Biozyme® e Microalga Parachlorella sp. Via sementes: estratégia para aliviar os efeitos do déficit hídrico na fisiologia do milho

Abstract

Maize (Zea mays L.) is of great agricultural and economic importance in Brazil; however, its productivity is strongly affected by water deficit, which causes changes in gas exchange and in the photochemical functioning of plants. In this context, biostimulants and bioinputs, such as Biozyme® and the microalga Parachlorella sp., have been studied as alternatives to support plant physiological balance under stress conditions. This study aimed to evaluate the potential of seed inoculation with Biozyme® and Parachlorella sp., applied alone or in combination, to reduce the stressful effects of water deficit on the photosynthetic metabolism of maize plants. The experiment was carried out in a randomized block design, in a 6 × 2 factorial scheme, consisting of six cultivation conditions and two evaluation periods, with four replicates. Seeds of the variety SEMPRE20A38 VIP3 were inoculated with Biozyme® and/or Parachlorella sp., and plants at the V4 growth stage were exposed to irrigated control or water deficit induced by irrigation suspension. Evaluations were performed at 4 and 7 days after irrigation suspension, considering gas exchange, water use efficiency, relative chlorophyll index, and chlorophyll a fluorescence variables. Data were subjected to analysis of variance, and means were compared using the Scott-Knott test for treatments and the LSD t-test for evaluation periods (p ≤ 0.05). At 4 days, there was no significant difference among treatments for net CO₂ assimilation, but the association between Biozyme® and Parachlorella sp. promoted higher water use efficiency. At 7 days, water deficit reduced gas exchange; however, plants treated only with Parachlorella sp. under water deficit showed higher net CO₂ assimilation, transpiration, and stomatal conductance than plants under water deficit alone, in addition to maintaining the electron transport rate at levels similar to those of irrigated controls. Biozyme®, applied alone or associated with the microalga, promoted punctual responses, mainly related to the relative maintenance of chlorophyll index and initial water use efficiency, but did not maintain photosynthesis or electron transport under stress. It is concluded that Parachlorella sp. showed greater potential for physiological mitigation of water deficit, whereas Biozyme® promoted initial or specific responses, without eliminating the negative effects of water restriction.