The rhizosphere bacteriome is modified by wheat genotype and growth stage under increased imidazolinone herbicide residues

When imidazolinone herbicides persist longer than intended and remain active in the soil, they can have unknown impacts on soil health. This study investigated the impact of simulated soil residues of an imidazolinone herbicide on shoot dry matter and bacterial communities in the bulk and rhizosphere soil in tolerant and susceptible wheat genotypes, at two different crop growth stages. Four levels of gradient increased herbicide residues were applied, and rhizosphere bacterial diversity and community composition were analysed using 16S rRNA gene amplicon sequencing. Our results highlight that the shift in wheat rhizosphere bacteriome is driven more by the crop growth stage and wheat genotype than the presence and level of imidazolinone residues. Results showed a linear trend of increasing alpha diversity with increasing herbicide residues during the early crop growth stage, and a decrease in alpha diversity with increasing herbicide residues during the late crop growth stage, only for the tolerant genotype. The order Betaproteobacteriales in the rhizosphere was increased by herbicide residues to a greater extent than the other taxonomic groups. During the early growth stage, there were more ASV (amplicon sequence variant) enriched by imidazolinone herbicide residues in the rhizosphere of the tolerant genotype compared with the susceptible genotype. Future research work should consider studies with soils that have different physicochemical properties, and focus on other soil microbes of known significance to nutrient cycling and crop growth.