EFFECT OF CONSTANT TEMPERATURES AND NATURAL DAYLENGTH ON FLOWERING TIME AND LEAF NUMBER OF ANTIRRHINUM USING THE PHOTO-THERMAL MODEL

Abstract

After 80% seed germination plants of an early flowering cultivar Chimes White of Antirrhinum were subjected to five set-point temperature regimes (14, 18, 22, 26 and 30°C) for two consecutive years to observe their effects on the flowering time and leaf numbers using photo-thermal model. Findings revealed a curvilinear response of flowering time to temperatures that is plants flowered after 34 (31.8°C), 35 (25.3°C), 37 (23.1°C), 43 (19.5°C) and 68 days (14.6°C) of transplantation in 2002 whereas in 2003 flowering time was recorded as 30 (31.5°C), 29 (27.5°C), 34 (24°C), 39 (22.5°C) and 67 days (15.1°C). Similarly, rate of progress to flower per day was increased linearly up to plateau at 28°C set-point temperature, thereafter, no changes in rate of progress to flower is observed which indicated that 28°C is the ceiling temperature for the flower initiation and development of cultivar Chimes White. A three to six days difference in flowering time was observed below ceiling temperature which might be due to the difference between the light integrals (0.9 MJ.m-2.d1 ) in two years. Non-significant difference was observed regarding leaf numbers data in both years i.e. 9-10 leaves in 2002 and 8-9 leaves in 2003. Predicted data estimated from the photo-thermal model plotted against the actual data which showed a best fit, hence, the model application is validated which would assist growers to use it for plant scheduling.