Physiological basis of growth and yield of low land rice cultivars grown under low light environment
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Date
2021-11-15
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Department of Plant Physiology, OUAT, Bhubaneswar
Abstract
Rice is the major food crop in the world. It ensures livelihood security of millions of people
around the world especially in economically weaker section people of Asia. Abiotic stress
including salinity, drought, high and low temperature, high and low light majorly affect the yield
of rice in plants. Among the abiotic stresses affecting rice productivity, low light stress is one of
the most persistent in India, mostly in Eastern and North Eastern states, where it has a significant
impact on agricultural productivity. Low light conditions damage rice production and strongly
influences not only duration but physiological and agronomic traits of rice. Keeping in view the
increasing threat, efforts have been made to understand the mechanism (molecular, biochemical
and physiological) underlying low light stress.
Against this background, the present investigation entitled “Physiological basis of growth and
yield of low land rice cultivars grown under low light environment” was carried out with the
major objectives of screening and characterization (physiological, biochemical and molecular) of
rice genotypes under low light stress. The entire experiment was conducted at the National Rice
Research Institute, Cuttack, Odisha. The experiment was laid out in randomized block design.
Ten rice genotypes were selected out of the fifty genotypes screened in a previous experiment
(Kharif 2016 and 2017) of the same lab under NASF funded project. Selected genotypes were
grown during Kharif 2018 and 2019. Experiment was conducted with three replications during
Kharif season under Normal Light, 75% light intensity (25% light cut off) and 50% light intensity
(50% light cut off). The low light treatment was imposed by putting agro-shade net of different
light intensities mounted on a hardwood frame. The treatment was imposed at 30 DAT.
Swarnaprabha and IR-8 were used as tolerant and susceptible checks respectively.
The observations for agronomic and morphological traits i.e. tiller m-2
, panicle m-2
, specific leaf
area (SLA). Specific leaf weight (SLW), root length, root weight, plant height, shoot weight,
yield attributing parameters were recorded during flowering and harvest stages. Correspondingly,
physiological parameters (Net assimilation Rate, Stomatal Conductance, Transpiration rate,
Fv/Fm, A/Ci, WUE) and biochemical parameters (total chlorophyll content, chl a, chl b, starch
content, total Soluble Sugar content, Superoxide Dismutase, Catalase, Peroxidase) were recorded.
Among the ten rice genotypes, Panindra, PS-3 along with Swarnaprabha performed better and
were found to be tolerant than other genotypes for low light conditions. Swarnaprabha and
Panindra performed better for yield attributing traits (grain yield, thousand grain weight, Harvest
Index) among all the varieties. For studying the possible mechanism behind, we targeted and
studied the expression of genes responsible for photosynthesis and starch synthesis i.e “SourceSink concept”. The expression analysis revealed non-significant down regulation of selected
genes in Panindra and PS-3 along with Swarnaprabha whereas susceptible genotypes HKR-126
and IR-8 reported significant down regulation under low light stress. These results clearly
indicate the light modulated activity of photosynthetic and starch biosynthetic genes. Though the
exact pathway underlying is not clearly understood, the results indicate the potential of exploring
the selected tolerant genotypes (Panindra, PS-3 and Swarnaprabha) as model plant for
understanding low light stress in crop plants.