Combined pre-seed treatment with microbial inoculants and Mo nanoparticles changes composition of root exudates and rhizosphere microbiome structure of chickpea (Cicer arietinum L.) plants

Chickpea (Cicer arietinum L.), a valuable legume crop, is an essential component of diet in many Asian, African, European and American countries. A major role in increasing its adaptive potential, quality and quantity of the yield is played by symbiotic and associative bacteria. The main aim of this research was to study the effect of combined pre-seed treatment with microbial inoculants and Mo nanoparticles on the composition of root exudates and the taxonomic diversity of microorganisms in the chickpea plants rhizosphere. We studied seed germination, the activity of enzymes involved in antioxidant protection system and the formation of plant-microbial system under the influence of nodule and rhizosphere bacteria and molybdenum (Mo) nanoparticles introduced into seeds before sowing. Rhizosphere microbiome was studied with the help of pyrosequencing method. Maximum numbers of introduced bacteria were observed in variants with Mo nanoparticles. The symbiotic effectiveness of Mesorhizobium ciceri strain ST282 was further improved by co-inoculation with helper bacteria Bacillus subtilis and Mo nanoparticles. Effective symbiosis was shown to be an important factor determining the formation of the rhizosphere microbiome by the representatives of the order Rhizobiales and influencing the numbers and the composition of the rhizosphere microbial community. A self-sufficient legume-rhizobium symbiosis improved the physiological status of the plant, increasing structural diversity of the microbial community of the rhizosphere through changes in the activity of root exudates, and paved the way for the development of the most effective associative bacteria.