Vergara - 1976 - Physiological and morphological adaptability of ri

168 CLINLATE AND RICE
Top growth
Top growth of rice plants after transplanting is, in general. linearly accelerated by
raising average temperature from approximately 18°C to 33°C (Ueki, 1966;
Place et al.. 1971'. Sato. 1972a; Chamura and Honma, 1973; Osada. Takahashi.
Dhammanuvong, Sasiprapa. and Guntharatom. 1973; Yoshida. 1973). Above
and below this range. the growth notably decreases. Water temperature is
much more significant than air temperature for early growth and development
of lowland rice (Matsushima et al., 1964b. 1966. 1968a. 1968b; Hoshino et a1..
1969). This is because the growing points of the plants are under ivater. The
effects of water temperature on the early growth of rice plants are basically the
same as those mentioned above (Matsushima et a1, 1964b, 1968b). Sato (l972a)
found that dry matter production was the largest under a day-night temperature
regime of 30°—25°C for Norin l7. and at 25°-20°C for 1R8; leaf area per plant
was the largest at 30°—25°C for both varieties; thus. the temperature of 35°—30°C
was overly high for the growth ofeither japonica or indica varieties.
Sasaki (1927) reported that the elongation of riee leaves increased with rising
temperature from 17° to 31°C; thence it tended to decrease and practically
ceased at 45°C. The lower limit of temperature for rice leaf elongation was
estimated at 7°—8°C (Sasaki. 1927). at 10°C (Aimi. 1965) and at 12°C (Tanaka
and Munakata, 1974). Oda and Honma (1963) reported that the velocity of leaf
emergence was greater at ivanner conditions. and this hastened heading accompanying
the decrease in leaf number.
Kaneda and Beachell (1974) surveyed the types of cold injury of rice plants in
more than 10 countries. For cold injuries at vegetative growth stages, failure in
germination and slow seedling growth were observed in almost all countries
surveyed; stunting and discoloration of leaves ivere reported in more than half
of them. Crennination and early seedling growth have been discussed earlier in
this review Seedling discoloration is commonly seen in indica varieties grown
under low temperatures. The discoloration is tisually various degrees of yellmving
of leaves; sometimes white specks on leaves and white bands on sheaths, or
whitening of entire leaves are observed. At tillering stage. the yellotving occurs
on lower leaves. Stunting occurs at tillering stage in boro crops. Yellowing of
leaves was observed also in japoniea varieties grown at 9° and 13°C (Chamura
and Honma. 1973).
Tillering
There is disagreement among reported data about the effect of temperature on
tillering. First, a number of researchers (Oka. 1955; lakahashi et al._ 1955;
llasegawa. 1959'. Nagai and Matsushita. 1963; Matsushima et a1. 1964b‘.
Kakizaki. 1965; Charnura and Honma, 1973; Yoshida. 1973) reported that
tillering increased with rising temperature in a range from approximately 15° to
33°C. Among them, Oka and Takahashi et a1. indicated that the tillering period
was shortened by the optimal temperatures for tillering differentiation. and
thence the final number oftillers decreased with rising temperature. Matsnshima