Th~.
effects
of
air
temperature
and
light
on
the
grain
filling
of
an
indica
(IR20)
and
ajaponica
flce
(FuJlsaka
5)
was
studied
in
artificially
lighted
cabinets.
Within
the
daily
mean
temperature
range
of
16°
to
28°C,
the
higher
the
temperature,
the
faster
the
grains
filled
and
matured.
At
28°C,
the
upper
grains
of
IR20
rice
took
13
days
to
reach
the
maximum
weight,
whereas
those
of
Fujisaka
5
took
18
days.
The
optimum
daily
mean
temperature
range
to
achieve
maximum
weight
per
grain
was
19°
to
25°C
for
IR20
and
16°
to
22°C
for
Fujisaka
5.
Apparently,
IR20
rice
is
better
adapted
to
higher
temperatures
during
the
ripening
period
than
is
Fujisaka
5
rice.
More
chalky
grains
occurred
when
the
temperature
was
above
or
below
the
optimum
range.
Both
day
and
night
temperatures
affected
grain
weight
and
grain
quality.
The
daily
mean
temperature
was
found
to
be
the
most
meaningful
expression
for
describing
the
effect
of
temperature
on
grain
filling.
Low
light
intensity
appeared
to
cause
a
slight
delay
in
the
grain
filling
of
the
whole
panicle
and
a
reduction
in
the
percentage
of
filled
grains
on
the
lower
branches.
A
combination
of
high
light
intensity
and
low
temperature
gave
the
best
ripen-
ing
grade
(grain
weight
X
percent
filled
grains).