Bacillus Co-inoculation Improves the Stomatal Conductance, Root Angulation, and Harvest Index of Maize Under Water Deficit in a Line-Source Irrigation System

Abstract The objective of this study was to evaluate the ecophysiological and agronomic characteristics and the root morphology of maize inoculated or co-inoculated with rhizobacteria at various irrigation depths (line-source) in the field. The depths were imposed from stage V5 and continuously until the end of the cycle. The experiment was carried out in the field with seven inoculant treatments: control (no inoculation), Azospirillum brasilense , Bacillus safensis and Bacillus pumilus (BSBP), Bacillus subtilis and Bacillus megaterium (BSBM), Azospirillum brasilense + BSBP., Azospirillum brasilense + BSBM, and BSBP + BSBM, and three irrigation management methods: full irrigation depth (566 mm), suboptimal irrigation depth (423 mm), and irrigation depth with water deficit (150 mm), with four replicates. Stomatal conductance, photosynthetic efficiency, relative chlorophyll content, leaf area, production components, chemical composition of dry biomass, and root morphology were evaluated. Most inoculations or co-inoculations positively affect plant morphophysiology with a reduction in irrigation depth, but this effect is not reflected in production gains. However, co-inoculation with Bacillus subtilis and Bacillus megaterium (BSBP) was the most efficient at mitigating severe water deficit in maize because it increased stomatal conductance, root angulation, and the harvest index. Rhizobacteria have proven to constitute an ecologically correct strategy that favors root development, with the aim of mitigating the effects of water deficit in maize plants.