Selênio e Iodo na Tolerância ao Estresse Térmico e na Qualidade de Frutas de Amoreiras-Preta e Framboeseiras em Regiões Subtropicais

Abstract

The Blackberry (Rubus spp.) and raspberry (Rubus idaeus) are temperate-climate fruit species expanding in Brazil, standing out for their high levels of bioactive compounds such as anthocyanins, flavonoids, and vitamin C. However, in subtropical regions they face limitations related to climatic adaptation and low soil fertility, particularly regarding the availability of micronutrients such as selenium (Se) and iodine (I). The deficiency of these elements is a global issue affecting both agricultural productivity and human health, being associated with chronic diseases, endocrine dysfunctions, and impaired physical and cognitive development. Agronomic biofortification is an efficient strategy for enhancing the nutritional value of crops, especially through foliar application of fertilizers containing essential minerals. In addition to improving the nutritional quality of food, this technique can increase plant tolerance to abiotic stresses, contributing to sustainable production. The studies carried out aimed to evaluate the effects of foliar Se and I application in blackberry and raspberry, focusing on the nutritional and functional quality of the fruits and the mitigation of thermal (abiotic) stresses. Four experiments were conducted using different combinations and doses of these micronutrients, applied at distinct developmental stages under both field and controlled conditions. In the first study, conducted with raspberry ‘Heritage’, the combined application of Se and I, particularly inorganic multi-nutrient Se with potassium iodate (KIO3), increased anthocyanins, ascorbic acid, carotenoids, total phenolics, and antioxidant activity in the fruits, demonstrating the effectiveness of the treatment in enhancing the functional profile. In the second experiment, carried out with blackberry ‘BRS Tupy’, foliar application of Se and I improved physicochemical attributes, bioactive compounds, and mineral composition of the fruits. Combinations including organic Se and KIO3 promoted higher increases in ascorbic acid, total phenolics, anthocyanins, carotenoids, and antioxidant activity, in addition to improving commercial traits such as soluble solids, SS/TA ratio, and fruit color. The third study, focused on cold tolerance in blackberry ‘BRS Tupy’, showed that the joint application of organic Se and I alleviated the negative effects of thermal stress by stimulating antioxidant enzymes (SOD, CAT, APX), increasing the accumulation of osmoprotectants (proline and soluble sugars), and preserving photosynthetic activity after exposure to -2 °C. The fourth experiment, performed with raspberry ‘Heritage’ under high temperatures, revealed that moderate Se and I combinations improved relative water content, reduced lipid peroxidation, activated the antioxidant system, and enhanced the accumulation of osmoprotectants. These treatments also preserved photosynthetic parameters such as Fv/Fm, effective quantum yield, and photochemical quenching, as evidenced by principal component analysis. Overall, the results indicate that foliar application of Se and I is a promising agronomic practice for blackberry and raspberry grown in subtropical regions, capable of simultaneously improving fruit nutritional and functional quality and enhancing plant resilience to abiotic stresses. Adoption of this strategy may contribute to sustainable management, food security, and the adaptation of temperate-climate fruit crops to climate change.