Physiological Studies on Flower Formation of Tobacco : IV. Promoting effect of water-logging in rooting soil on flower formation of tobacco varieties with low sensitivities to temperature and day-length

Abstract

In this paper, the effect of lack or air in the rooting zone of the soil on flower formation is reported. Five varieties of Nicotiana tabacum, Bright yellow (a flue-cured tobacco, highly sensitive to low temperature and short photoperiod), Hicks Broadleaf (a flue-cured tobacco which resembles Bright Yellow), Xanthi (a Oriental or Turkish tobacco, non-sensitive to both conditions), Xanthi-Ova (similar to Xanthi), Xanthi-Yaka (another strain of Xanthi) and Cavalla (a day-neutral plant of a variety of Orient type which resembles Xanthi) were used in this experiment. Two groups of seedlings which had been grown by ordinary practice were selected from each variety at 11∼12 leave s stage and were transferred from the germination bed to soil tanks in the field. One of the seedling groups was then subjected to water-logging treatment starting from the time of transplantation. In this case, the tanks were continuously watered to the level of 2 cm above the soil surface. The other groups were kept without treatment for comparison. Both treated and non-treated plants were grown by ordinary practice under the weather conditions of May to August, day-length and mean daily temperature exceeding 14 hrs. and 18°C respectively. The results were as follows: In the treated plot, each variety flowered 7 to 10 days earlier than the corresponding variety in the control. Among the varieties promotion of flowering was most conspicuous in the variety Bright Yellow and Hicks Broadleaf. Moreover, in the varieies of the treated plot the total number of leaves per plant which had already been determined at the time of flower initiation, was less by 10∼22 leaves than the control. The data from four varieties of Oriental tobacco showed that flower formation in day-neutral plants can be accelerated by water-logging treatment. As it has already been proved that these plants do not respond either to low temperature or short photoperiod, the acceleration must be directly connected with the lack of air in the soil. The data from the variety Bright Yellow which is easily accerelated by both low temperature and short photoperiod also corroborate the above assumption because the experiment was conducted in summer under adverse conditions. From this point of view, it is very probable that soil aeration is as important for flower acceleration in tabacco as temperature and day-length.