Browsing by Author "Bindhya Mathew"

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    Physiological, biochemical and molecular characterization of saline tolerant genotypes of rice
    (Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2022-03-11) Bindhya Mathew; Veena Vighneswaran
    The study entitled “Physiological, biochemical and molecular characterization of saline tolerant genotypes of rice” was conducted at Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, during 2019-21 to screen saline tolerant rice genotypes of Kerala for the presence of Saltol QTL and to assess various physiological and biochemical parameters of salt tolerance under different stress levels. Twenty rice varieties, including one susceptible check were grown in nutrient media and soil whose electrical conductivity was maintained at three different levels viz, 6 dS m-1, 9 dS m-1 and 12 dS m-1. Experiment was conducted in two parts. Visual scoring and molecular screening were done on the genotypes in the first part and physiological and biochemical characterization of their saline tolerance were performed in the second part. For visual scoring, rice seedlings were grown hydroponically in seedling floats containing salinized Yoshida nutrient medium, for 21 days. Molecular screening was done using 20 SSR markers linked to the Saltol QTL of rice. For physiological and biochemical characterization, the genotypes were grown in pots, with soil maintained at EC of 6 dS m-1, 9 dS m-1 and 12 dS m-1. Various morphological, biometrical, physiological and biochemical parameters of salt tolerance were studied. Observations were taken at 5 stages- 21st day (seedling stage), 40th day (active tillering), 60th day (panicle initiation), at flowering and at harvest stage. On analysis of the binary marker data in NTSYSpc for genetic distance, it was found that the genotypes were diverse in terms of marker alleles and they clustered into 4 groups. The released varieties and the traditional saline tolerant landraces of Kerala are highly related and got clustered under one group. The CSR varieties were more related to FL 478, than the varieties from Kerala. Jyothi, was very unrelated to other varieties and formed a separate group. All tolerant varieties except CSR 10 and CSR 27 were polymorphic with FL 478 for atleast one of the three important markers linked to Saltol - RM1287, RM493 and RM10748, revealing that a salt tolerance mechanism other than that controlled by Saltol QTL might be in action within them. The morphological, physiological and biochemical parameters under study showed a significant variation among genotypes and treatments. The interaction between genotypes and salinity levels was significant for the observations on number of tillers per hill, grain yield, plant height, root length, fresh weight of shoot and root, dry weight of shoot and also for all biochemical parameters- chlorophyll content, sodium content, potassium content, Na+: K+ ratio, proline content and activities of catalase, peroxidase and superoxide dismutase. For all these parameters the susceptible variety showed significantly high/low values compared to the tolerant varieties except in plant height at 12 dS m-1, root length at 9 dS m-1 and 12 dS m-1, and chlorophyll content in all treatments on 21st day, 40th day and in 6 dS m-1at 60th day. Cluster analysis revealed that the genotypes clustered in a similar fashion based on the biochemical observations from 21st and 40th day, but a much different clustering was observed in 60th day, opening the possibility for a different kind of tolerance mechanism working at reproductive stage. As observed from the results of principal component analysis, at seedling stage and active tillering stage, Na+: K+ ratio had the greatest contribution to salt tolerance but at panicle initiation stage, it was the peroxidase activity. The percentage contribution of Na+ and K+ contents on the principal component 1 of salinity tolerance had reduced and that of peroxidase activity and superoxide dismutase activity increased, as the plants transitioned from seedling and tillering stage to the panicle initiation stage. Combining this observation with the polymorphism of genotypes for the important markers of Saltol, it was concluded that there could be an alternate mechanism and a genomic region, possibly a QTL, providing reproductive stage salinity tolerance to genotypes.