Zinc Biofortification to Enhance Soybean Seed Quality and Lower Cadmium Under Alkaline Conditions: The Role of Genotypes

Abstract

Zinc (Zn) biofortification is a promising agronomic approach for improving crop nutritional quality and reducing the accumulation of toxic elements in edible plant parts. The aim of the present study was to evaluate differences in Zn and Cd status and accumulation among Zn-biofortified soybean genotypes grown under alkaline soil conditions. This study was conducted in Eastern Croatia with six soybean genotypes (0–1 maturity group): Ika, Korana, Lucija, Sonja, Sunce, and Toma (Agricultural Institute Osijek, Osijek, Croatia). Foliar biofortification treatments were applied at the beginning of flowering at 0 (control), 3 kg/ha (Zn_1), and 6 kg/ha (Zn_2). Even though the genotype Ika had the highest Zn-bioconcentration value across all treatments and both years, the Toma genotype had the highest seed Zn concentration (64.87 mg/kg), whereas the Sonja genotype had the highest leaf Zn concentration (405 mg/kg). Biofortification treatments significantly (p < 0.001) increased soybean seed Zn content, with the highest increment under Zn_2. Averaged across both Zn biofortification treatments, Cd concentration in the soybean seed decreased by 33.4% in 2020 and by 45.8% in 2021 as compared to the control (31.53 and 51.47 µg/kg, respectively). Regarding the genotypes, under Zn treatment, Ika, Korana, Lucija, and Toma showed increased Zn concentrations but decreased Cd concentrations compared with the control, whereas the Sonja and Sunce genotypes showed a distinct response, with both Zn and Cd increasing under Zn treatments, indicating a possible synergistic interaction between Zn and Cd uptake. Generally, the findings indicate that foliar Zn biofortification on alkaline soil can improve soybean seed nutritional quality by increasing Zn concentration and further reduce the already low seed content of Cd.