Azospirillum brasilense and cytidine enhance lateral roots of peas

Azospirillum brasilense is a plant growth beneficial rhizobacterium (PGBR) that is used as an inoculant to enhance root architecture in grassland and crop plants. The intent of our study was to develop A. brasilense into a probiotic inoculant for peas and supplement with a seedling exudate compound, to be used together or separately. As an initial characterization of the association of A. brasilense with pea roots, we performed several pea growth experiments. Azospirillum brasilense Sp7T increased the lengths of the five longest lateral roots from each plant by 63.6% and the top 10 lateral roots across 14 plants by 30%, an effect that was abolished in an rpoN mutant and a ΔcheA1/cheA4 mutant. Azospirillum brasilense Cd increased the number of lateral roots by 76%. We detected colonization by this PGBR within the epiphytic root microbiome. To identify a pea seedling exudate compound capable of enhancing lateral pea roots, we tested 15 such compounds. Cytidine was the only one that increased the number of lateral roots, by approximately two-fold, an effect that did not require A. brasilense. We conclude that both A. brasilense and cytidine might be suitable as supplements to enhance lateral roots of pea plants.