Sunflower Seed Coating with Biopolymers and Trichoderma harzianum: In Vitro Evaluation Against Fungal Pathogens

Abstract

Sunflower cultivation faces the constant challenge of fungal pathogens that affect seed germination and crop establishment. A sustainable alternative to chemical fungicides is the use of biological control agents such as Trichoderma harzianum combined with natural biopolymers. Chitosan is a natural polymer with antifungal activity and is capable of inducing plant defence responses. Sodium alginate, in turn, acts as a protective agent for microorganisms under adverse environmental conditions. To optimise their application, it is essential to assess the compatibility of these substances in different formulations, particularly for seed coating. The aim of this study was to evaluate the in vitro antifungal effect of chitosan and sodium alginate formulations combined with T. harzianum and applied as sunflower seed coatings against the pathogens Alternaria helianthi; Agroathelia rolfsii, and Colletotrichum spp., previously isolated and characterised. Four treatments were evaluated: a control, 1.5% sodium alginate + Trichoderma harzianum (3.15 x 10⁶ UFC g^-1), 5% chitosan and the combination of both biopolymers with the biological agent. Radial growth was measured, and the micelial rate was calculated over 11 days. The results indicated that antifungal efficacy depended on the pathogen evaluated; formulations combining sodium alginate with Trichoderma harzianum significantly reduced the growth of the three fungi studied, whereas chitosan applied alone showed limited or no inhibitory effect, depending on the species. In conclusion, the combination of sodium alginate and Trichoderma harzianum effectively inhibited the growth of these pathogens in vitro. The efficacy of the evaluated biopolymers was pathogen-dependent, highlighting fungal specificity as a key factor.