CAUSES OF EARLY FLOWERING IN TOBACCO

Two factors believed to be involved in the early flowering of tobacco, the timing of transplanting relative to seedling development, and the effects of low temperature, were investigated. Early flowering in the field appeared to be due to the occurrence of floral induction in the seed-bed. If the shoot apex became irreversibly committed to flower before transplanting, flower initiation at a low node took place soon afterwards. The risk of floral induction in the seed-bed increased with seedling age, but diminished if the seedlings were retarded through drought. In controlled conditions, ripeness-to-flower of a short-day cultivar was judged to be dependent on the attainment of a minimum plant size corresponding to a minimum leaf area of about 25 cm2, and was reached sooner at 30/25 than at 20/15°C. Floral induction, however, proceeded more quickly at the lower temperature. The minimum effective inductive period was fO days, after which floral differentiation was quicker at the higher temperature. Thus the plant’s response to temperature depended very much on its stage of development. © 1969 CSIRO. All rights reserved.