Agoussar, A. | Search bioRxiv

bioRxiv2026

Seed microbiota legacy mitigates the effect of drought in wheat

Seeds carry epiphytes and endophytes microbial partners that can shape plant fitness. However, whether these microbial communities serve as transgenerational memory systems of parental stress remains largely unstudied. Here, we combined multi-year field rainfall manipulation experiments in eastern Canada with a greenhouse experiment in western Canada to test whether seed-associated microbiota transmit drought legacies across plant generations. In the field experiment, reduced rainfall initially decreased yield in the drought-sensitive wheat cultivar (AC Nass), but selected for distinct seed bacterial endophyte communities. In subsequent generations, plants whose seed microbiota retained compositional similarity to these drought-adapted communities showed enhanced yield stability under upcoming water stress. A transgenerational field test confirmed that daughter plants derived from drought-exposed parent plants maintained performance under water limitation, whereas those from wetter origins did not. In an independent greenhouse assay using seeds from Saskatchewan fields differing in long- and short-term irrigation history, AC Nass plants from water-stress legacy sites exhibited higher photosynthetic efficiency, water-use efficiency, and root bacterial diversity under drought. Together, these findings demonstrate that seed-associated microbiota act as ecological archives of stress history, transmitting drought legacies across generations in a cultivar and year-dependent manner.

microbiology↗

bioRxiv2025

Potential mode of action of multispecies inoculums on wheat growth under water stress

Manipulating microbial communities could increase crop resistance to environmental stressors such as drought. It is, however, not clear what would be the best approach to do so and what microbial traits are important. Here, we first compare multispecies inoculums created using different approaches. The only inoculum that increased wheat fresh biomass under drought was the one created from 25 isolates that had showed a capacity to grow under high osmolarity. We then looked at two potential mechanisms of action of this inoculum: 1) direct action, by sequencing and screening the genomes of the inoculated bacteria, 2) indirect action, by sequencing the 16S rRNA gene and ITS region of rhizosphere, root and leaves microbial communities. The microbes in the inoculum harbored many traits related to plant growth promoting, competition and water stress resistance. The inoculation also resulted in significant shifts in the microbial communities associated with wheat, including some microorganisms previously reported to improve plant drought resistance. We conclude that the inoculum studied here increased wheat growth because it potentially acted on two fronts: directly, through the traits it was selected for, and indirectly, through inducing shifts in the resident plant microbial communities.

microbiology↗