Physiology and Biochemistry of the Tobacco Plant. 1. Growth and Development - Physiologie und Biochemie der Tabakpflanze: 1. Wachstum und Entwicklung

Growth and development processes of a tobacco plant affect the chemical composition of the leaf and therefore the usability of the leaf. Growth starts with the initial stages of germination and development stops with the cured leaf. Most tobacco seed will germinate in the dark and the first seeds to germinate from a seed lot tend to produce larger plants for transplant and harvest. Nicotine is found in mature seed and increased rate of germination increases rate of nicotine accumulation in the young seedling. Carbon / nitrogen balance in the leaf is important for leaf usability and is influenced by available soil water and soil nitrogen. Oriental leaf is produced typically with limited water and nitrogen supply and the leaf contains large amounts of carbohydrates and ether solubles but small amounts of nitrogenous substances. Cigar filler tobacco is grown on soils with a plentiful supply of soil water and soil nitrogen and the leaf contains large amounts of nitrogenous substances. Intermediate to these tobacco types is flue-cured tobacco which is grown with limited soil nirogen but adequate water and the leaf is relatively thin with high carbohydrate content. Maximum rate of leaf expansion is achieved early in development of a leaf. In flue-cured tobacco phosphorus and potassium concentrations remain constant during growth, whereas nitrogen, calcium and magnesium concentrations decrease. In Oriental tobacco the concentrations of nitrogen, phosphorus, potassium and calcium decrease during the growing season. However, Burley tobacco accumulates relatively greater amounts of nitrogen, phosphorus and potassium during the first half of the growing season relative to dry matter accumulation. Maximum growth per unit leaf weight occurs 14 to 21 days after transplanting, whereas maximum dry matter accumulation per day occurs 50 to 55 days after transplanting. Leaf development including senescence is controlled genetically and decreased chlorophyll and protein and increased nicotine contents are important changes associated with leaf senescence. Maximum nicotine content of leaf occurs at successively higher stalk positions as the plant matures.