher values may cause toxicity.