Impact of thermal stress on the germination and early growth of soybean seedlings

Soybean is cultivated over a large area in various countries, being subject to different environmental conditions where abiotic stresses such as drought and high temperature are recurrent. Therefore, this research aimed to evaluate the physiological response of soybean seeds with contrasting vigor, subjected to high-temperature stress. The study was conducted in two experiments, both in a completely randomized design and factorial arrangement, with four replications. Initially, the response of high and low vigor seeds was assessed when subjected to thermal stress for different periods, evaluating this response with variables related to germination. Subsequently, an experiment was conducted to evaluate the physiological response of high and low vigor seeds. Seeds classified as high vigor were used, with part of the lot artificially aged in the laboratory to reduce vigor for the experiments. Thermal stress was imposed in an oven at 38 °C, applied after radicle protrusion. Analysis of variance confirmed the significant influence of vigor, both in isolation and in interaction with stress and time, on the seedling characteristics. These results demonstrated that high vigor seeds showed better performance in variables such as normal seedlings, axis dry mass, seedling length, and reserve mobilization, even under stress conditions and over time in the physiological response experiment. This fact reinforces the need for using high vigor seeds to optimize the growth and development of soybean crops, particularly in environments subject to thermal stress.