Yoshida - 1981 - Fundamentals of Rice Crop Science

226 FUNDAMENTALS OF RICE CROP SCIENCE
6.8. Relation between growth duration
and plant height (Tanaka et al 1966).
6.6. CHANGES IN MORPHOLOGICAL CHARACTERS OF RICE
VARIETIES
The morphological character that has contributed most to high yields is a short,
stiff culm that gives lodging resistance (Shigemura 1966, Chandler 1968).
Changes in the morphological characters of rice varieties that became commercially
available between 1905 and 1962 in Hokkaido, Japan, indicate that varieties
have been selected for shorter plant height, higher tillering capacity, and more
erect leaves (Fig. 6.9). Increasing LAI is associated with higher tillering capacity.
Shorter plant height (lodging resistance) and higher tillering capacity (increasing
LAI) would have contributed more to increased yield and nitrogen response than a
smaller foliar absorption coefficient. The crop photosynthesis model suggests that
leaf angle (foliar absorption coefficient) is not too important up to a LAI of 3–4
(Monteith 1965, Duncan 1971, van Keulen 1975). A similar trend is also observed
for rice varieties in southern Japan (Ito and Hayashi 1969).
Historically, the selection must have been based on selection for yield with
liberal use of nitrogen fertilizers and improved cultural practices such as close
spacing. However, the outcome of this selection agrees with the present knowledge
of the physiological aspects of high yields in transplanted rice.
6.7. MODIFICATIONS OF VARIETAL TRAITS FOR SUBNORMAL
CONDITIONS
Under subnormal management conditions, high yielding varieties may or may not
be good yielders. The recent recognition of diverse environments in rice-growing
regions indicates the need for a better understanding of the benefits and disadvantages
of contrasting plant characters (Yoshida 1977b, 1978). With such informa-