Vergara - 1976 - Physiological and morphological adaptability of ri

RESPONSE To DEEP “turn STRESS 317
Another important point is the fact that a source of energy or nutrients are essential for both
elongation and tolerance.
Therefore. from the physiological point of view. there is no conflict between the needs of the
two conditions.
‘Ne must try to breed varieties which are capable of vigorous photosynthesis and efficient
translocatitm of assimilates to the “sinks.” This of course is a general principle in the breeding
ofhigh-yield varieties and is not specific to floating rice.
Ilowever. a variety which has vigorous photosynthetic activity and abundant carbohydrate
reserve does not necessarily mean that it is suitable tor floating rice.
Some other factors must also be indispensable for quick elongation. For instance. rapid
production of growth hormone Under submergence.
lisrgui-u: Dr. lshiiuka, l completely’ agree with you on your discussion of temperature. l
wanted to fmd out what the water temperature is to study this factor. but when I was looking
for it we did not have anything. We really have to get more data on water temperature so that
we could run some physiological studies here. But as you pointed out we have a lot of things to
look into. Very few physiological studies have been done on floating rice.
On the source of energy. I really think the starch content of the eulm would be very important.
Again we do not know whether the floating-rice plant is like the traditional rice varieties
which accumulate a lot of carbohydrate before flowering so that even when they lodge they still
produce a certain yield. Perhaps the floating-rice varieties will be like this. Dr. Jackson and I
will be sampling our plots nest month. precisely to detemiine also the amount of carbohydrates
in the culm.
INOUE: Are you going to conduct any experiments on floating rices in the IRRI phytotron‘?
lkigara: I have no such plan at the moment. Temperature is not a limiting factor in the
culture of floating rice.
NISHnZ-tsta: How about the temperature distribution between different water depths. especially
in the case of very deep flood‘? Does the turbidity decrease the water temperature at the
bottom? ls there any problem of low temperature for the root?
Vergara: I am not aware of any data that show temperature profile in a deep water rice area
I do not believe that there is a problem of low temperature at the root zone.
Inous: ‘What do you mean by water temperature?
Veigara: This is the temperature of the water around the growing parts of the rice plant.
specifically the growing shoot and young intemodes. Water temperature at this level will affect
the rate of internode elongation.
htlomnrm: The physiologically significant temperature is probably the 24-hour average.
which is not likely to vary much with depth in the top l.-"2 m of water. So the profile is probably
less important than the trend of mean temperature in time (Dr. Ucliijimafs paper deals with
this point).
JACKSON: Were all of the rice varieties mentioned in your review floating varieties. especially
the Japanese work and your work with Peta on submergence?
lbw-gum: The varieties used in submergence studies were non-floating. The varieties used to
test the ability to elongate and the rate of elongation were the floating types.
JACKSON: l wish to comment on Dr. Okas point that the breeding and development of dwarf
rices tolerant to deep water is not emphasized in the paper. though the paper is a critical review
on deep water rice. Breeding research involving crosses betwen semi-dwarf and floating varieties
is well undervray‘ to transfer the improved plant type into dcp-yvatcr tolerant forms. This
includes characteristics such as erect and dark-green leaves. heavy tillering. and short height
(under shallow" water). A few such prototypes have already been developed which can survive
water depths up to 180 cm. Yield trials both in experiment stations and thrmefs fields indicate
that the new type is superior to the indigenous varieties. lt is anticipated that tiiture work on the
physiology of floating rice will also involve studies of these new semi-dwarf forms.
.-'\. TAMARA: Which roots- are more important in absorbing nutrient. those in the soil or in the
water’? Can you suggest a good method to apply fertilizer?
l "er-gum: No studies were made to show which roots are more important. Unless we know
this. the method of applying fertilizer for plant growth at the later stage wisuld be purely speculalive.
.-‘\ study of the nutrient uptake of the floating rices is sorely needed.
T. YOSIIIDAI It is quite interesting to me that adventitious roots are capable of absorbing
nutrients from water. How much can they absorb‘? And what is the ratio of nutrients absorbed