Deep insight into compositional and functional features of endophytic bacterial communities residing in wheat grains opens the way to the use of their plant growth promoting and biocontrol abilities in agricultural biotechnology. The aim of this work was to compare grain-residing endophytes from winter wheat varieties with different sensitivity to Pseudomonas syringae pv. atrofaciens (McCulloch) and to examine their plant-beneficial traits and antagonistic effects. Grain-residing bacteria were isolated from surface-sterilized grains of three wheat varieties sown in Ukraine following a culture-dependent protocol, and were screened for their plant growth promotion (PGP) and antagonistic properties. Bacterial morphotypes were represented by gram-negative rods, endospore-forming bacilli and gram-positive cocci. Different resistance to phytopathogenic pseudomonads was associated with distinctive quantitative and functional features of grain-residing endophytic communities. High resistance to P. syringae was coupled with the prevalence of gram-negative rods in the endophytic community, the highest proportion of endophytic bacteria possessing three PGP activities (phosphate solubilization, nitrogen fixation and production of indolic compounds) simultaneously, and with the most potent antagonistic activity of grain-residing endospore-forming bacilli. In total, five grain-residing isolates, which were obtained from three wheat varieties (two isolates from varieties with medium and high resistance and one – from a low-resistant variety), demonstrated ability to restrain P. syringae pv. atrofaciens (McCulloch) growth. Two isolates (P6 and P10) which were obtained from the high-resistant wheat variety Podolyanka and were assigned to Paenibacillus and Brevibacillus genera according to their biochemical profiling and MS-DS identification, showed the most potent antagonistic effects as indicated by maximum inhibition zone in agar well diffusion assay. These results shed light on the association of the features of grain-residing endophytic bacteria with wheat resistance to phytopathogenic pseudomonads. Isolates from the high-resistant wheat variety can be recommended for grain dressing as plant growth promoting and biocontrol agents for P. syringae pv. atrofaciens (McCulloch).

Pseudomonas syringae, the causal agent of basal bacteriosis of wheat, is the most dangerous wheat pathogen in Ukraine. The phytopathogen affects all parts of plants and seeds, and may be the cause of their low germination. It also causes empty-head leading to crop losses and quality decrease. P syringiae survives on host plant residues, in soil and on seed. Seed infestation can play an important role in disease epidemiology. An important component of the outer membrane and the virulence factor of phytopathogenic bacteria of the genus Pseudomonas is lipopolysaccharide (LPS), which participates in pathogenesis processes, and is responsible for toxigenicity and immunogenicity of causal agents. The strategic importance of wheat in the agrarian market of Ukraine actualizes the research into the varieties resistant to basal bacteriosis. The study aims to determine the effects of phytopathogenic bacteria Pseudomonas syringae pv. coronafaciens and P. syrіngae pv. atrofaciens, as well as their LPS on seeds of different wheat varieties. Bacterial strains were obtained from the collection of live cultures at the department of phytopathogenic bacteria of D. K. Zabolotny Institute of Microbiology and Virology of the NASU. To conduct the experiment a suspension of living cells of the pathogen with a concentration of 109 CFU / ml and LPS solution at the concentration of 5 mg/ml was used. Exposure time was 24 h. The seed germination and the length of the main root of the sprout were determined after 4 days of germination period. Phytotoxic effect of P. syrіngae cells and their LPS was investigated using two varieties of winter wheat (Discus and Huculus) and spring wheat variety of Grenny. Introduced in Ukraine wheat varieties of foreign breeding Discus, Hukulus and Grenny were characterized by moderate sensitivity to phytopathogenic bacteria P. syrinae pv. coronafaciens and P. syrіngae pv. atrofaciens, as well as to their LPS. The most resistant to the phytopathogenic effect of P. syrіngae pathovars were the grains of the variety of winter wheat Discus. Live bacterial suspensions exerted a more pronounced phytotoxic effect, compared to their LPS, towards wheat grains of winter varieties and less pronounced than LPS - towards grain of spring wheat variety.