Increased Drought Stress Tolerance in Maize Seeds by Bacillus paralicheniformis Halotolerant Endophytes Isolated from Avicennia germinans

<i>Avicennia germinans</i>, a representative of the marine coastal mangrove ecosystem, vital in the Colombian Caribbean, harbors a unique microbial diversity that could contain microorganisms with the potential to promote plant growth of agricultural species such as maize. The objective of this research was to evaluate <i>A</i>. <i>germinans</i> endophytes at different sampling sites and in diverse plant organs in order to identify the growth-promoting role of the most sodium chloride-tolerant endophyte found. These were then inoculated in maize seeds under drought stress conditions simulated by polyethylene glycol (PEG) in vitro. To this end, samples of adult <i>A</i>. <i>germinans</i> plants were collected from four mangrove ecosystems in the Colombian Caribbean. Several isolates were able to tolerate up to 15% NaCl (<i>w</i>/<i>v</i>), produce indole-3-acetic acid (IAA), show proteolytic activity, and inhibit phytopathogenic fungi. The best-performing strain, C1T-KM1901-B, was genomically identified as <i>Bacillus paralicheniformis</i> and evaluated as a bioinoculant in maize seeds under PEG-induced drought stress. Inoculation with <i>B</i>. <i>paralicheniformis</i> significantly increased germination potential and germination index of drought-resistant seeds compared to non-inoculated controls under severe drought stress conditions (40% PEG). In addition, inoculated seedlings exhibited significantly higher roots and shoot fresh and dry biomass at moderate to severe drought stress levels (15% and 20% PEG). These results are position <i>B. paralicheniformis</i> C1T-KM1901-B, isolated from <i>Avicennia germinans</i>, as a promising bioinoculant to enhance maize establishment under drought conditions.