Vergara - 1976 - Physiological and morphological adaptability of ri

TENIPERATIIRE AND VEGETATIVE GROWTH 16?
generally showed greater tolerance than varieties from the southern Llnited
States; short-grain varieties were more tolerant than long-grain ones; no definite
relation was obtained with maturity" groups, except that none of late varieties
was equal in length to Caloro, which was the most tolerant. None of varieties
from Japan and other higher latitude countries was significantly superior to
Caloro, but many were considerably poorer.
Tanaka and Yainaguchi (1969) studied the effect of temperature on the early
growth of seedlings. The growth rate increased with increasing temperature over
a range from 20° to 30°C. However, the growth efficiency‘ (defined as the ratio of
produced dry matter to the sum of produced dry matter and respiratory consumption)
of rice seedlings germinated in the dark was constant over the same
temperature range. The growth efficiency of maize seedlings was also nearly
constant from 20° to 35°C; however, it decreased at 15°C and 40°C (perhaps
suggesting that the same effect occurs in rice seedlings).
Sasaki and his coworkers studied the relationship between germination at
low temperature and subsequent early growth of rice seedlings. Correlations
between germination coefficient and plant height, leaf length, dry weight. and
lcaf number at an early stage of growth were statistically highly significant
(Sasaki, 1968b). Positive correlation was also obtained between germination at
low temperature and root development at an early stage at low temperature
(Sasaki and Yamazaki. 1970); and between the germination and seedling
establishment (Sasaki and Yamazaki, 1971). These results show that varieties
which have high germinabilityt at low temperatures grow vigorously at the early
stage under low temperatures, and therefore the varieties are favorable to
seedling establishment with direct sowing on cool lowland fields.
SEEDLING ESTABLISHMENT IN TRANSPLANTING
Rooting
According to Yatsuytanagi (1960), the critical average air temperature for
transplanting is l5.0°-l5.5°C for rice seedlings reared in lowland nursery beds,
l4.0°—14.5°C for seedlings from semi-irrigated beds, and 13.0°-l3.5°C for
seedlings from upland beds. The transplanting period has been advanced about
20-30 day's by applying protected upland nursery beds in northem parts of
Japan. This difference in temperature sensitivity among seedlings grown
differently is considered to be due to the difference in seedling vigor (Yatsuyjanagi.
1960). For one thing, upland nursery seedlings have higher starch and protein
content. and thus higher rooting ability. than lotvland seedlings (Airni and
Nakayjama. 1957; Yarnada and Ola. 1957a. 1957b; Ota and Yarnada; 1958).
The rooting of rice seedlings occurs favorably over a range from 19° to 33°C
vrith an optimum at 25°—28°C; it is severely inhibited by temperature below
16°C and above 35°C (Nagai and Matsushita. I963‘. Matsushima et a1; 1968a".
Chamura and I-lonma, 1973). Root number also notably decreased at 9° and
13°C (Chamura and I-lonma. 1973). Root decay occurred increasingfv with
rising water temperature (Ueki. 1960; Matsushima et a1, 1968b).