Vergara - 1976 - Physiological and morphological adaptability of ri

PHYSIOLOGICAL AND IVIORPHOLOGILTAL AD.i\P’l';-\Bll.l'l"i'
ll/IONTEITIIZ We are still a long way from understanding the first-order effects of
weather on crop growth without tvorrying about sccond- or third-order effects. I suggest
that two of the effects mentioned in your paper are very minor. First. wind-tunnel
studies have shown that the fluttering of a leaf makes very little ditTerence in the boundary-layer
resistance because the laminar layer remains attached. Typically’. the resistance
may decrease by 10%», and the consequent increase in photosynthesis rate is
unlikely to exceed 1%. Second. the main spectral effect of water is to absorb infrared
radiation. leaving the visible spectrum practically unchanged. I doubt very much
whether small changes in the balance of blue and red light in different seasons are
physiologically significant. either for photosynthesis or for photomorphogenesis.
Veiganzr: As l said earlier. l reviewed whatever papers were published on adaptability‘.
I am sure your comments will be an important addition at the end of this paper.
JACKSON: Please comment on the need for photoperiod sensitivity as an advantage
for upland and rainfed rice.
lergara: Our tests on the photoperiod response of upland varieties showed that
majority’ of the upland varieties are insensitive to photoperiod. Upland varieties are
generally planted when the day lengths are lung — hence the need for insensitivity’ if
the variety is expected to flower and mature in the shortest time.
In our tests we came across four upland varieties from the northern part of Thailand.
The varieties needed in this area must have long growth-duration because of the
scanty and bimodal distribution of the rainfall. The plants are sovm in April-May and
harvested in September-October. To have a long grovrthduration variety, one has to
use the photoperiodsensitive one where the growing periods can be extended. l am glad
you ask this question. Dr. Takahashi also uants this fact to be known to breeders
developing upland rice varieties.
Titimlirtslll: In the north and northeast of Thailand. substantial rain (enough for
transplanting) comes as latc as September in some years. Niay I have your recommendation
as to what variety should be grown in such cases? (This question was asked in
relation to that of Jackson).
Vergara: Of all the upland varieties that we tested. ue came up with four that are
sensitive to photoperiod. and they happen to be from the northern pan of Thailand.
So they are using photoperiod-sensitive varieties. This is the collection of Dr. Oka,
made in northern Thailand. and we are trying to explain why they use these varieties.
llttinnitstil: The farmers want to plant when water is available. which may be in May
or June or July.
Vergara: ‘When do you harvest‘?
Tixl-L-ttmstil: November.
Vergara: It" it is November and you plant in April or lytay’. you nccd long-duration
varieties which have to be photoperiod sensitive because the longest one that we could
find that is insensitive is about 140 days. If you go to 160 day's or I80 days you have to
use the photoperiod-scnsitivc varieties. We cannot have a variety" that is insensitive
and has a long growth duration. I am glad you told me about this early planting. Now
we can explain why the upland varieties there are sensitive to photoperiod.
ORA.‘ What are your criteria for “wide adaptability”? There might be two aspects.
one depending on particular outer conditions (specific adaptability) and the other dealing
with the overall response to many and unspecified conditions (general adaptability).
This classification is operational. But I think that these should be distinguished in the
present discussion. ‘What evidence do you have in mind on the role of genetic heterogeneity
in increasing “adaptability”?
Vergara: l think that is why at the beginning I tried to give my definitions of wide
adaptability and specific adaptability: Now on the role of genetic heterogeneity, I am