Abstract
This experiment was conducted to investigate varietal responses to cool temperature (18℃) and short photoperiod (8 hours a day) in a controlled room of phytotron. Five burley tobacco varieties (Nicotiana tabacum L.), Awelius (very early flowering type), Burley 21 and KB 103 (medium), Banket Al and MB 1 (slightly late) and TC 681 (late) were compared in number of leaves per plant and day to flower in different treatment periods (10, 15, 20, 25 and 30 days). The days to flower decreased significantly than the control (in the phytoron with 14hr photoperiods and a minimum temperature 20'c) when the treatment periods were over 15 days for the varieties Aurelius, Burley 21 and KB 103, and 20 days for TC 681, and 30 days for Banket Al, respectively. And also the number of leaves decreased significantly than that of the control when the periods of treatment were over 10 days for Burley 21 and Aurelius, 15 days form 103, and 20 days for TC 681 and Banket Al, and 30 days for MB 1, respectively. The decreasing ratio in the number of leaves per plant under cool temperature and short photoperiod treatments was the lowest in Banket Al and MB 1. Key words : Nicotiana tabacum, cool temperature, short photoperiod.