Breeding effects on the root-associated microbiome of

Modern crop varieties may exert reduced influence on their microbiome compared to their progenitors, as plant-microbe interactions were not targeted during breeding. Moreover, formerly beneficial microbiome functions might no longer be relevant in modern agricultural ecosystems. We hypothesised that such patterns could become particularly evident under drought, since drought-tolerance has not been a primary breeding target. To test this, we grew six maize landraces (released before 1945) and six modern varieties (released from 2010 onwards) in a field under ambient and 60% reduced precipitation. The experiment was repeated over two years, differing in amounts and temporal distributions of precipitation. We assessed the composition of root-associated prokaryotic communities during grain filling by 16S rRNA gene metabarcoding. Intra-variety dispersion in microbiome composition relative to plant biomass-based dispersion was higher in modern varieties, suggesting breeding may have affected plant control over microbiomes. Besides that, shifts in microbiome composition between landraces and modern varieties were driven mainly by the plants' impact on soil water potentials. Consequently, the taxa that increased in relative abundance during soil drying, mainly