Yoshida - 1981 - Fundamentals of Rice Crop Science

RICE PLANT CHARACTERS IN RELATION TO YIELDING ABILITY 215
grain yield. But higher solar radiation can compensate for such detrimental
temperatures. When 28°C is substituted for t and solar radiation is held constant, a
74% yield reduction, compared with the maximum yield achieved at a daily mean
temperature of 21.5°C, is obtained. Equation 6.1 was obtained by statistical
analysis. Hence, an extrapolation of variables beyond the range of the collected
data should not be allowed. Yet, the equation suggests that high temperature in the
tropics could be an important barrier to achieving high yields.
Later work at the International Rice Research Institute (IRRI) demonstrated
that high temperature per se in tropical monsoon Asia is not a barrier to increased
rice production up to 5–6 t/ha in the wet season and 9–10 t/ha in the dry. It was the
variety that hampered attempts to increase rice yields in experimental fields. High
temperature may be an important factor when the maximum potential yields in the
tropics and temperate region are compared.
6.2. NEW TROPICAL HIGH YIELDING VARIETIES
Emphasis was placed on improving japonica rices in Taiwan when it was under
Japanese control and ponlai rices were produced. After World War II the
improvement of native indica rices was started (Huang et al 1972).
In 1949, Dee-geo-woo-gen, a semidwarf indica that tillers profusely, was
crossed with Tsai-yuan-chung, a tall, disease-resistant variety. Taichung Native 1
(TN1) was selected from this cross and released in 1956. TN1 responds to high
levels of nitrogen. The yielding potential of TN1 is similar to that of ponlai rices. It
produces 6 t/ha, on the average, with the record yield of 8.1 t/ha. Thus, TN1 is
6.1. Effect of levels of nitrogen on the grain yield of indica rice varieties in dry (left) and wet (right)
seasons, IRRI (De Datta et al 1968).