Effect of seed bacterization with plant growth-promoting bacteria on wheat productivity and phosphorus mobility in the rhizosphere

Bacterization of the seeds of spring durum wheat with the strains of gram-positive aerobic spore-forming bacteria Bacillus subtilis IB-21 and B. subtilis IB-22 and gram-negative bacteria Advenella kashmirensis IB-K1 and Pseudomonas extremaustralis IB-K13-1A was performed to study its effect on the productivity of plants, their hormonal content and rhizosphere phosphorus (P) status in the field experiments. A. kashmirensis IB-K1 and P. extremaustralis IB-K13-1A were the most capable of mobilizing hardly soluble phosphates in vitro, while P. extremaustralis IB-K13-1A produced the greatest concentration of auxins. All the studied strains successfully colonized the plant root system, the level of colonization detected during the second leaf stage being the highest in the case of A. kashmirensis IB-K1 and B. subtilis IB-22. Seed treatment with all the tested bacterial species resulted in an increase in phosphate mobility in the rhizosphere. Auxin content in wheat roots was increased by bacterization of seeds with P. extremaustralis IB-K13-1 and B. subtilis IB-22. The maximum increase in components of wheat crop yield (the mass of grains in the main and axillary spikes) was detected during 3 vegetative periods (2016, 2017 and 2018) in the case of seed treatment with the strains inducing a significant increase in auxin content in the roots of the treated plants related to either the highest bacterial capacity of producing this hormone in vitro (in the case of P. extremaustralis IB-K13-1A) or root colonization (in the case of B. subtilis IB-22).