Developmental Response of Tobacco Plant to Temperature in Relation to Photoperiodic Condition

Abstract

This study was planned to make clear whether the promotive effect of low temperature on the flower bud initiation in tobacco plants is exerted more in diurnal dark period or in light period. The material used was Bright Yellow, a Virginian variety, which had been grown in an air-conditioned glass-house under various photoperiod. The detailed design of experiment is given in Table 1. The results may be summarized as follows: 1) By the 1st experiment, wherein 12hours' light and dark period were alternated at either high (25°C) or low(13°C) temperatures, it was observed that the plant maintained constantly at the temperature initiated first the flower buds, while next was that grown under the low temperature for the light period and last was that under the high temperature for the dark period. No marked difference in response was recognized between the plant under the costant high temperature and that under the high temperature only for the light period. 2) Exposures to different lengths of illumination from 8 to 14 hours at constant high or low temperatures were given in the second experiment. It was proved that under the low temperature developmental response was accelerated regardless the day-length, while under the high temperature it was decidedly retarded under 12 or more hours' illumination, though not so much under 8 hours' illumination. 3) An experiment of various combinations of the length of photoperiods and the height of temperature was also performed. The result was that, the plant development was promot d by the low temperature for dark period regardless the day length just as by the constant low temperature. And the plot maintained at the high temperature during 8 hours' illumination and at the low temperature for dark period reached its flowering stage as rapidly as those which were subjected to the low temperature for light period or as that subjected to constant low temperature. On the other hand, the imilar plots illuminated however for periods longer than 8 hours showed retardation of bud formation. 4) The above results may suggest the fact that the promotive effect of low temperature upon flower initiation in tobacco plants is remarkable at a light period than at a dark period.