Mechanisms and management of premature flowering in flue-cured tobacco

The nutrient diversion hypothesis of flowering states that the controlling factor in floral initiation is an imbalance in carbohydrate and nitrogen translocation from the plant to the apical meristem. Experiments were conducted in the phytotron to determine the association of plant carbohydrate and nitrogen levels in the apical meristem and floral initiation of flue-cured tobacco. Low temperature, nitrogen withdrawal, and restriction of nitrogen uptake were used as treatment variables. All of these stresses induced flowering at a lower number of leaves as compared to control treatments. Low temperature stress accelerated the time of flowering as compared to a high temperature control; however, nitrogen stress did not accelerate the time of flowering. All stress treatments affected the levels of nitrogen and carbohydrate in the plants. Most notable was an increase in the percentage of starch and a decrease in the percentage of total soluble carbohydrates induced by the stress treatments. These data indicted that tobacco plants under stress accumulate excess carbohydrates, which are stored in the form of starch. An imbalance in relative carbohydrate and nitrogen transport to the apical meristem was observed in all treatments at the time of floral initiation and is in support of the nutrient diversion hypothesis of flowering.; Field experiments were conducted to determine a threshold level of premature flowering in flue-cured tobacco (Nicotiana tabacum). Seven levels of premature flowering were simulated by mixing plants induced to flower in a controlled environment with plants which were produced under non-inductive conditions. At flowering levels below the threshold, yield and quality would not be expected to be less than that where premature flowering did not occur. Special management techniques, such as removal of the inflorescence and allowing the development of only one axillary bud, would not be required below the threshold. The data indicate that premature flowering levels as high as 70 percent did not reduce cured leaf quality. Yield was not significantly reduced below 15 percent premature flowering, at which level the threshold was established. After preharvest removal of all but one axillary branch, the number of leaves per plant was not affected by any level of premature flowering. Weight per leaf was reduced on plants which flowered prematurely. Of the management techniques evaluated, the traditional management of removing non-expanded leaves and allowing the development of one axillary branch was superior at premature flowering levels above 15 percent.