Vergara - 1976 - Physiological and morphological adaptability of ri

RESPONSE TO DEEP twxrsa STRESS 30?
During the vegetative-to-panicle initiation stage. the most susceptible stage in
terms of grain yield reduction as a result of submergcnee differed w'ith the
variety being used (Palada, 197(1). 1n one case panicle initiation was the most
sensitive. since spikelet number was greatly reduced. In another. the seedling
stage was most damaging. since most of the plants were killed.
Temperature of water
The percentage of sunrival is greater at lower than at higher temperatures
(Kondo and Okamura. 1932; Palada and Vergara. 1972). Using clear water.
Kondo and Okamtlra (1932) showed that plants die in 8 days at 30°C 6 days at
35°C, and 4 days at 40°C. 'l'he_y also reported that iftlie riee plant is kept flooded
for a long time in warm water during grain formation. the grains will germinate
in the particle.
Oxygen content is associated with temperature. The Wanner the water. the
lower its oxygen content and the more the rice plant suffers from oxygen defi—
ciency Kondo and Okamura (1934b) reported greater damage at lower oxyfgen
content s0 that aeration or water turbulence decreased the damage.
Unfortunately’. we do not know the temperature of the water under field
conditions when the plants are submerged.
Duration of submergence
The percentage of survival of seedlings decreases with the duration of submergenee
(Palada and Vergara. 1972). Percentage of survival decreased sharply
after 6 days of submergence. Some rice plants have been reported to survive
submergenee for at least 10 days (Alim et al.. 1962) and even up to 2O day's
(Dikshit and Maurya. 1971).
Turbidity of water
There is less damage and higher survival when plants are submerged in clear
“rater as compared to muddy water (Kondo and Okamura. 1934a; Palada and
Vergara. 1972). Kondo and Okamura (l934a) attributed the decrease in survival
to mud that adhered to the plants even after submergenee. On the other hand.
the decrease in light intensity available to the plants may be the main cause of
low survival in turbid water. as suggested by Palada and Vergara (1972). Yamada
(1959) reported that photosynthesis occurs even during submergence.
Light intensity and water depth
The percentage of survival of submerged plants is significantly higher at higher
light intensity (Palada and Vergara. 1972). The percentage of light received by
submerged plants would naturally depend on the turbidity of the water and
depth of submergence. There is a decrease in survival of the plants with increase
in water depth (Alim et al. 1962; Palada and Vergara. 1972).
Nitrogen status
Plants with more initial carbohydrates survive better (Palada and Vergara.
1972). Starch content is probably an important factor that affects the resistance