Yoshida - 1981 - Fundamentals of Rice Crop Science

RICE PLANT CHARACTERS IN RELATION TO YIELDING ABILITY 223
growth before reproductive growth starts, provided there is no interruption. Thus,
the total growth duration of early maturing varieties is about 90 days. Directseeding
appears essential for a 90-day variety to have sufficient vegetative growth
before panicle initiation.
For transplanted rice with a total duration of 90 days, 20 days in the seedbed and
60 days for reproductive growth and ripening leave only 10 days for active
vegetative growth, which is not sufficient. About 100 days is the shortest duration
for achieving reasonably high yields with transplanted rice. In the comparison
above, the number of field days is 10 days shorter for a 100-day variety in
transplanted rice than for a 90-day variety in direct-seeded rice (Yoshida 1978).
Among the materials now available, IR747B2-6 is one of the best early maturing
lines in the tropics; it matures in 95–98 days (Table 6.4). IR36 matures in 105
days. Thus, attempts to shorten growth duration are approaching the limit for the
shortest possible growth duration with high yielding potential.
6.5. ASSOCIATION BETWEEN PLANT CHARACTERS
Conceptually, each plant character could be independent; factually, several plant
characters are often closely associated.
6.5.1. Foliar absorption coefficient and plant characters
The foliar absorption coefficient (k) is related to light penetration into a plant
canopy by equation 5.8:
I
In = –kF
I O
The foliar absorption coefficient is negatively correlated with specific leaf area and
the average leaf angle of the upper three leaves when measured from the horizontal
plane and weighted for the area of each leaf (Table 6.5).
Culm length is negatively correlated with the average leaf angle of the upper
three leaves. As a consequence, the culm length is positively correlated with the
Table 6.5. Correlation between foliar absorption coefficient
and some plant characteristics. a
Plant
characteristic
Correlation
coefficient
Culm length
+0.549**
Crop ht
+0.130
Number of culms -0.021
Mean area of single leaf
-0.244
Specific leaf area
-0.544**
Leaf angle
Leaf angle × specific leaf area
-0.539**
-0.717**
a Hayashi and Ito (1962).