Yoshida - 1981 - Fundamentals of Rice Crop Science

56 FUNDAMENTALS OF RICE CROP SCIENCE
1.46. A spikelet of rice
(adapted from Nagai
1962). g = sterile lemmas,
g’ = rudimentary
glume. R = rachilla,
I = lemma, p = palea.
lo= lodicule, o= ovary,
st = stigma, sty= style,
a=anther, f=filament.
1.10.2. Heading
After the flag leaf emerges about 18 days before heading, the panicle grows fast
and moves upward in the flag leaf sheath as the internodes elongate. About 6 days
before heading, the flag leaf sheath thickens — an indication that a panicle is
enclosed. The 6 days are called the booting stage.
Elongation of the second internode from the top is completed 1 or 2 days before
heading. Then the topmost internode elongates rapidly and pushes up the panicle.
As a consequence, the panicle is exserted from the flag leaf sheath. Heading means
panicle exsertion. In general, panicle exsertion is fast and complete in japonica
rices, but slow and incomplete in some indica rices. Low temperatures aggravate
poor panicle exsertion.
Within a plant, some tillers usually head earlier than the main shoot. The date of
heading differs not only within a plant but also among plants in the same field. It
usually takes 10–14 days for all the plants in a field to complete heading. For
convenience, heading date is defined as the time when 50% of the panicles have
exserted.
1.10.3. Anthesis (flowering)
Anthesis refers to a series of events between the opening and closing of the
spikelet, lasting about 1–2.5 hours. At the beginning of anthesis, tip portions of
the lemma and palea begin to open, filaments elongate, and anthers begin to exsert
from the lemma and palea. As the spikelet opens wider, the tip of the stigma may
become visible. The filaments elongate further to bring the anthers out of the
lemma and palea. The spikelet then closes leaving the anthers outside.
Anther dehiscence usually occurs just before or when the lemma and palea open;
consequently, many pollen grains fall onto the stigma. For this reason, rice is a
self-pollinated plant.