MSc

The experiment entitled “Validation of Temperature Induction Response (TIR) technique for inducing drought and heat stress tolerance in rice (Oryza sativa L.)” was undertaken at the Department of Plant Physiology, College of Agriculture, Vellayani during 2016-18. The objective of the study was to standardize TIR protocol for rice and to study the effect of TIR technique for combined drought and heat stress tolerance in rice.
The investigation comprised of two experiments. In the first experiment, two rice varieties namely Jyothi (Ptb-39) and Vaishak (Ptb-60) were used for the standardization of lethal and induction temperature and in the second experiment ten rice genotypes (N22, Apo, CR Dhan 305, CR Dhan 307, Ptb-7, Ptb-15, Ptb-30, Ptb-39, Ptb-43 and Ptb-60) were used to study the effect of TIR technique on combined drought and heat stress tolerance. In the first experiment 13 different treatments (T1-3: 49°C for 2, 2½ and 3 h, T4-6: 50°C for 2, 2½ and 3 h, T7-9: 51°C for 2, 2½ and 3 h, T10-12: 52°C for 2, 2½ and 3 h, T13: control) were used to identify lethal temperature and induction temperature was standardized from four treatments (T1- 28-40 ºC for 5 h & 40-52 ºC for 30 min, T2- 32-40 ºC for 5 hr & 40-52 ºC for 30 min, T3- 32-42 ºC for 5 h & 42-52 ºC for 30 min, T4- Control) with three replications.
In the first experiment 100% mortality was observed for the treatment 52°C for 3 h and was selected as lethal temperature. Maximum recovery growth and least percent reduction in recovery growth were observed under T3 (32-42 ºC for 5 h & 42-52 ºC for 30 min) and this treatment was selected as induction temperature.
The second experiment was laid out with 8 treatments [T1- TIR treated seeds + Drought + Heat, T2- TIR treated seeds + Drought, T3- TIR treated seeds + Heat, T4- TIR control,T5-Germinated seeds under ambient temperature + Drought + Heat, T6-Germinated seeds under ambient temperature + Drought, T7-Germinated seeds
under ambient temperature + Heat, T8- Control (Ambient temperature + Normal irrigation)] and three replications.
Among the genotypes, Ptb-15 recorded the highest plant height, shoot dry weight, root length and root volume. Leaf area was maximum for Ptb-43 and Apo recorded maximum root dry weight. Minimum canopy temperature was shown by N22 and Ptb-7. The genotype N22 showed the highest mean values for cell membrane stability index, chlorophyll stability index, stomatal conductance, photosynthetic rate, proline content, peroxidase activity, spikelet fertility and pollen viability. Early flowering and minimum days to 50% flowering also were recorded in N22. Productive tiller number was highest in Ptb-7 and 1000 grain weight was maximum for Ptb-43. The highest SOD activity was observed in Ptb-15. Ptb-39 (Jyothi) showed the minimum values for most of the stress related traits and yield components under various stress conditions and hence this genotype is selected as the most susceptible genotype towards both drought and heat stress conditions.
Among the treatments, T4 (TIR Induced plants without stress) recorded maximum value and T5 (non-induced plants under combined drought and heat stress) recorded minimum value for all the above mentioned morphological characters except root length. Maximum root length was recorded in T2 (induced plants under drought) and minimum in T8 (control). Peroxidase and SOD activity were highest in T2 and minimum for T5. Maximum value for yield related traits were observed for T4. Plants under combined drought and heat stress without induction showed minimum value for all the physiological and yield parameters.
The results of the present study showed that TIR technique influenced all the genotypes at various stress levels. TIR induced plants exhibited better performance on biochemical and physiological traits than non-induced plants in all the genotypes that give rise to better stress tolerance. N22 and Apo were selected as the best genotypes for stress related traits. Apart from these two, Ptb-15, Ptb-7 performed better under heat stress and drought respectively. For combined stress, Ptb-30 and
Ptb-15 were showed better performance compared to other genotypes. Ptb39 was identified as the most susceptible genotype for both drought and heat stress.
TIR induced and non-induced plants of Ptb-39 (most susceptible) and N22 (tolerant) were selected to study the changes in protein profiling and gene expression level using SDS PAGE and RT PCR. The results revealed that protein profiling showed variation between tolerant and susceptible genotypes under induced and non-induced condition for the expression of 20 kDa and 75 kDa protein. Expression level of PSTOL1 and DRO1 also showed variation between induced and non-induced plants of tolerant and susceptible genotypes. Protein synthesis was maintained significantly higher in the induced plants compared to non-induced plants on being exposed to severe stress. Tolerance of genotypes towards stress has been attributed to changing transcript levels of stress induced genes.
In the present study, T3 (32-42°C for 5 hrs & 42-52°C for 30 minutes) and T12 (52°C for 3 hrs) were selected as the induction and lethal temperatures respectively. The study also revealed that TIR technique can be used as a potential tool for improving the performance of high yielding susceptible genotypes under stress conditions.