MSc

ABSTRACT
Kandanulu Pravallika Date: 26-06-2020
2018-11-162 Time: 2.00- 2.30 pm
EFFECT OF HIGH TEMPERATURE STRESS ON SEED FILLING AND NUTRITIONAL QUALITY OF RICE (Oryza sativa L.)
The present study entitled “Effect of high temperature stress on seed filling and nutritional quality of rice (Oryza sativa L.)” was conducted in the Department of Seed Science and Technology, College of Agriculture, Vellayani during the period from 2018-2020 with the objective to study the effect of high temperature stress on seed filling and nutritional quality of rice.
The extent of variation for various seed quality parameters, enzymes and yield parameters were assessed as an indicator of high temperature stress from three rice varieties namely Prathyasa, Hraswa and Manuratna. These varieties were collected from Regional Research Station (RRS), Moncombu and from Agricultural Research Station (ARS), Mannuthy respectively. The experiment was laid out in CRD with two treatments such as control and high temperature conditions and replicated thrice. The plants were kept in a temperature controlled polyhouse from seedling to maturity stage. Seed quality and enzyme parameters were analyzed at 30 and 50 days after 50 percent flowering and yield parameters were taken at harvest stage.
Seed filling parameters recorded at milky and dough stage had revealed that high temperature stress condition resulted an increase of reducing sugar (14.810 mg g-1), carbohydrates (898.310 mg g-1), starch (14.961 mg g-1), and flavonoids (14.385 mg 100g-1) compared to control. However, amylose (17.692 %), seed protein (4.081 %), and anthocyanin (15.490 mg 100g-1) showed reduction under high temperature stress condition.
Activity of invertase was reduced under high temperature condition compared to control in all varieties from 15 to 30 days after 50 % flowering.
Under high temperature condition, spikelet fertility percentage and grain yield/plant were reduced compared to control condition. Among three varieties, highest grain yield/plant (22.790 g/plant) and spikelet fertility percentage (80.598 %) under high temperature was recorded by Prathyasa. Average reduction of grain yield/ plant and spikelet fertility percentage under high temperature was 18.733 g/plant and 74.245 % respectively. Percentage of yield reduction was maximum for Hraswa variety (27.57 %) when compared to varieties Prathyasa (21.1 %) and Manuratna (21.18%).
Pollen viability percentage was reduced under high temperature condition compared to control. Prathyasa recorded the highest pollen viability (86.358 %) and Hraswa recorded the lowest pollen viability (77.948 %). Average reduction in pollen viability under high temperature condition was 82.653 %.
There is significant difference for seed protein content among varieties. Highest seed protein content was recorded by Hraswa. There is no significant difference between Prathyasa and Manuratna for reducing sugar content, amylose, starch, invertase and yield.
High temperature stress in rice recorded an increase of reducing sugar, carbohydrates, starch and flavonoids. Grain yield/ plant, spikelet fertility percentage, amylose, anthocyanin, seed protein and invertase activity were reduced under high temperature condition in all the varieties. Flavonoids are the secondary metabolites that are increased in high temperature condition and it helped in defense. High temperature had adverse impact on yield, spikelet fertility and pollen viability and the impact were greater in Hraswa variety.
The correlation analysis revealed that under high temperature condition yield showed positive and significant correlation with total carbohydrate, starch, anthocyanin, spikelet fertility and pollen viability. Hence it is important to identify the rice varieties
which possess the major seed filling parameters which play a vital role in increasing thermotolerance that result in giving a satisfactory grain yield even under conditions of heat stress.