Abstract
Drought reduces growth and yield in rice. Three pot experiments were performed
in consecutive years, 2013 and 2014 in two aman seasons under drought (40%
field capacity, FC) and control (100% field capacity, FC) irrigations to study
drought tolerance mechanism(s) based on morphological, physiological and
biochemical traits, and yield attributes in aromatic rice. Twelve treatments (6
genotypes × 2 irrigations) were arranged in CRD and experiment was carried out
at Bangladesh Institute of Nuclear Agriculture, Bangladesh Agricultural
University, Mymensingh. In the 1st expt., drought was imposed at panicle
initiation stage where morphological and physiological data were recorded; while
in the 2nd expt. drought was imposed at grain filling stage where important
physiological and biochemical traits of flag leaf were estimated; and in the 3rd
expt. drought stress was imposed at grain filling stage and, yield and yield
attributes were recorded at maturity. Important morphological, growth,
physiological and yield attributes were significantly (P>0.05) decreased at 40% FC
in both the years. Compared to control, relative reduction at 40% FC in above
parameters, genotypes were classified into tolerant (Binadhan-13 and NERICА
mutant) and sensitive (RM-100-16, Ukunimodhu, Kalizira, and BRRI dhan34)
categories. Tolerant genotypes had smaller reduction in shoot and root DM (av.
7.73 and 5.56 %, respectively) than sensitive ones (av. 19.32 and 21.80%,
respectively). During drought stress proline and sugar accumulation (78.09 and
35.96%, respectively) increased in tolerant genotypes compared to sensitive
genotypes (14.19 and 11.29%, respectively). At 40 % FC, relative reduction of yield
attributes and yield (effective tillers hill-1, total spikelets panicle-1, filled spikelets
panicle-1, 1000-grain weight and grain yield hill-¹) was also lower in tolerant (9.48,
7.85, 10.44, 1.82 and 8.16%, respectively) than sensitive genotypes (24.23, 24.25,
14.71, 8.17 and 15.51 %, respectively). All traits and yield attributes across the
three experiments showed significant (P>0.05) decrease except proline and total
sugar which significantly increased under drought. Low reduction percentages of
the traits under drought stress to that of the control discriminated Binadhan-13
and NERICA mutant genotypes consistently as drought tolerant. Important
drought tolerance mechanisms were: (i) higher root and shoot ration, (ii)
increased osmolytes accumulation (proline and total soluble sugar) of flag leaf,
and (iii) lower yield reduction under drought in rice plant.