Vergara - 1976 - Physiological and morphological adaptability of ri

188 CLIMATE AND RICE
reactions other than the biological clock. Therefore, the combined effect of
temperature and light on the plant growth is not simple.
The reproductive growth of a rice plant goes on for a lengthy period of about
6O day's from initiation of paniele formation to grain maturity. The rice plant
during this period carries on morphological differentiation as well as increasing
dry matter. Grain yield is essentially determined through two processes. spikelet
formation before heading and grain ripening after heading. Consequently‘.
farmers and researchers have given special attention to climatic conditions
during the reproductive growth period.
ln this report. the functional relationship between climatic factors and reproductive
growth of rice will be discussed, and several types of mathematical
models expressing the complex effects of temperature and light on grain _vie1d
and its components Will be proposed.
ANALYSIS
PROCESS
Collection and expression of data
The data on yield, its components. and meteorological factors WCIC obtained
from the reports of Statistics and Survey Department in 1961-1971. All of the
data on yield and its components in these reports represent average values from
about 200 fanner fields in individual prefectures every year. The data used herein
cover the 23 prefectures which comprise the major rice-production area in
Japan. These prefectures range from coo] region (Ielokkaido) to WHTITI region
(Kyushu). The total number of samples was about 200. The items of rice plant
data used for analysis were the heading time. the number of panicles per
square meter (11). the number of spikelets per square meter (1)), and yield (L).
The yield represents the kernel weight per square meter. Table l shows that the
highest correlation was between yield and ripening grade‘. the second highest
was between yield and number of spikelets per square meter. However, there
was no significant correlation bCWVCCIl these yield components.
Temperature and light environments were expressed by the daily mean air
temperature (t) and the daily mean sunshine hours (s). Expressing light environ-
Table 1. Simple Correlation coefficients between individual yield
components (1961-71. 23 prefectures in Japan. M205).
Panicles Spilcelets Yield
Y, YJY. Y; YJY; Y;
Panlcles Y, 4166 0 86 -0.12 0.46
YJY, -O 19 0.0? -0 05
Sprkeiets Y; -0.08 0.59
Ripening g. YJY; 0. ‘F6
(CV %) 146 7'2 ‘I15 134 169
‘(.2 number of panicles/ml.
Y1: number of spikeletslnv (included non-ripened spikelets)
Y3: kernel yield tglnr)
YJYt: number of sprkeletsipanlcle
Y)”; ripening grade (kernel weight/spikelel, mg].