Bacterial endophytes are a class of endosymbiotic microorganisms widespread among plants that colonize intercellular and intracellular spaces of all plant compartments and do not cause plant disease or significant morphological changes. Plant and endophytic bacteria association includes vast diversity of bacterial taxa and plant hosts and in this review we present an overview of taxonomic composition of endophytes identified in common agricultural crops. Further, during the last decade, new aspects of the microbial diversity have emerged with application of new metagenomic analysis methods in studies of bacterial endophytes. Endophytic bacteria community structure is influenced by plant genotype, abiotic and biotic factors such as environment conditions, microbe -microbe interactions and plant -microbe interactions. Agricultural practices, such as soil tillage, irrigation, use of pesticides and fertilizers have a major effect on function and structure of soil and endophytic microbial populations. Therefore, the use of agricultural practices that maintain natural diversity of plant endophytic bacteria is becoming an important element of sustainable agriculture that could ensure plant productivity and quality of agricultural production. The diverse endophytic microbial communities play integral and unique role in the functioning of agroecosystems. Endophytic bacteria have been shown to have several beneficial effects on their host plant, including growth promoting activity, modulation of plant metabolism and phytohormone signalling that leads to adaptation to environmental abiotic or biotic stress. Use of endophytic bacteria presents a special interest for development of agricultural applications that ensure improved crop performance under cold, draught or contaminated soil stress conditions or enhanced disease resistance.

Bacterial endophytes are common inhabitants of plant tissues that have been shown to play an important role in regulation of plant growth and to have the potential as biological agent for plant disease protection. Only fragmented knowledge is present about endophytes that reside in the phyllosphere of cultivated tree plants such as domestic apple (Malus × domestica Borkh.). Therefore the goal of this study was to identify culturable endophytic bacteria characteristic of an apple phyllosphere and to establish biochemical traits involved in plant growth promoting activity as well as to study microbial growth suppressing activity of the endophytes. Thirty-eight putative endophytic bacteria were isolated from apple buds of cultivars 'Gala', 'Golden Delicious' and 'Orlovim' grown under field conditions and 13 of the isolates were assigned to Curtobacterium, Pantoea and Pseudomonas species. Biochemical tests revealed traits important for plant growth stimulation and microbial growth suppression characteristics of the isolates, including nitrogen fixation, production of indole-3-acetic acid (IAA), phosphate solubilization, production of siderophores and hydrogen cyanide. Several isolates displayed antagonistic activity against selected non-pathogenic and pathogenic bacterial strains: 17 isolates were able to inhibit growth of Micrococcus luteus, 4 -Pseudomonas aeruginosa, 2 -Escherichia coli and Bacillus subtilis. In addition, it was determined that two isolates of Pantoea sp. (D_8 and D_10) and Pseudomonas fluorescens group isolate D_7 were able to inhibit growth of the apple scab pathogen (Venturia inaequalis (Cke) Wint.), suggesting a role of the endophytes in disease resistance and a potential use for biocontrol applications.

All plants in nature harbor a diverse community of endophytic bacteria. They can produce a wide range of various compounds, which can positively affect the host plant growth. Endophytes can participate in providing plant with nutrients, competing with plants pathogens or directly effecting the plant growth by synthesis of phytohormones.In this study, endophytic bacteria associated with apple tree buds were isolated, characterized and tested for their ability to produce the plant hormone IAA (indole 3 acetic acid). Nine isolates were shown to produce IAA. Amounts of IAA produced in culture varied between 0.12-0.24 micrograms per milligram of protein. Several bacterial endophytes were shown to produce siderophores and substances which inhibited the growth of the test strain. We also screened the isolates for other PGP traits, as abilities to solubilize phosphate and fix nitrogen. Our results suggest that IAA production and other PGB traits are common among apple tree endophytic bacteria.

Plant-associated bacteria can affect plants in different ways, including plant growth promoting. Beneficial effects on plant growth can be conditioned directly, by providing plants with nutrients -nitrogen, iron or soluble phosphate or by producing plant hormones. Indirect plant growth promotion way is conditioned by the inhibition of growth of pathogenic microorganisms. The surface of plant leaf -phylloplane along to other epiphytic bacterial habitats, is a promising source of microorganisms with plant growth affecting abilities, including those with biotechnological potential.Ability to synthesize indole-3-acetic acid was frequently found among isolates (17 of 19 isolates tested). 13 of the isolates were able to produce siderophores, 10 -solubilize phosphates and 10 were diazotrophs. Isolates J41.1, J41.2 J4a3, J4a4 showed a beneficial effect on pine seedling.