Uncovering genetic linkages in the rhizosphere contributing to adaptation

Microorganisms assembled into the plant rhizosphere from the surrounding soil can benefit the fitness of their host. Variation in plant genetics is associated with variation in rhizosphere microbial community composition leading to increased fitness and crop production and reducing reliance on synthetic agricultural inputs through selection. However, what impact the abiotic environment has on connections between microbes and host genetics, and whether those connections in turn impact crop performance in realistic agricultural scenarios is still unclear. We assessed agronomic performance and 16S sequence-based rhizosphere bacterial community composition on a large diverse barley population grown in seven field trials across four locations and two years. Within adapted regions, we observed consistent rhizosphere compositions across diverse soils, whereas in unadapted environments, distinct microbial communities were recruited, indicating environmental specificity in microbial assembly. Greenhouse trials further revealed that abiotic soil properties and microbial inoculants together interact to modulate rhizosphere composition and plant growth. Genome-wide association studies identified hundreds of quantitative trait loci (QTL) for microbial traits, with thirty of those loci co-localizing with agronomic traits, suggesting interspecies pleiotropy or genetic linkage. At specific loci, candidate genes associated with root-microbe interactions, including those related to pathogen response and root exudate production, suggest mechanisms that enable adaptation to local environments. These findings support the idea that genetic manipulation of rhizosphere microbiomes via selection of crops could enhance adaptation (i.e., yield, quality) across variable environments, advancing breeding strategies for improved crop resilience and productivity.