Vergara - 1976 - Physiological and morphological adaptability of ri

1 l0 CLIMATE AND RICE
effective for developing yield stability and wide climatic adaptation. However, this technique
need not be restrictive to areas of long growing seasons nor is it restricted to availability of a
large number of locations. Yes. this is desirable, but not ahvays necessary".
How many of you conduct studies year after year in an effort to measure climatic response‘?
How ofien do you replicate these studies within a single year? Yes, date of seeding tests can
provide valuable information on climatic response. especiall_v in areas of restricted growing
period. A few weeks difference in planting date in many areas will provide a large difference in
climatic conditions at each stage of growth and development. Do we tiilly utilize this tool to
measure climatic response under field conditions?
An interesting point in Dr. Change presentation concerns specific adaptiveness within cultivars
having wide climatic adaptability. He stated: "Varietal improvement would simply involve
the incorporation of a specific type of tolerance or resistance into a widely adapted
genetic background; in other instances. the reintroduction of a specific photoperiod response or
of temperature response into a modified type with moderately tall plant stature. This may
appear as a reverse step in crop evolution, but a necessary one."
We used to call this "broadening our genetic base," an ambiguous temi meaning climatic
adaptability.
FMNKEL: Does Dr. Chang agree that there is a need for differentiation between adaptability:
to seasonal variation willim an ecological site and to variation between sites‘? If so, the need
arises for adaptedness to distinct ecological situations, rather than adaptability over a wide
range of environments. ln the short term. wide adaptability is desirable, but is it in the long
term?
Chang: l agree with you on this point. Whenever a grcatcr resolution is provided to a complex
trait. we can expect greater advances in genetic analysis or genetic improvement. In order to
have high production level at every site. specific adaptivcness is essential.
FlLaNI-LEL: Dr. Vergara used the word adaptability for almost anything related to adaptation.
Now here you spoke of specific adaptability, which to my mind is not a very useful tenn. I
would have thought this should be called adaptiveness. and there is a considerable difference
between adaptability‘ and adaptiveness. And I think our term adaptability is a regrettable one.
Chang: l agree that adaptability should refer to the ability to become adapted; adaptation.
the process of becoming adapted; and adaptiveness, a condition of being adapted.
GHILDYALZ Do the genes for grovflh duration you mentioned govern differences due to soilroot
temperatures or atmospheric temperatures? Both may vary considerably.
Chang: Yes, plant response to atmospheric temperature may differ from that to soil-root
temperature. though the two factors are somewhat interrelated. In those studies where air
temperatures were investigated, l do not recall any mention of soil-root temperatures.
CHANDLER: In your slides your drought resistant varieties (and genetic lines. too) were fairly
tall. Is there any genetic barrier to obtaining. through breeding, shoi1, heavy-tillering.
drought-resistant varieties‘?
Chang: In our first group of crosses. each including a tall drought-resistant Atiican upland
variety and a sernidwarf. we recovered mostly tall and rather low tillering progenies that can
withstand drought. The shoit-statured progenies were few in number, generally susceptible to
drought, and weak in growth. We hope to overcome this barrier by crossing these tall lines with
shorter. higher-tillering lines. On the other hand. we arc conscious of the root-to-shoot ratio. “H:
do not expect a rather small root system of rice cultivars to be able to support many tillers.
CHANDLER: Apparently that is a correlation between plant height and root length that is
hard to break?
Chang." l don‘t know whether we can break it sufficiently We can further reduce the plant
height and still retain most of the root features by continued crossing. so I don‘t believe we have
had a drastic restriction on gene recombination. We may find restriction on some of the genes.
but not on the full range of recombination
S. YOSHIDA: I think that is a real question we are asking ourselves.
Evans: In wheat. association between plant height and root length has been broken. hleirican
semidwarf varieties have deep roots. I think it is possible.
DE DAITAI I think we can show in the greenhouse that several lon-‘land selections. when
grown as upland rice. have very high degree of drought tolerance. When I say high l mean
pretty close to l5 bar soil-moisture tension. This is surprising because under field conditions
moisture tension as low" as lS-centibar would reduce grain yield by one-third. yet some of these