Screening of Salt-Tolerant Rice Landraces by Seedling Stage Phenotyping and Dissecting Biochemical Determinants of Tolerance Mechanism

Abstract

Genetic diversity is a useful resource for crop improvement. In this study, a total of 28 rice genotypes were screened to isolate potential salt-tolerant genotypes at the seedling stage using hydroponic system. Different morpho-physiological indicators were used to classify tolerant and susceptible genotypes and biochemical determinants were dissected to clarify the underlying tolerance mechanism. Rice seedling were treated with two salinity levels (EC-1.1 dSm‒1 (control) and EC-7 dSm‒1) for 18 days. Salt stress resulted in significant decrease of growth and physiological traits in all genotypes; however, the lowest reduction was observed in some salt-tolerant genotypes namely Ghunsi, Nonabokra, Hogla, Holdegotal, Vusieri, and Kanchon. Cluster analysis considering percent reduction of growth parameters categorized the genotypes into four main sub-clusters and importantly, the salt-tolerant landraces were placed in the same cluster (cluster-II) with salt-tolerant check genotypes. The results of principle component analyses also demonstrated highly salt-tolerant genotypes were Vusieri > Nonabokra > Ghunsi > Hogla > Holdegotal > Kanchon. To explore the potential biochemical basis of salt stress tolerance, three tolerant genotypes were further characterized along with a salt-sensitive genotype. The higher K+/Na+ ratios noted for all salt-tolerant landraces thus indicating that the K+/Na+ ratio serves as a reliable indicator of salt tolerance in rice. The higher increment of proline content, catalase, ascorbate peroxidase activities, and comparatively lower accumulation of H2O2 and MDA were reported in salt-tolerant landraces as compared with salt-sensitive genotype. Therefore, these landraces could be utilized as promising genotypes as a source of salt-tolerant parents in the hybridization program for the development of high-yielding salt-tolerant rice variety as well as in isolating salt-tolerant genes.