Role of Gibberellic Acid and Cytokinin in Improving Grain Zn Accumulation and Yields of Rice (Oryza sativa L.)

Purpose Low grain zinc (Zn) content in cereal crops is a major nutritional constraint which is due to Zn deficient soils and its poor translocation from the source to the sink. The study was aimed to improve the translocation and accumulation of Zn in rice grains by the application of phytohormones like gibberellic acid (GA) and cytokinin.Methods The study was carried out in three replications of seven levels of phytohormones (0, 10, 20 mg GA L-1; 10, 20 mg cytokinin L-1, 10 mg each of GA + cytokinin L-1 and 20 mg each of GA + cytokinin L-1) and three modes of Zn application, i.e., control (Zn0), soil application (ZnS), and soil + foliar application (ZnS + F). Four rice varieties (Jaya, NDR359, PD16, and Pant Sugandh 17) were tested under various treatments for superoxide dismutase (SOD), carbonic anhydrase (CA) activities, grain and straw yield, and Zn content in various plant parts in three factorial completely randomized block design.Results Activities of CA and SOD enzymes were increased by 49.5% and 53.3% in variety PD16 with 20 mg L-1 of cytokinin and 10 mg L-1 of GA respectively, under ZnS + F method. Variety PD16 produced maximum grain (61.5% greater than control) and straw yield (32.3% greater than control) by the foliar spray of 10 mg L-1 of GA and 20 mg L-1 of GA respectively, under ZnS + F mode. As regard the concentration of Zn, Pant Sugandh 17 accumulated the maximum Zn concentration in all the plant parts (leaves, pseudostem, intact, and dehusked grains). Foliar spray of 10 and 20 mg L(-1 )GA along with ZnS + F mode was noted to be the most effective strategy to increase the Zn accumulation and improved the Zn concentration in dehusked grains by 72.8% than control.Conclusion Overall, this study highlighted the soil + foliar method of Zn application along with 10 and 20 mg L-1 GA, which is a promising method to enhance the grain biofortification of rice varieties.