Maize landraces under water deficit favor diverse rhizosphere communities associated with improved stress response

Climate change is intensifying water scarcity, posing major challenges to global crop productivity. Improving tolerance to limited water availability is therefore a key agricultural priority. While elite genotypes are widely used in breeding, maize landraces represent an underexploited reservoir of adaptive traits. Their interaction with soil microbial communities may play an important role in stress resilience that needs further investigation to have its extent fully understood. In this study, we investigated the rhizosphere microbiota of four maize landraces from Lombardy (Northern Italy) to assess how soil origin, plant genotype, and water availability interact in shaping bacterial communities. Plants were cultivated in soils collected from four locations, first under wellwatered conditions and then exposed to water deficit. Growth and photosynthetic traits were monitored in parallel to link microbial composition with plant performance. Under well-watered conditions, rhizosphere communities were strongly shaped by the soil–genotype combination, with consistent enrichment of Bacillota taxa. Under water deficit, however, most landraces/soil combinations exhibited a reduced rhizosphere effect that brought rhizosphere bacterial communities to become indistinguishable from bulk soil. Strikingly, landraces displaying the best tolerance to water deficit showed an increase of biodiversity in the rhizosphere bacterial community, suggesting a recruitment strategy opposing that shown in well-watered conditions. These results highlight the importance of integrating landrace diversity and microbiome interactions into strategies for improving maize resilience. The study demonstrates that not only soil and genotype, but also the capacity to sustain distinctive and diverse microbial associations under stress, may contribute to plant performance in water limited environments.