Vergara - 1976 - Physiological and morphological adaptability of ri

184 (TLlb-LYIE AND rucs
DISCUSSION
TANAKA (Chairman): Dr. Nishiyama presented a comprehensive compilation of available
data on the critical-low. optimum. and critical-high temperatures on various morphological
and physiological processes of the rice plant. and discussed the existence of thermal anomalies
around l5. 30. and 45°C.
From this reviev/ it can be said that the data in some literature are in agreement but those in
others are not. This disagreement arises because the data cited are those obtained from experiments
using different varieties and different methods: there are varietal differences in temperature
response. old experiments were not so well controlled as more recent ones. and the experimental
conditions of one experiment are different from those of others although the treatment
temperature is the same. Moreover. data on some aspects are missing. Thus, it is necessary to
conduct more experiments to have a complete set of reliable data.
I would like to mention that the effect of temperature on morphological processes can be
classified into two categories, recoverable and irrecoverable. For example. by a low-temperalure
treatment (below l5“"C) for a few days during tillering stage the tillcring is stopped; but if
the temperature goes up later. the tiller number continues to increase rapidly and may reach a
normal level depending upon the condition (the recoverable etfect). However. by the same treatment
during the panicle-primordium development stage the sexual organs are damaged irreversibly
and the fertility of flowers decreases remarkably regardless of the condition during
later growth stages (the irrecoverablc effect]. A lovr-temperature treatment during the particleprimordia
development stage exhibits a recoverable efiect when the treatment is mild. but an
irrecoverable etfeet when it is more severe than critical. lt is important to identify these two
categories while studying the effect of environmental conditions on the grain yield.
Dr. Nishiy-"ama concluded: "Agricultural problems are highly complex. Scrupulous caution
is needed for analyses of those problems." It is extremely’ difficult to identify the temperature
effect on a specific physiological process. such as respiration. nutrient absorption. translocation,
ctc.. because these phenomena interact. and a temperature treatment effects not only the process
in question but also related processes occurring simultaneously-i Such interactions are much
more complicated in morphological processes. such as the differentiation and growth of leaves.
tillers, roots. particles. ctc.. than in physiological processes. It is essential to make critical efforts
to identify the direct effect of temperature on a process. isolating it from indirect effects expressed
through interacting processes. However, if one goes too far in this direction. studies may
become too fundamental and so have no immediate agricultural implications.
Dr. Nishiyama mentioned that the temperature response of the rice plant can be shified by
breeding as well as by cultural improvement. We still don't know exactly how far was can go
toward this. Solution of such problems will make a real contribution to rice production in areas
where temperature is a problem.
After realizing these problems. agricultural scientists are requested to think about methods to
utilize the excellent phytotron IRRI now has. to solve our problems with maximum clficiency.
Phytotrons are expensive. but give precise controls of temperature. light. humidity. etc. Given
a good phytotron. the challenge is to determine how to use it for improvement of crop production.
Pmmo: In your sununary; the favorable temperature range for physiological properties ot‘
rice plants is from l5"‘—l8°C to 30°~33°C. Does this mean that the range is from l5‘ to 33"‘C.
Please clarify this range.
Nrshrlvama." The paper I presented is a very comprehensive summary through the different
growth stages of rice plants. So. the temperatures are only roughly estimated. It cannot be
identified so clearly as l5" or 33"C. This temperature range is favorable in a physiological sense.
That is, the range is between two critical temperatures. For practical purposes. however. this is
not really the most favorable. The definition must be that the favorable temperature is one
which gives the maximum activity cover a definite level. In this sense, the tavorable temperature
range is usually‘ higher in many physiological phenomena; that is. liom 20°—23°C to 35“—38°C.
IviONTI-ZFFH: The data in Fig. 2 and 3 can be replotted to show that the rclevsant rate is a
simple linear function of temperature. The slope of this relation gives a temperature requirement
in day-degrees. cg. the requirement for 3-cm plumule elongation is 90 day"r‘C above 12°C.