Contribution of seed-endophytic bacteria to drought tolerance in early developmental stages of native maize landraces from arid milpas

Aims Milpas are traditional agroecosystems found in rural areas of Mexico, where low input practices favor the presence of microbial associates with greater abundance and diversity than modern crops. Milpas can be found in a wide range of climates, but the beneficial functions of microbes are yet to be explored across biotic and abiotic conditions. In semi-arid regions of Hidalgo, Mexico, maize landraces have been selected to grow in milpas despite low rainfall and we hypothesized that associated bacteria contribute to the drought tolerance of these plants. Methods We collected maize seeds from arid and tropical milpas , as well as hybrid varieties from modern crops to test their responses to drought during germination and early vegetative growth; next, we studied the role of seed endophytic bacteria for this trait. Results Landraces from arid milpas displayed decreased phenotypic responses to drought (i.e. increased tolerance), and elimination of seed-endophytic bacteria from these landraces reduced germination in drought. Next, 16 S amplicon sequencing revealed that drought-tolerant landraces harbor Pseudomonas spp., Brachybacterium spp., and strains from the Bacilli class that were not found in drought-sensitive varieties; likewise, culturing methods allowed the isolation of these bacterial groups. Finally, inoculation of Pseudomonas spp. and Brachybacterium sp. strains improved the germination of a drought-sensitive variety. Conclusions Our results indicate that seed-endophytic bacteria associated to maize landraces from arid milpas contribute to drought tolerance in early developmental stages and support that ancestral practices manifest in the microbial ecology of milpas , selecting beneficial microbes to cope with local conditions.