Vergara - 1976 - Physiological and morphological adaptability of ri

STERILE-TTPE COOL INJURY IN PADDY RICE PLANTS 299
2. The correlation between tolerance to sterility and tolerance to cool temperature at another
stage is not high among the Hokkaido varieties.
ORA: How about the difference among varieties‘? For instance, do you have a variety; that
can resist I7"C temperature at the most critical stage? And to what degree?
Surake: We have varieties that can resist l7°C. Sterility begins to increase when the temperature
at the most critical stage drops to l5"—l7"C in cool-tolerant varieties and to l'.l"—l9“C in
cool susceptible ones.
EVANS." Now‘ that the stage at which cold-injury is induced has been so well defined. has the
Hokkaido phjrtotron been used to seleirt genotypes more resistant to such injury for plant
breeding programs?
Sara/re." We have used our phytotrtvn mainly to make physiological experiments. Man): other
growth cabinets at Kamilmytra Agricultural Experiment Station in Hokkaido and at Fujisaka
Experiment Station in the Tnhoku district have been used to select gcntnyjacs that are more
resistant to cool injury.
BUYER: As an agronomic technique usable by farmers. can the cold sterility problem be
tivercorne by hand-pollination from a few plants grown under warmer temperatures’?
Samke: Aetiirity‘ of the rice pollen is rapidly‘ lost after shedding. Pollen grains maintain
their activity‘ for only a few minutes alter shedding. Because of this, it is almost impossible to
use your idea as an agronomic technique.
ISHIZLFKAI But l think this research is very fundamental. So all of you have the question
how to apply his result in practical agriculture. That is an inlportant point. This is not only for
cold injury but also for drought and deep-water stress. So later in the session l wish to again
raise questions on this point and ask for your discussion.
IEUQAIIASIII: I have been of the impression that heavily fertilized rice is more liable to cool
injury. Now you state that the chemical component has nothing to do with cold injury. Do l
understand that fertilizer has nothing to do with the destructive type of cold injury"!
Sumke.‘ It is well known that heavily nitrogen-fertilized rice is mofl: liable to cool injury.
What I mentioned is that the decreases o1‘ some constituents in anthers, detected at ‘P5
day's after cooling. show not the catlses but the effects of cool injury.
TAKAHASHlI If We apply lots of fcnilizcr. this destructive type of injury is also related. So l
think that some component is related to this problem. For example, it was quite a long time ago
when this type of cold damage was studied at the National Institute of Agricultural Sciences.
They found that sugar content was related to longevity‘ of pollen and was related to cold injury.
Have you examined the sugar content. for example?
A. 'l'A.NAiL-\: Dr. Satake has mentioned in his summzuy that initial injury of coolness in
anther cells is the disturbance of carbohydrate metabolism. ls this your opinion‘?
Tnl-tiAHhSHti The author has stated that it is not the cause but a result. though the physiological
component should have nothing to do with the cool injury‘. lsn‘t that correct?
Sarake: Not quite. I think that some physiological components are closely related to cool
injury‘. What I said was that the decrease of nitrogen content in cooled anther detected 4—5
days after cooling is not the cause but a result of cool injury. The increase of sucrose in cooled
anther during cooling period may be a cause for cool injury.
Psicitlux); Would you explain further how sugar accumulation could lead to the breakage of
intertapetal walls?
Sula/re." Abnomial accumulation of sugar and of other substances of low molecular height
in tapetal cells raises the osmotic pressure and induces the breakage ol‘ walls. This is only a
working hypothesis.
NIX: I have a comment. The temperatures at which cold damage occurs appear to coincide
very closely with the threshold temperatures for cell division in a given cultivar (l5“—l7"C).
Kltlhere cell division ceases but the supply of carbon compounds continues, one would expect
an increase in osmotic concentration in stirrounding cells and possible physical and biochemical
damage. One could regard the effect as an extreme ease of sink-source imbalance.
AHN: ls there any relationship between sterile-type and delayed-type cool tolerance‘? l think
there may be. For example. in Korea. Tongil (an indica-japonica hybrid) was not only very
much delayed in heading but also affected in anther opening under cool temperature.
Satake. lt is true that some varieties are tolerant to both types. and some varieties are susceptible
to both types. Generally; speaking. the correlation between the tolerance l0 sterile-type