Prospecção de isolados microbianos de ambientes hipersalinos para redução do estresse hídrico em milho (Zea mays L.)

Abstract

Hypersaline environments, such as apicuns (supratidal flats) and salt flats, harbor highly specialized microbial communities adapted to growth under extreme salinity conditions. Due to the physiological similarity between high salinity and drought stress—both characterized by reduced osmotic potential—these microorganisms present biotechnological potential to enhance plant tolerance to water deficit in agricultural systems. This study aimed to isolate, identify, and evaluate the potential of microorganisms from the rhizosphere of halophytic plants inhabiting apicuns and salt flats to confer drought tolerance in maize (Zea mays L.). Bacterial and fungal isolates were obtained through culturomic approaches, using multiple culture media with varying NaCl concentrations (4 to 25%) and incubation temperatures, followed by molecular identification, characterization of their ability to promote drought tolerance in maize, and preservation. The experimental phase was conducted in a greenhouse using the maize hybrid Morgan 20A55, grown under controlled irrigation conditions in pots containing a RedYellow Argisol (Brazilian Soil Classification System). Plants were irrigated daily during the first five weeks and then subjected to a 14-day drought stress period, followed by rehydration at levels sufficient to meet the plants' full water demand. Biometric variables (plant height and shoot dry mass), physiological parameters (leaf temperature and relative chlorophyll content measured via SPAD index), and metabolic responses (leaf proline accumulation) were assessed, in addition to a visual drought index. Statistical analyses were performed using contrasts with irrigated and non-irrigated controls, along with non-metric multidimensional scaling (NMS) to evaluate treatment distribution based on the joint response of the measured variables. The results indicated that certain isolates significantly improved plant growth and physiological performance under drought stress, including higher biomass accumulation, increased chlorophyll and proline content, and reduced visual drought symptoms. Multivariate analyses confirmed these effects, revealing associations between specific treatments and axes related to thermal regulation and maintenance of leaf hydration.