Bacterial communities in the embryo of maize landraces: relation with susceptibility to fusarium ear rot

Maize is a staple crop, fundamental for global food security. Sustainable increases in its production are deemed necessary to meet the projected demands for food and feed in the near future. Locally adapted maize accessions (landraces) represent an untapped resource of nutritional and resistance traits for maize breeding. Among them is the capacity of establishing symbiotic relationships with distinct microbial communities, collectively referred to as the maize microbiota. Our study focused on how five different maize landraces and a reference commercial hybrid showed different susceptibility to fusarium ear rot and whether this trait could be related to a particular composition of the bacterial microbiota in the embryo, using both cultivation-independent and -dependent approaches.The cultivation-independent approach was based on metabarcoding of a portion of the 16S rRNA gene. Ecological indices and multivariate statistical analyses indicated that, the microbiota of the embryos of these maize accessions grouped in two different clusters: one made by three landraces and the commercial hybrid, and one including the remaining two landraces. The main discriminant between these clusters was the relative abundance of members of the phylum Firmicutes, which was higher in the second cluster, and data on this abundance were confirmed by absolute quantification through digital PCR assays.The cultivation-dependent approach allowed the isolation of 70 bacterial strains, mostly gram-positive and including several Firmicutes. In vitro and in vivo assays allowed the identification of 25 and 5, respectively, candidate biocontrol strains against fusarium ear rot. Strikingly, the two maize landraces that showed a different embryo microbiota composition were also those characterized by a lower susceptibility to fusarium ear rot in field.