Genotype-dependent stability and specialization of arbuscular mycorrhizal fungal communities under drought in common bean.

Arbuscular mycorrhizal fungi (AMF) represent a key biological strategy for enhancing agricultural resilience under extreme climatic events such as drought. However, how AMF interact with drought-tolerant plant genotypes to sustain performance under water limitation remains poorly understood. Here, we used high-throughput DNA sequencing to investigate AMF communities associated with drought-tolerant (BAT477 and SEA5) and drought-susceptible (IAC-Milênio and IAC-80SH) common bean genotypes, integrating taxonomic, structural, and functional perspectives under contrasting water regimes. We hypothesized that drought tolerance is not simply linked to AMF presence, but rather to the ability of host genotypes to structure and stabilize their mycorrhizal communities under stress. Our results reveal genotype-specific responses to drought, with distinct community restructuring dynamics observed across individual genotypes. Drought-tolerant genotypes maintained or increased AMF relative abundance, diversity, and functional integrity under drought, whereas susceptible genotypes displayed opposing changes in the community's structure. Although most genotypes displayed high dissimilarity in AMF community structure between control and drought conditions, tolerant genotypes reorganized their communities through increase in the relative abundance of key ASVs, whereas susceptible genotypes experienced substantial reductions in abundance, diversity, and specialist ASVs. Niche occupancy and functional guild analyses further showed that AMF communities in tolerant genotypes were dominated by specialist and symbiotrophic ASVs, whereas susceptible genotypes shifted toward rare and functionally reduced assemblages. At the plant level, AMF community stability was positively associated with root biomass and negatively associated with foliar nutrient, indicating a tight coupling between mycorrhizal community structure, host nutritional status, and growth. Collectively, our findings indicate that drought tolerance in common bean emerges, at least in part, from a cooperative host-microbiome strategy in which the host actively regulates the structure and functional stability of AMF communities under water stress. These results advance our understanding of plant-mycorrhizal interactions in drought adaptation and highlight the potential of integrating mycorrhizal functionality into plant breeding strategies aimed at developing climate-resilient crops.