Phytotoxic responses of soybean seeds to chemical seed-treatment products after storage and under contrasting water availability

Seed treatment (ST) with phytosanitary products is essential for crop protection, yet products may cause phytotoxic responses, particularly after storage. How these responses vary among products, after different storage periods and depending on water availability during germination remains poorly characterised. Phytotoxicity was evaluated in soybean (cv. Olimpo) seeds treated with 12 seed treatment products (five fungicides, five insecticides and two nematicides). Seeds were evaluated at 0 and 3 months of storage using germination tests, seedling emergence tests under controlled and uncontrolled conditions with and without water deficit, and measurements of root and total seedling length. A phytotoxicity index was calculated against the untreated control and an exploratory multivariate approach was used to compare response profiles among products within each test condition. The imidacloprid + thiodicarb product showed the greatest phytotoxic response, reducing normal seedlings by up to 22 percentage points after three months. Storage for three months was associated with lower physiological performance for several products, although responses varied according to the assay and water regime. Fungicide products were associated with greater reductions in emergence and root development under water deficit. The fluopyram product produced a halo-effect symptom on the cotyledons without a consistent reduction in physiological performance. The multivariate approach separated products into response groups that differed among test conditions.