Evaluation of elite Oryza sativa L. germplasm and development of an effective hematoxylin stain-based screen for NaCl-tolerant rice at the Germination stage

One important feature distinguishing plants from other multicellular organisms is that plants are sessile and must endure diverse environmental challenges. Among the abiotic stressors, salinity stress adversely affects rice production worldwide. The present study was carried out to evaluate the degree of salt tolerance at the seed germination stage in 15 rice genotypes that are cultivated in various ecological niches. For this study, seeds were sown in petri plates at 0, 100 and 125 mmol L⁻¹ salinity stress levels in vitro. Morpho-physiological traits were measured, i.e., radicle and plumule growth, germination percentage, Na⁺/ K⁺ content and derived indices like seedling vigor index, germination index, and mean germination time. Salt tolerant index (STI) was used to identify the most tolerant genotypes at the seed germination stage. Hierarchical Clustering and Pairwise correlation analysis also resulted in a clear demarcation of genotypes based on similarities in salt tolerance. From these observations, it was concluded that genotypes CSR10, KS12, RNR 15048 and GGV-05-01 could be used in breeding experiments for salt tolerance. Furthermore, the salt-tolerant genotypes accumulated less Na⁺ in comparison to the sensitive genotypes, IR29. The K⁺/Na⁺ ratio was found to be the strongest determinant of salinity stress. A unique and rapid screening method of staining the radicle with a Hematoxylin stain showed it to be convenient and reliable. The findings of stain uptake were further validated using the established genotoxic agent, H₂O₂. A dose and time-dependent uptake of Hematoxylin stain was observed with salinity stress.