Vergara - 1976 - Physiological and morphological adaptability of ri

68 CLIIMIATE AND RICE
perature. day length. solar radiation, and rainfall on rice growth and yield. I
would like to discuss what is known about the adaptability of the rice plant to
these climatic factors and the physio-morphological characters that enable the
plant to become adapted to diverse climatic conditions.
Agronomically. the wide adaptability of a rice variety refers to its high grain
yield performance over diverse climatic conditions (Finlay and Wilkinson, 1963;
Chang and Vergara. 1972). Specific adaptability of rice is the ability of the plant
to adjust to a specific adverse environmental condition in such a way’ that its
growth and performance is least affected when compared to those grown under
optimum conditions. Specific adaptability involves environmental conditions
such as deep water. salinity’. low or high temperature, etc. For example. a
variety with specific adaptability‘ to low temperature at the seedling stage may
not necessarily have high grain yields. However. this character is a requisite for
high grain yields in varieties planted in the temperate regions.
Adaptability of the rice plant to the environment is determined by its morphology
and metabolic activity’. which may vary’ according to the variety’ being
used and the stage of plant development. Differences in the metabolic pattern
insure the pliability of adaptation and are reflected ultimately in the differences
in morphological appearance of the plant as a whole (Chu and Tang, 1959). An
example of physiological as well as morphological adaptability of rice to the
environment is the greater development of air spaces and channels from leaves
to roots as a result of anaerobic conditions. Such adaptation makes possible the
planting of rice under xeric or hygric soil conditions.
Plant characters
In rice. the plant characters necessary for WlClC adaptability" to climatic
factors are:
Insensitivity to day length
This foremost requirement enables the famier to plant rice at any time of the year
in the tropics and the subtropics without great changes in growth duration. and
makes possible the introduction of ‘varieties from one latitude into another
(Chang and Vergara. 1972).
Tolerance to temperature changes
The rice variety must have low sensitivity to temperature so that it can be
planted in regions where low temperatures occur either at seedling. tillering.
reproductive stage. or in several stages of growth (Chang and Vergara. 1972).
Tolerance to high temperature is also needed in certain rice-growing areas.
Short stature
The rice plant must be short statured. stiff straw/ed. with short. erect leaves. the
better to withstand lodging forces; and have an effective plant type to utilize the
available solar radiation fully (Chandler, 1969).