Studies on the Developmental Responses of Tobacco Seedlings in Relation to their Age. : V. Effects of diurnal variation of temperature upon the developmental responses of tobacco seedlings.

Abstract

In the previous paper (IV) it was reported that plants cultivated at the field belonging to Utsunomiya Tobacco Experiment Station produced greater number of leaves than those at the field belonging to Okayama Tobacco Expriment Station and that daily mean temperature was little different, however the diurnal variation of temperature was greater in the former than in the latter. Then studies were made on effects of diurnal variation of temperature upon the developmental responses of tobacco seedlings. Seedlings with 9 to 12 leaves of Hicks I-2 variety were used. In experiment I two temperature treatments were designed under 12hrs. day-length condition. In one of them daily mean temperature was 16°C and the diurnal range of it was 24°C. In the other, temperature during lightperiod was the same as the former, but temperature during dark-perid was higher by 9°C. Then the effect of temperature during dark-period upon the developmental responses was examined. Plants grew at higher rate and bore greater number of leaves under warm night than those under cool night. In experiment II three treatments on temperature were designed under 12hrs. day-length condition. Daily mean temperature was 16°C in all treatments. One was constant temperature (16°C), the others had the diurnal variation of temperature varied 23-9°C and 28-4°C respectively according to sine curve. The highest rate of leaf initiation was observed in the variation 23-9°C Plot and the lowest one in the variation 28-4°C Plot. In both the constant temperature Plot and the variation 23-9°C Plot, leaf initiation rate was slower with increasing of seeding-age at the beginning of treatment, however it differed little in the variation 28-4°C Plot. Plants bore the least number of leaves in the constant temperature Plot. In the variation 28-4°C Plot plants produced greater number of leaves than those in the variation 23-9°C Plot. Seedlings with more number of leaves at the beginning of treatment initiated floral primordia earlier, however little difference in total leaf number at flowering was observed in all plots.