Benzoxazinoids selectively affect maize root-associated nematode taxa.

Although the effects of plant secondary metabolites on plant defense have been studied for decades, the exact roles of secondary metabolites in shaping plant-associated microbial and nematode communities remain elusive. We evaluated the effects of benzoxazinoids (BXs), a group of secondary metabolites present in several cereals, on root-associated nematodes. We employed 18S rRNA metabarcoding to compare maize root-associated nematode communities in a bx1 knock-out maize line impaired in BX synthesis and in its parental wild type (WT). Both genotype and plant age affected nematode community composition in the roots, and the effects of BXs on nematode communities were higher in the roots compared to the rhizosphere. Differential abundance analysis and quantitative PCR showed that the root lesion nematode Pratylenchus neglectus was enriched in the bx1 mutant line, while another root lesion nematode Pratylenchus crenatus was reduced. Correlation analysis showed that BX contents in maize roots mostly correlated negatively with the relative abundance of nematode reads. However, positive correlations between BXs and nematode taxa, including several plant parasitic nematodes, were also identified. Our detailed nematode community analysis suggested differential and selective effects of BXs on soil nematodes depending on both the nematode species and BX compound.