Effect of Azospirillum brasilense inoculation on aerial root production and nitrogen fixation in landrace and improved maize varieties in a controlled environment

Abstract

The ability of leguminous crops to fix nitrogen (N) has been essential to the planting decisions of many farmers, but grass crops have generally not been considered to have the same capacity. Nevertheless, studies have revealed many species of bacterium that fix N in association with a wide variety of grass crops. In particular, a landrace of corn from Mexico has been studied that hosts an association with these bacteria in mucilage that is produced from aerial roots along the stem. This association creates a habitat for the bacteria while allowing the crop to receive the benefits from N fixed from the air. In this study we assessed the effect of inoculating two landrace varieties and a conventional variety of maize with N fixing and non-fixing strains of Azospirillum brasilense. Differences were observed for growth and aerial root traits in response to accession, but these characteristics did not respond to inoculation. Wider aerial roots correlated with higher mucilage production. Finally, we found N fixation occurring in the mucilage of those plants inoculated with the N fixing strain of A. brasilense. Mucilage samples responded to N gas analysis to imply nitrogen fixation is occurring in the mucilage. The implications of these findings could lead to research into further associations between maize cultivars and N fixing bacteria. There are cultivars other than the landrace of Sierra Mixe that can support nitrogen fixation, and mucilage is the key to this understanding.