Vergara - 1976 - Physiological and morphological adaptability of ri

'l'El\‘lPERA'l'LlRE AND LIGHT. REPRODUCTTVE GROVWTH AND RLPENING T99
0 9
O8 —
0 7 —
O6 —
Heading
Q 1 I | l l | | I | |
-40 _2o O +20 + 4O
Stage from heouing tnrrvetdcys)
9. Change in multiple correlation coefiicient of ripening
gade ‘with grouth stage. Model: Modified type IV
(ltlj) - 11,715‘ l b_TS » b.~TS - lnTS I b,1" It bu?
+ b1T+ In T + c
where T = l0‘ exp (~ 7.000 {I l 273). 2)
S = s i 4.5
t and s: mean values for 20 days of temperature and
sunshine hours.
The trough between two peaks is cqual to heading timc. The fact that thc
effect of climate at heading time is relatively small is interesting. This may be
partially" attributed to small variance of climatic factors at heading time. The
standard deviation of temperature throughout the whole growing stage becomes
minimal near heading time (sec Fig. 2). This tendency was not observed xvhen
the data were divided into several groups ‘with similar temperature conditions.
However the declines in multiple correlation coefficient (R) at heading were still
observed in each of the groups.
Thus. it appears that this phenomenon is not necessarily caused by the small
variance of temperature.
Shibata ct al. (1970) found that the occurrence of sterile paddy by low" temperature
treatment was more serious at the spikelet differentiation stage than at
heading time. It was also pointed out that when the period of low temperature
treatment was not so long, the rice plant might escape chill injury b)" delaying
the heading time.
lt was difficult to explain, however, why the decline in R [sensitivity to climate)
at heading was observed even in warm regions.
Functional relationships between ripening grade and temperature
When sunshine hour (s) in eq. (2) is fixed. the regression curve of the ripening
grade on temperature at four stages is shown in Fig. l0. From this. it is found
that temperature curves of ripening grade differ with growth stages.
At l- 20] stage. which is one of two stages xvith higher R value. the optimum
temperature for ripening grade is about 23°C (Fig. 10A). The characteristic of