Functional Characterization of Culturable Rhizobacteria From Mexican Maize Landrace Palomero Toluqueño ( <i>Zea mays</i> var. <i>Everta</i> )

Palomero Toluqueño maize (PTM, Zea mays L. var. everta) is an ancient landrace cultivated in the highlands of central Mexico (2200-2800 masl) under traditional agroecosystems considered suboptimal by conventional agronomic standards, suggesting that its adaptation may be partially mediated by its associated microbiome. This study characterized the cultivable rhizobacteria associated with PTM, focusing on their functional traits and potential agronomic applications. Acidic soils with nitrogen and site-specific phosphorus deficiencies yielded 73 bacterial isolates from three conservation plots, spanning 35 genera across the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Functional screening of 60 strains revealed convergence across sites, with the Proteobacteria phylum being the most abundant and functionally diverse. Overall, 80% of the strains exhibited plant growth-promoting activities (PGPA), with 70% producing IAA, 32% solubilizing phosphate, and 43% producing siderophores. Phosphate solubilization ranged from 660 to 830 µg mL^-1 (e.g., Acinetobacter, Advenella, Pseudomonas); the siderophore production index ranged from 3.2 to 3.9 in 24 h (Enterobacter, Pseudomonas, Serratia); and IAA synthesis was notable in Achromobacter and Curtobacterium. Two relevant functional clusters were identified, comprising generalist and specialist strains. Greenhouse assays validated nine strains, particularly Pseudomonas alvandae RSPTM-03 20, Achromobacter deleyi RSPTM-01 34, and Enterobacter sp. RSPTM-03 05, which enhanced shoot growth. Pseudomonas emerged as a key functional genus, reinforcing the potential of PTM-associated bacteria as PGPR.