Yoshida - 1981 - Fundamentals of Rice Crop Science

50 FUNDAMENTALS OF RICE CROP SCIENCE
1.42. Female panicle with twin rachisbranches
on a neck node (Matsushima
1970).
branches on the panicle axis. An ample supply of nitrogen at the neck-node
differentiation may produce high percentages of female panicles. Thus, the formation
of female panicles indicates good growing conditions at the neck-node
differentiation.
When a panicle is carefully examined at maturity, many degenerated vestigial
organs can be recognized: spikelets, primary branches, secondary branches,
bracts, and the growing point (Fig. 1.43). These organs degenerate between
spikelet differentiation and the end of reduction division while differentiation
occurs during the preceding period, neck-node differentiation to spikelet differentiation
(see next section). The environmental conditions at each period have a
profound influence on organ differentiation and degeneration. The spikelet
number observed at maturity is the difference between the differentiated and the
degenerated.
1.9.2. Outline of panicle development before heading
The initiation of panicle primordium starts about 30 days before heading; it
corresponds to the time when the fourth leaf from the top begins to elongate.
Panicle development and growth start with the neck-node differentiation and
end when the pollen is fully matured. Table 1.13 shows the sequential steps of
panicle development. The total duration of panicle development varies with
variety and weather and ranges from 27 to 46 days. The duration of panicle
development is shorter in early-maturing varieties than in late-maturing varieties.
Under normal weather conditions and for medium growth duration varieties,
however, the total duration of panicle development is about 33 days. The results in
Table 1.13 were obtained from studies in japonica rice in Japan. Since there is no