MSc

Moisture stress during the crop ontogeny has been one of the main constraints
for sustainable rice productivity, especially in uplands. Crop losses vary depending
upon the intensity and duration of drought and growth stages. The solution to
overcome this lies in either making water available for crop growth or breeding
drought resistant cultivars. Increased irrigation inputs are not a viable option because
the water resources are unavailable or limited. Improvements in crop drought
tolerance are, therefore, sought through plant breeding. Consequently, a need to
elucidate the response of genotypes, in cultivation in the uplands of Kerala, with the
timing of drought was felt. A study was thus envisaged to characterize rice genotypes
suitable for upland cultivation and elucidate their response to moisture stress.
Twenty one rice genotypes consisting of nine high yielding varieties and
twelve traditional rice varieties were evaluated in an upland field trial (Experiment I:
Morphological characterization of rice genotypes for yield and yield attributes) as
well under controlled moisture regimes (Experiment II: Characterization of rice
genotypes for drought tolerance). Experiment II comprised of two sub experiments i)
Rapid evaluation test for drought tolerance [Experiment II (A)] and ii)
Characterisation of rice genotypes for drought tolerance under controlled moisture
regimes [Experiment II (B)]. All experiments were conducted at College of
Horticulture, Kerala Agricultural University, Vellanikkara during 2014-2015.
Results of the upland field experiment revealed existence of wide variability
among the twenty one genotypes for yield and yield attributes indicating ample scope
for improvement of the traits through selection. Early maturity, higher chlorophyll
stability index (CSI), productive tillers, spikelet fertility and plant height being
advantageous in uplands, genotype Parambankayama followed by Karanavara was
found to be the most promising. Other promising genotypes for upland cultivation
included PTB 28, Nerica, PTB 60, Karuthamodan, Kalladiaryan, Parambuvattan,
Karuthadukkan, Arimodan and Thottacheera. Most of these genotypes recorded high
chlorophyll stability index.
On rapid evaluation for drought tolerance [Experiment II (A)] conducted as
per the method advocated by Bouslama and Schapauugh (1984), moisture stress (- 6
bars) was found to affect the germination and early seedling growth parameters.
Considering that higher speed of germination, shoot and root length, seedling vigour
index and biomass under moisture stress are indicative of the capacity of genotypes to
combat moisture stress, genotype Parambuvattan followed by Arimodan was found to
be the most promising. Karuthamodan, Karanavara, Parambankayama, Kalladiaryan,
Thottacheera, PTB 60, Nerica and Karuthadukkan were the other promising
genotypes. Speed of germination and seedling vigour index were found to be high in
these genotypes
Based on the outcome of upland field experiment and the laboratory screening
study, ten promising drought tolerant genotypes were selected to delineate their
response towards moisture stress [Experiment II (B)] imposed at seedling stage (15
day after sowing), vegetative stage (35 day after sowing) and reproductive stage (50
day after sowing). In all the population subjected to moisture stress, reduction in
relative water content, chlorophyll content, number of productive tillers per plant,
panicle length and weight, spikelets and grain per panicle, flag leaf area, 1000 grain
weight, plant height, dry weight of shoot and root, root volume, grain and straw yield
per plant and harvest index, was observed. A delay in flowering was observed on
exposure to moisture stress. The magnitude of change in different traits varied with
timing of moisture stress.
PTB 60 and Karanavara recorded the highest grain yield per plant,
irrespective of growth stage at which moisture stress was imposed. These genotypes
maintained a high number of productive tillers, grains per panicle, 1000 grain weight,
dry weight of shoot and root, root length and root volume, straw yield and harvest
index under stress. Invariably, on exposure to moisture stress at different growth
stages, Parambankayama, Nerica and Karathadukkan were found next best to PTB 60
and Karanavara .