B.Sc.-M.Sc. Int.

The study entitled “Assessment of multiple abiotic stress tolerance mechanisms in rice (Oryza sativa L.)” undertaken at the Department of Plant Physiology, College of Agriculture, Vellayani during 2018-19. The objective was to study the multiple abiotic viz. drought, salinity and high temperature stress tolerance mechanisms in rice and to validate the identified QTLs for stress tolerance in rice.
The investigation comprises four experiments, In experiment I initial screening of 20 rice genotypes for single abiotic stress tolerance was studied. Stresses were induced using different concentrations of PEG6000, NaCl and temperature controlled incubator for providing drought, salinity and temperature stresses respectively. Germination study was carried out using paper towel method. In the first experiment drought stress were given at concentrations -1bar, -3bar, 5bar and -7bar water potentials of PEG6000, salinity stress was given at 100mM, 150mM, 200mM, 250mM NaCl and temperature stress were given at 350C, 400C, 450C and 500C for all 20 rice varieties with two replications. The physio-morphological and biochemical parameters were studied on 14th day of germination.
The highest level drought, salinity and temperature stresses at which germination occurred was selected as Dh (-5 bar), Sh (250mM NaCl) and temperature (Th) (350C) respectively. Among 20 rice varieties, PTB-7, PTB-60 and PTB-35 showed maximum seedling vigour at highest level of drought stress (Dh) stress condition Vyttila-9, MO-18 and Vyttila-3 recorded maximum seedling vigour index at highest tolerated level of salinity (Sh) stress condition and N-22, NL-44 and Vyttila -6 showed maximum seedling vigour index at highest tolerated level of temperature stress (Th) stress condition. These nine genotypes were selected for the evaluation of combination stress treatment
In the second experiment, The combination stress treatments given were Dh x Sh, Dh x Th, Th x Sh and Dh x Sh x Th. Rice varieties did not germinated at Dh x Sh and Dh x Th. The maximum seedling vigour index at Dh x Sh and combination stress treatment was observed in PTB-7, Vyttila-9, PTB-35 and at Th x Sh was observed in NL-44, MO-18 and N-22 respectively. These rice varieties were selected as tolerant varieties.
In experiment III six rice varieties selected from combination stress treatment were evaluated for yield parameters in pot culture experiment. The design of the experiment was CRD with two replications and one control. Drought and salt stress were imposed during reproductive stage for 5 days by applying -5bar PEG6000 and 250mM NaCl solutions respectively into the pots containing rice varieties, Temperature stress was induced using a temperature controlled polyhouse from panicle initiation to maturity stage. Physio-morphological, biochemical and yield parameters were studied under the combination stress treatments. Highest yield under the combination stress treatment of Dh x Sh was observed in PTB-7 and highest yield under the combination stress treatment Th x Sh was observed in N-22. Based on morpho-physiological and yield parameters PTB-7 was selected as the tolerant variety under drought and saline condition and N-22 was selected as the tolerant variety under temperature and salinity condition.
In experiment IV all the 20 genotypes were analyzed for the identification of reported markers linked to stress tolerance such as drought salinity and temperature. Reported microsatellite markers linked to drought, salinity and temperature were used to screen 20 rice varieties. Among the markers distinct polymorphism for temperature tolerance between temperature tolerant (N-22 and NL-44) and susceptible varieties was shown by RM 6100. RM 7076 showed distinct polymorphism in tolerant varieties PTB-7 and NL-44 . RM 1287 showed distinct polymorphism for salinity tolerance in PTB-7 and N-22. Drought tolerance between drought tolerant (PTB-7) and susceptible varieties was Shown by RM 490.