Vergara - 1976 - Physiological and morphological adaptability of ri

160 CLIh-LATE AND RICE
The effect of temperature on rice production is very divergent and complex.
Temperature affects rice plants both directly and indirectly-g for example. through
outbreaks of diseases or changes in soil conditions. The effect of temperature
differs among different physiological properties and among different organs of
rice plants. Developmental age. variety". cultivation methods. and environmental
conditions are also factors which influence the relation between temperature
and rice production. Application of sharp scientific scalpels to this complexity
will contribute to improvements in rice production.
GERMINATION
Lower and higher limits of germination temperature
Exact estimation of the lower limit for gennination is rather difficult. Gennination
proceeds very slo\vly under low temperatures. and the seeds are likely to
rot before germination. The temperature at which any seeds can germinate
seems to be near 0°C (for riee plants of cool-tolerant varieties). Himeda (1973)
reported that some varieties can germinate at 5°C (0 to 27 percent for seven
varieties). The author has observed the germination of seeds at 2°-5°C. though
the seedlings could not grow at this temperature.
Reported values for the lowest temperatures of gennination are: lower than
10°C (Chaudhary and Ghildyal. 1969). lower than 9°C (Aleshin and Aprod,
1960). lower than 8°C (between 8° and 13°C for other less cruel-tolerant varieties)
(Lee and Taguehi, 1969), lower than 12°C (Livingston and Haasis, 1933). lovrer
than 11°C for varieties from Japan, and lower than 13°C for those from tropical
areas (Oka, 1954).
Tropical varieties show‘. in general, higher minimum temperatures than temperate
varieties (Oka. 1954). and indiea varieties show. in general. higher minimum
temperatures than japoniea varieties (Matsuda. 1930'. Pan. 1936'. Wada,
1949; Ormrod and Bunter, 1961a). Oka (1954) reported that insular varieties
showed lower minimum temperatures than continental varieties.
Among Japanese varieties. Nakamura (1938) reported that germination at
low temperatures tvas the best in early ones. and decreased in the order ofmiddle
ones and late ones; on the other hand, Sasaki (1968a) reported that germination
ability was not highly correlated with grmvth duration; upland rice was usually
better than ltm-"land rice (Onodera, 1934: Iiarashima. 1937; Nakamura, 1938);
and glutinous varieties were better than ordinary ones (l-larashima. 1937; Nakamura.
1938). On the other hand. indiea varieties did not seem to shtiw differences
among different maturity periods (Pan, 1936; Ormrod and Bunter.
1961b).
Reported values for the upper limit of germination temperature for rice
plants are: higher than 40°C (Umino. 1944). higher than 42°C (Livingston and
Haasis. 1933) and 43°C (Chaudhary and Ghildyal. 1969). According to Owen's
review’ (1971). “There is agreement that the maximum temperature for germination
is in the region of 40°—45°C."