Optimizing Biopolymer Seed Coatings: Impact of Sodium Alginate and Chitosan on the Viability of Trichoderma Harzianum, Bradyrhizobium Japonicum and Soybean Seed Quality

Insecticides and fungicides used for seed treatment are replaced by eco-friendly biopolymers derived from natural sources, such as sodium alginate and chitosan. Despite their promising potential, there are several knowledge gaps concerning the effects of these biopolymers on microbial viability and seed quality. This study aimed to i) evaluate the effect of different sodium alginate and chitosan coating formulations on the viability of Trichoderma harzianum and Bradyrhizobium japonicum during storage and ii) explore the impact of these biopolymers on soybean seed quality. The microorganisms and biopolymers were mixed with different formulations of sodium alginate, chitosan (in powder or acidic solution), and talc. Viability was assessed through colony-forming units per mL (CFU mL⁻¹) over time and soybean seed quality by radicle emergence, germination percentage and seedling growth. The results were analysed using ANOVA and Tukey’s test. Both microorganisms, incorporated in a sodium alginate layer followed by the solid chitosan/talc mixture, maintained high CFU mL⁻¹ even after 30 days of storage. However, solid chitosan mixed with talc negatively affected radicle emergence, extending to germination and seedling growth. Chitosan in an acidic solution exhibited differential activity on the viability of microorganisms, not affecting Bradyrhizobium japonicum but inhibiting Trichoderma harzianum. It did not alter radicle emergence and maximised germination. Coating soybean seeds with a specific formulation of sodium alginate, chitosan, Trichoderma harzianum, and Bradyrhizobium japonicum maintained viability during short-term storage. Adjusting the chitosan dose is crucial to avoid negative effects on soybean radicle emergence and germination.