Impact of foliar application of plant growth regulators and nutrients on high temperature stress mitigation in rice (oryza stavia L)

Abstract

The study entitled “Impact of foliar application of plant growth regulators and nutrients on high temperature stress mitigation in rice (Oryza sativa L.)” was conducted in the Department of Plant Physiology, College of Agriculture, Vellayani during August to December of 2018 with the objectives to study the effect of foliar application of plant growth regulators and nutrients on high temperature mitigation and to advance the flowering time by using methyl jasmonate (MeJA) in rice.

The investigation comprised two experiments. The extent of variation for various physiological, biochemical, morphological and yield parameters were assessed as an indicator of high temperature stress mitigation by using plant growth regulators and nutrients. The rice variety (Uma) utilized in the experiment was collected from IFSRS, Karamana. Plants were maintained under high temperature condition in a temperature controlled polyhouse from seedling to maturity stage with three replications. Maximum and minimum temperatures were measured daily using a thermo-hygrometer.

The first experiment was laid out in CRD with 10 treatments [Brassinosteroid (BR)-50 ppm, Boron (B)-100 ppm, Calcium chloride (CaCl2)-0.6 per cent, Salicylic acid (SA)-50 ppm, Glycine betaine (GB)-20 ppm, Pink- Pigmented Facultative Methylotrophs (PPFM)-1 per cent, 1-methyl cyclopropane (1-MCP)-50 ppm, Gibberllic acid (GA3)-50 ppm, water spray and control (no spray)] were sprayed at panicle initiation, heading and flowering stage. Physiological observations and yield parameters were recorded at 50 per cent flowering and harvesting stage respectively.

The study revealed that physiological and biochemical parameters such as cell membrane stability index (%), photosynthetic rate (μmol CO2 m-2 s-1), stomatal conductance (mmol H2O m-2 s-1) and Fv/Fm ratio were found to increase

significantly in most of the treatments under high temperature stress condition, whereas leaf temperature(°C) and transpiration rate (mmol H2O m-2 s-1) decreased. Among the treatments, BR spray significantly increased in the cell membrane stability index (141.57%), photosynthetic rate (17.50 μmol CO2 m-2 s-1), stomatal conductance (583.70 mmol H2O m-2 s-1), Fv/Fm ratio (0.74), chlorophyll stability index (109.32%), chlorophyll a/b ratio (1.28) and superoxide dismutase activity (0.33 activity g-1 min-1).

Treatments had significant effect on morphological and yield parameters over control plants. Among the treatments, GA3 spray resulted in significant increase in plant height (142.75 cm) and panicle length (21.33 cm). BR spray significantly increased the productive tillers per plant (10.25), pollen viability (80.23%), spikelet fertility percentage (75.4%) and grain yield per plant (15.87 g).

The second experiment was laid out in CRD with 10 treatments. Foliar spray of MeJA in varying concentrations was given on spikelet at different time [2mM L-1 MeJA at 7 am, 2mM L-1 MeJA at 8 am, 2mM L-1 MeJA at 9 am, 4mM L-1 MeJA at 7 am, 4mM L-1 MeJA at 8 am, 4mM L-1 MeJA at 9 am, water spray at 7 am, water spray at 8 am, water spray at 9 am and control (no spray)]. Physiological observations were taken at 50% flowering stage and yield parameters were taken at harvesting stage.

The study revealed that among the treatments, 4mM L-1 MeJA at 7 am treatment showed early anthesis (08:11 am) and also significant increase in pollen viability (61.93%), spikelet fertility (56.07%), yield per plant (8.55 g) and 1000 grain weight (21.33 g).

In the first experiment there was significant variation for physiological, biochemical, morphological and yield components among treatments. BR treatment recorded high pollen viability, spikelet fertility and grain yield per plant by improving the physiological and biochemical traits such as cell membrane

stability index, photosynthetic rate, stomatal conductance, Fv/Fm ratio, chlorophyll stability index, chlorophyll a/b ratio and superoxide dismutase activity. Hence, BR treatment can mitigate the ill effects of high temperature stress in rice. In the second experiment there was significant variation for physiological and yield components among treatments. 4mM L-1 MeJA at 7 am showed better performance for all the parameters such as anthesis time, pollen viability, spikelet fertility, yield per plant and 1000 grain weight. Hence, MeJA can advance anthesis time thereby enabling plants to escape from the severe temperature experienced at normal flowering time.