Studies of the Effect of High Temperature on Growth and Developmental Response of Tobacco Plants : 1. Effect of various high temperatures on the flowering of tobacco plants

Abstract

Seedlings of flue cured tobacco were exposed to various high temperatures for short time in daytime, and their subsequent responses were observed. Heat treatments were conducted in each high temperature chamber maintained at 18 (check), 33, 38, 43 and 48°C for 2 hours in the experiment 1. And the temperatures of 26 (check), 48, 53 and 58°C for 3 hours in the experiment 2. Varieties employed were Bright Yellow in the experiment 1 and Hicks in the experiment 2. Plants were exposed to successive 8 treatments in the experiment 1, and similarly 14 treatments in the experiment 2. Then their growth were determined and aliquot of plants in each plot was transferred to greenhouse and grown to bloom. Stem length was increased with temperature, but its tenency was reduced at the temperatures higher than 43°C in the experiment 1, whereas in the experiment 2, it was decreased with temperature higher than 48°C, especially at 58°C it was seriously reduced. Emergence of leaves during treatments was reduced with increasing temperatures in any plot higher than 48°C, especially at 58°C plot. Changes in expansion of leaf area with time was increased most rapidly at the temperature of 33°C and declined at both higher and lower temperatures than this during experiment 1, whereas it was reduced proportionally with increasing temperatures in the experiment 2. There were apparent differences in the areas between upper and lower leaves. The area of upper leaves exposed to 33°C was the largest and reduced proportionally with temperature apart from 33°C, but thore exposed to high temperatures were larger than untreted control. On the contrary, the area of lower leaves exposed to high temperatures was reduced with increasing temperatures than untreated control plants except for 33°C plot. Dry matter of plants rose up to 33°C and then fell with increasing temperatures, but those exposed were larger than untreated plants except for 48°C. Apparent difference was observed in the dry matter distribution between stems and leaves. The portion of stem was increased and that of leaf reduced with temperature during exposures. Dry matter of leaves rose to maximum at 33°C and fell with increasing temperatures in the upper and middle leaves, but those exposed to high temperatures were larger than untreated plants except for 48°C in the middle ones. On the contrary, they were reduced with temperature in the lower leaves. Leaf area of the upper at the flowering stage rose to maximum at 43°C then fell again and that of the middle rose to maximum at 38°C and then fell with increasing temperatures but those exposed were larger than that of untreated plants except for 48°C in the middle leaf. Whereas that of the lower leaf reduced with increasing temperatures except for 33°C during experiment 1. On the other hand, in the experiment 2, leaf area was reduced in the lower leaves and increased in the upper at exposed plants as compared with untreated plants. But as compared with in each exposed plot, the leaf area was reduced by higher temperatures. The largest leaf was relatively in the upper position in the exposed plants as compared with untreated control plants. Serious injury was showed by a single or double exposures to 58°C in the experiment 2.