Influence of Plant Developmental Phase and Irrigation Level on Cultivable Microbiome of Maize Root

Plant growth-promoting bacteria can help plants survive in stressful environments. Here, we describe the isolation of root-surface and endophytic bacteria from maize roots at two different phases of the plant life cycle (vegetative and reproductive), grown under three different water regimes (100%, 50%, and 0%). Isolates were typed using BOX-PCR to identify unique genetic fingerprints, resulting in a total of 400 strains. These strains were screened for osmotic stress tolerance using 15% polyethylene glycol 6000. Isolates were also tested for bacterial plant growth-promoting traits, including the ability to produce siderophores, indole-3-acetic acid synthesis, and phosphate solubilization, both in the presence and absence of osmotic stress. The results showed that in the reproductive phase, a higher percentage of endophytic and rhizoplane bacteria were tolerant to osmotic stress. Additionally, the highest values of alginate and siderophore production by rhizoplane bacteria were also observed in the reproductive phase. These findings suggest that isolation of maize bacteria should consider the plant's developmental phase and hydric stress conditions to effectively select bacterial strains that enhance crop resilience in drought-affected areas.