Fluroxypyr Inhibits Maize Growth by Disturbing the Diversity of the Endophytic Bacterial Communities in Maize Roots

Fluroxypyr (4-amino-3,5-dichloro-6-fluoro-2-pyridyloxyacetic acid) is a widely used herbicide sprayed on crops worldwide. The effects of fluroxypyr on maize growth and the soil microbial community structure have not been reported. In this study, the impacts of fluroxypyr on maize growth and the bacterial community structure in endophytes and rhizospheric/non-rhizospheric soils were evaluated. We found that the community structures of the non-rhizospheric and rhizospheric soils were similar. The alpha diversity showed that the richness of the endophytic communities in the mature maize roots was reduced after herbicide application. No statistically significant differences were observed between the fluroxypyr-treated and control soils in either the non-rhizospheric or rhizospheric soils. However, the composition of the endophytic bacterial community structure suggested that fluroxypyr led to a 59.1% reduction in the abundance of Acinetobacter and a 75.6% reduction in Agrobacterium, both of which are considered growth-promoting bacteria. In addition, we observed a negative effect of fluroxypyr on maize growth, including a decreased ear length and root size and a reduction in the 100-grain weight. In summary, our study suggests that fluroxypyr may negatively impact the mature growth of maize by reducing the abundance of Bacillus kineticus and Agrobacterium tumefaciens in the endophytic community of the mature root system.