Root Growth Dynamics, Dominant Rhizosphere Bacteria, and Correlation Between Dominant Bacterial Genera and Root Traits Through Brassica napus Development

Abstract

The plant root-rhizosphere microbial community interactions play important roles in crop production as those interactions can be beneficial, detrimental, or neutral for the plant. In Brassica napus, our current understanding of root growth dynamics and dominance of bacterial taxa and their dynamics across growth stages is insufficient. In addition, the association of root traits with dominant and potential growth promoting bacteria across growth stages under field conditions has not been well studied. Here, we use temporally intensive weekly sampling of B. napus over a ten-week period to characterize root growth dynamics, dominant rhizosphere bacterial taxa, and association between the two. We characterized the rhizosphere bacteria using high throughput sequencing of the 16S rRNA genes. B. napus root length showed distinct growth stage patterns with an increase in root length at early stages followed by s and/or gradual increase at flowering followed by reduction at maturity. Fine root length at the two-three leaf stage and seed yield were significantly positively correlated. The dominant microbial community composition was positively correlated with root traits and environmental variables, with the strongest correlation at the vegetative stage. Positive and significant correlations between individual bacterial genera and root traits were observed during vegetative stage, suggesting possible causal linkage between the two. The observed significant positive correlations between the bacterial genera and root traits and between root length and seed yield under field conditions suggest the potential for designing root development and beneficial microbial interaction-based canola breeding and management strategies.