Studies on the Developmental Responses of Tobacco Seedlings in Relation to their Age : IV. On the differences of the developmental responses of tobacco seedlings among the areas with different climatic conditions.

Abstract

In the previous paper (I), the authors reported that in Setonaikai districts premature blossoming was frequently observed in tobacco plants transplanted at the age of 11th or 12th leaf. On the other hand, premature blossoming is scarcely observed in the Kanto provinces or the areas among Tyugoku Mountains. This experiment was carried out to make clear the causes of local differences of the developmental responses of tobacco seedlings. Three fields, which belonged to Kagoshima, Okayama and Utsunomiya Tobacco Experiment Station respectively, were selected with an eye on the different climatic conditions. Seedlings with 9 to 11 leaves of Hicks I-2 variety cultivated under the control condition (20-30°C, 12hrs.-light period) were sent from Okayama Tobacco Experiment Station to the other two experiment stations by rail in 15-20 hours. On April 2nd in 1963 these seedlings were transplanted to Okayama and Kagoshima fields and on April 17th in 1963 to Okayama and Utsunomiya fields at the same time. In the Kagoshima field leaves initiated at higher rate and plants bore greater number of leaves than those in the Okayama field. No difference in total leaf number among seedlings with different ages used for transplanting was observed in both fields. Temperature was higher in the Kagoshima field than that in the Okayama field throughout the growing season. Astronomical day-length in both fields differed little. Then it was thought that these differences in the developmental responses arose chiefly from temperature different among these two fields. Interdiurnal change of temperature was irregular in both fields, that caused no difference in total leaf number among seedlings with different ages used for transplanting. In the Utsunomiya field leaves initiated at lower rate than in the Okayama field. In the former however, plants bore greater number of leaves than those in the latter. Difference in total leaf number among seedlings with different ages used for transplanting was observed in the Okayama field, but not in the Utsunomiya field. Both astronomical day-length and daily mean temperatute were scarcely different among these two fields. However the diurnal variation of temperature differed; the diurnal range of it was greater in the Utsunomiya field than in the Okayama field. It was supposed that longer time of low temperature at night depressed the leaf initiation and longer time of high temperature at daytime retarded the flower-bud formation of tobacco seedlings in the Utsunomiya field.