Mitigation effects of selenium on accumulation of cadmium and morpho-physiological properties in rice varieties

Selenium (Se) is a beneficial element, but only when present within its permissible range. Its hyper-accumulation in edible plant parts can cause Se toxicity. This study aimed to develop an agronomic plan for biofortification of rice with Se and reclamation of cadmium (Cd)-contaminated soil, utilizing sodium selenite (Na₂SeO₃) and cadmium chloride (CdCl₂) as soil treatments. Biofortification was performed on two target rice varieties: genotypes 5097A/R2035 and GangYou725, in field trials by applying Cd at a concentration of 0-8 mg kg soil^-1 and Se at 0-1 mg kg soil^-1. Since these rice varieties have different metabolic specificity, the degree of elemental accumulation, deviations in chlorophyll concentration, activity of photosynthetic apparatus and grain yield were assessed. It was found that application of 1 mg kg^-1 Se₂O₃ decrease Cd content and increased chlorophyll content and photosynthetic activity while grain yield was unaffected by application of the metallic trace-elements. Comparing effects at different stages, we found that the 50% heading stage was most sensitive to metal application. In sum, Se mitigates Cd toxicity, but hyperaccumulation of Se (4 mg kg^-1) in polished rice was observed with Cd at 4 and 8 mg kg^-1. The elevated level of Cd stress in pot experiments resulted in over-accumulation of Se in the germ and endosperm that poses serious health concerns.