Vergara - 1976 - Physiological and morphological adaptability of ri

RICE PRODUCTIVITY IN CLIMATIC REGIONS OF JAPAN 453
the number of tillers increases. the total number of leaves also increases at the
same pace, coupled with the growth of individual leaves. The tillers thus formed
also produce new secondary tillers with developing new leaves on them. The
secondary tillers produce tertiary tillers in the same way. Thus. the total leaf
area per plant increases exponentially up to the maximum-tiller-number stage.
about 40 days after transplanting in temperate regions.
After the maximum-tiller-number stage. some of the newly produced tillers
begin to die
ears, the differentiation of new leaves stops although the growth of some continues
until heading. Thus. the total leaf area or leaf-area index increases rapidly
for some time after the maximum-tillcr-numbcr stage. but the ratc of increase
becomes smaller and smaller until the plant attains its maximum leaf area at
around heading time. Leaf area rapidly decreases thereafter as the plant matures.
Temperature and leafarea development
When the average rate of leaf area increase during the first 6 weeks after transplanting
is compared in different locations. using the IBP field experiment data.
the rate is found to be most heavily dependent on the mean daily temperature
during the same period (Fig. l). In other words. at this young stage of exponential
growth, most of the difference in the rate of leaf area development is attributable
to the difference in mean temperature.
A similar conclusion has been reached by Kumura (I975) from the analysis
of the IBP seedling experiment. the sowing date experiment. Partial correlation
coefficients were ealculated between the relative growth rate of leaf
area. LRGR. and the mean temperature as well as solar radiation. for a 1-week
period. using the I96 data pooled for 4 years in five stations. A value as high
as (1.745. significant at the 0.1 "/0 level. was obtained as the partial correlation
coefficient between LRGR and temperature excluding the influence of radiation.
That between LRGR and radiation excluding the influence of temperature was
only 0.206. but still significant at the l % level. This indicates the far greater influence
of temperature as ivell as the relatively’ small influence of radiation on
leaf area development at a young stage of the plant.
As described earlier. the leaf area development at a young stage of the plant
is determined by the increase in number of tillers and the growth of individual
leaves. As to the relationship between leaf growth and climatic factors. Sasaki
H927) has shown that the growth in length of a rice leaf was most rapid at
31°C. To study“ the relationship between tillering and temperature. Matsushima
et al. (I966) grew rice seedlings for 3 weeks under different combinations of
air temperature and ivater temperature. Irrespective of the air temperature.
the number of tillers produced was most severely affected by water temperature
to which the growing point of the young plant was exposed. Under lower
xvater temperatures. tillers emerged from the lower nodes of the culm. while
under higher water temperatures they emerged from the middle and upper nodes,
because the tiller primordia at lower nodes became dormant under high water