Studies on the Developmental Responses of Tobacco Seedlings in Relation to their Age. : III. Effects of temperature in seed-bed and field upon the developmental responses of tobacco seedlings

Abstract

Effects of temperature in seed-bed and field upon premature blossoming of tobacco plants were examined. The flue-cured variety, Hicks I-2 was used. In expriment 1, 9-12th leaf seedlings were grown under two different seed-bed conditions. The one was the commercial seed-bed covered with vinyl-film, the other a seed-bed set in a greenhouse. Minimum temperature was lower in the former by ca. 8°C as compared with that in the latter. These seedlings grown under different conditions were transplanted to the fiield and the same ones were transferred to the phytotron maintained at 20°C under natural day-length condition no April 8th in 1962. Plants cultivated in the fiield showed the same trends reported in the previous paper (I). The more advanced in age the seedling transplanted in the field, the earlier the flowering date, the lower the plant height and moreover the less number of leaves. But with plants transplanted from the greenhouse to the field, these trends were less observable. On the other hand, plants produced greater number of leaves in the phytotron than those in the field. And with plants cultivated in the phytotron, difference was not observed in total leaf number among seedlings with different ages, accompanying with no effect of the seed-bed condition upon the developmental responses of tobacco seedlings. These facts suggested that it was not day-length but temperature, especially in the field, that caused differences in total leaf number. In experiment II developmental responses of tobacco seedlings were examined in 1962 and 1964. Seedlings of 8-12th leaf stage cultivated in the commercial seed-bed were transplanted to the field on April 12th in 1962 and on April 13th in 1964 respectively. The same results as reported in the previous paper (I) were obtained in 1962. But in 1964, leaves were produced at higher rate and no difference in time for flower-bud formation among seedlings with different ages was observed. Consequently, plants bore greater number of leaves in contrast to that in 1962, and total leaf number increased with increased age of seedlings used for transplanting. The reason why these phenomena occured was able to be explained by comparing the changing pattern of diural mean temperature in both years. That is to say, in 1964 diural mean temperature was higher throughout the growing season as compared with that in 1962. But diural temperature rose gradually in 1962, and did not so in 1964. The development of tobacco seedlings was greatly influenced by temperature and the difference in total leaf number among seedlings with different ages arose chiefly from the changing pattern of diural temperature, which was confirmed in several experiments carried out by many procedures.