Abstract
Varietal responses of heading date, number of main culm leaves and leaf emergence interval have been investigated with 48 paddy rice cultivars differing date of maturity under five different levels of temperature using semi-open air controlling cabinets. Early maturing varieties tend to be more sensitive to temperature in heading and late ones show less sensitivety. But the relative order of heading date among varieties is rather stable and little disturbed by temperature treatments. Varietal responses to temperature in heading are explained in terms of number of main culm leaves and leaf emergence intervals in the following way. 1) When early maturing varieties are grown urLder warm condition, the leaf extension is accelerated and leaf emergcrence intervals are remarkably shortened. Also number of main culm leaves decreases under high temperature. They have large variability in heading: date under different air temperatures. 2) The situation is different in late maturing varieties. When they are grown under warm environment, the leaf emergence intervals are shortened on one hand, but numberof main culm leaves increases on the other hand. On the contrary late maturing varieties, grown under cool enviromrrent are slow in extending leaves but develop smaller number of leaves. In consequence late maturing varietis are less variable in heading date under various temperature conditions.
