Yoshida - 1981 - Fundamentals of Rice Crop Science

PHYSIOLOGICAL ANALYSIS OF RICE YIELD 251
One possibility suggested by the CO 2 enrichment is to increase photosynthesis
during panicle development before flowering. Increased photosynthesis may be
achieved by increasing photosynthetic efficiency or by extending the time for
panicle growth. A group of physiologists has been trying to eliminate photorespiration
in C-3 plant species either through chemicals or by genetic manipulation;
the elimination of photorespiration is believed to increase the net photosynthesis of
C-3 species by about 50% (Zelitch 1979).
Relatively small differences exist in the length of the period from the initiation
of panicle primordia to heading under normal crop conditions. In general, total
growth duration and the length of the period from panicle initiation to heading are
positively correlated. Thus, an early maturing rice variety has a relatively short
time for panicle growth (Akimoto and Togari 1939). Because longer growth
duration is not generally desirable, can the period of panicle growth be extended
independently of the whole growth duration? Partitioning of assimilates between
developing panicles, leaves, culms, and storage is probably under hormonal
control. The distribution of a greater portion of assimilates into developing
panicles may produce larger panicles. The flag leaf of most improved rice varieties
is relatively small compared with the second or third leaves. Possibly this results
from competition with the developing panicle. Attempts to understand and control
the mechanism for partitioning assimilates merits much more attention.