Abstract
AHMED, MUKHLESUR RAHMAN. Institute of Graduate Studies, Central
Luzon State University, Muñoz, Nueva Ecija, Philippines, March 1992.
INFLUENCE OF WATER DEFICIT ON WATER RELATIONS, GROWTH, AND YIELD OF
DRY SEEDED RICE.
Advisor: Dr. Josue A. Irabagon
Co-Advisor: Dr. Keith T. Ingram
Experiments were conducted at the experimental farm and in the
greenhouse of the International Rice Research Institute (IRRI) from
December 1990 to November 1991 to investigate the effects of
vegetative and reproductive water deficit on crop growth, grain yield
and water relations of rice. The field experiment was laid out in a
split-plot design with three irrigation levels (well-watered control,
vegetative, and reproductive water deficit) in the main plot and four
rice cultivars (BR20, BR21, IR64, and IR72) in the subplot, each with
six replications. The greenhouse experiment was conducted in a
factorial randomized complete block design using the same treatments
with three replications.
Both vegetative and reproductive water deficit reduced plant
height, leaf area index, light interception, root and shoot dry
matter, root length density (RLD), and decreased leaf water potential,
osmotic potential and turgor, and increased leaf rolling and drying.
After re-irrigation, vegetative stressed plants recovered completely and performed similarly to well-watered plants. Reproductive stress
plants, however did not recover except plant water relation variables
and thereby reduced shoot dry matter, yield components, and final
grain yield. Water deficit significantly delayed flowering and
maturity. The major effects of reproductive water deficit were
incomplete exsertion of panicles, spikelet desiccation, increased
fraction of unfilled spikelets, reduced 1000-grain weight, and harvest
index.
In the field experiment cultivars responded similarly to water
deficit. BR20 generally had greater RLD in the 20-40 cm soil layer
and maintained higher turgor during stress indicating its better
drought avoidance capacity.
In the greenhouse trial, cultivars responded differently to
water deficit. IR72 had the greatest total evapotranspiration (ET)
during both vegetative and reproductive water deficit, and BR20 had
the least. The least ET in BR20 was related to lesser stomatal
conductance. Thus, BR20 maintained higher plant water status which is
a drought avoidance mechanism. After rewatering, both vegetative and
reproudctive stress plants recovered except IR72 which died during
reproductive stress. The best recovery among vegetative stress plants
was observed in IR72 and was attributed to its greater root dry
matter. Water deficit significantly decreased panicle exsertion rate.
Earliness and faster panicle exsertion is important drought escape
mechanism of BR21.