Endophytic bacteria of wheat and the potential to improve microelement composition of grain

Abstract

In sustainable agriculture, there is a tendency for an increased use of microbiological preparations, especially plant growth promoting bacteria (PGPB), that can supplement the phenotypic plasticity and adaptability of plants, stimulate their growth and development, increase resistance to stress. The endophytic PGPB could be a promising element of technologies for the improvement of mineral nutrition and promotion of growth and yield of wheat (Triticum spp.). They are transferred to the plant by a horizontal, from the environment (rhizosphere, phyllosphere), or a vertical, from the seeds (from generation to generation), way. The growth-promoting effect of endophytes is mediated by the synthesis and secretion of phytohormones and secondary metabolites as well as their ability to absorb N₂, suppress the development of bacterial and/or fungal phytopathogens; improve mineral nutrition. The review elucidates current data on the presence of bacterial endophytes in various organs of wheat plants and their characterization as potential PGPB. Data on the most common genera of bacterial endophytes of wheat (Bacillus, Micrococcus, Staphylococcus, Pseudomonas, Pantoea, Kosakonia, etc.) are presented, and their influence on plants is described, in particular, the effect on the absorption of micronutrients important for plants and humans such as iron (Fe) and zinc (Zn), resistance to stress factors and growth. The varietal differences in the wheat endophytic microbiome are noted. An increased micronutrient absorption and assimilation assisted by the bacterial endophytes are associated with the changes in endogenous auxins and ethylene, the release of organic acids, siderophores, indirect activation of metal transporters, etc. The mechanisms underlying plant growth stimulation are complex due to interactions between a microorganism and the whole plant microbiome and their changes during the plant ontogenesis. The analysis of the published data confirms the need for further studies of the species composition and mechanisms of interaction of endophytic PGPB to develop new strategies for improving mineral nutrition of wheat and trace element biofortification of grain. It is a feasible and promising technology of the future to overcome the problems of hidden hunger and provide quality food products to the world population with available resources and a reduced negative impact on the environment. Keywords: bacterial endophytes, PGPB, wheat, biofortification, Zn, Fe