Indigenous Putative Nitrogen-Fixing Bacteria from Northern Kazakhstan: Antagonistic Activity and Growth Promotion in Buckwheat

The present study aimed to evaluate the biocontrol and plant growth-promoting potential of putative nitrogen-fixing bacterial strains isolated from the soils of Northern Kazakhstan against major cereal crop phytopathogens and during the early stages of plant development. Phytopathogenic fungi, Fusarium proliferatum and Alternaria alternata, were isolated from infected cereal tissues and seeds using conventional mycological techniques. The antagonistic activity of the bacterial strains was assessed using a dual-culture assay. A total of 26 bacterial isolates were screened for antagonistic activity and plant growth-promoting effects. Several isolates exhibited pronounced inhibitory activity against both pathogens by suppressing fungal mycelial growth. The plant growth-promoting potential of bacterial culture filtrates was evaluated under in vitro conditions using buckwheat (Fagopyrum esculentum Moench) varieties ‘Shortandinskaya 6’ and ‘Shortandinskaya Krupnozernaya’. Germination energy, laboratory germination, shoot length, and root length were recorded during seedling development. The tested bacterial culture filtrates showed a stimulatory effect on seedling growth, with the most pronounced response observed in root elongation, indicating their positive influence on rhizogenesis. The obtained results demonstrate that Agrobacterium pusense st.51S, Ensifer fredii st.59S, and Oricola cellulosilytica st.70S exhibited strong antagonistic activity against Fusarium proliferatum, whereas O. cellulosilytica st.70S, Streptomyces virginiae st.11S, and Ensifer meliloti st.56S effectively inhibited the growth of Alternaria alternata. In addition, E. meliloti st.56S, Priestia megaterium st.35S, Rhizobium giardinii st.2S, and Ensifer sp. st.91S significantly promoted buckwheat seed germination and seedling growth. The most pronounced growth-promoting effect was observed for E. meliloti st.56S, which increased shoot and root length of ‘Shortandinskaya 6’ by 31.4% and 23.8%, respectively, compared with the control. These strains represent promising candidates for the development of microbial bioformulations aimed at improving seed quality, enhancing early plant development, and promoting sustainable crop production under the dry steppe conditions of Northern Kazakhstan.