AÇÃO DA APLICAÇÃO DE BIODEFENSIVOS MICROBIOLÓGICOS NOS ASPECTOS HIDRAÚLICOS, FISIOLÓGICOS, BIOQUÍMICOS E ANATÔMICOS DE SOJA EXPOSTA À SECA

Abstract

One of the most important challenges of the 21st century is to provide sufficient food for the growing global population in a scenario of climate change that restricts agricultural production, turning essential to seek alternatives that increase crop tolerance to water deficit. In this study, it was evaluated whether inoculation with different growth-promoting microorganisms has the capacity to intensify soybean responses to water deficit. In chapter 1, screening was carried out to define the combinations of microorganisms and form of application to be used. In screening, soybean plants were subjected to two different water regimes (irrigated or drought); and without treatment with microorganisms or exposed to eight combinations of microorganisms-based products Bio-Imune® (Bacillus subtilis BV02), Biobaci® (B. subtilis BV09), No-Nema® (Bacillus amyloliquefaciens BV03) e Tricho-Turbo® (Trichoderma. asperellum BV10)). After ten days of treatments, there were evaluated midday water potential (Ψmd), relative water content (RWC), gas exchange, electrolyte extravasation rate (ELR) and total chlorophyll content (Chltotal). The data were used to choose two products combinations that maintained the responses of water stressed plants like the control plants. Soybean plants were cultivated again and, upon reaching the R1 stage, they were exposed to two differential water regimes (irrigation and drought), alone or in combination with the products selected in the screening (BV02 + BV10 applied to leaves and BV03 + BV10 applied to seeds and leaves). After ten days of treatments, it was discovered that all plants in drought showed plasticity in the hydraulic system, being able to increase embolism tolerance. Furthermore, plants treated with microorganism-based products maintained the water status of their tissues like those of control plants, mainly because they were able to maintain greater hydraulic conductivity. The determining factors for maintaining water conductivity capacity were the greater venation density and the increase in root biomass. These factors, together, contributed to the plants treated with microorganisms had a quicker recovery after drought. In chapter 2, soybean plants were grown to the R1 stage and exposed to two water regimes (irrigation and drought), alone or in combination with microorganisms-based products (BV02 + BV10 and BV03 + BV10). The water potential, solute potential, hydraulic conductivity of the stem, stomatal and leaf xylem characterization, chloroplast pigment content, photosynthesis, nocturnal respiration, micromorphometric characters, cellular damage, antioxidant metabolism and productivity were evaluated. After ten days of treatments, it was observed that microorganisms increased water use efficiency, reducing transpiration and stomatal conductance while maximizing carbon acquisition. Stomatal closure, together with the greater hydraulic conductivity of the stem, contributed to maintaining tissue hydration. Tissue hydration and the combined action of antioxidant enzymes, in turn, were essential for reducing cellular damage caused by drought. All these factors impacted productivity, promoting a percentage increase in the number of grains and an increase in the drought tolerance index. The data obtained in both chapters allowed us to conclude that the combination of microorganisms was efficient in mitigating the negative effects of drought on hydraulic, physiological, anatomical, biochemical, and productive aspects, with promising results from a social and agronomic point of view.