Biological control of wheat root rot using rhizosphere isolates of Bacillus sp. and Trichoderma harzianum
Abstract Soil-borne fungal pathogens significantly limit wheat production in Kazakhstan, particularly Fusarium solani (Mart.) Sacc. 1881 and Bipolaris sorokiniana (Sacc.) Shoemaker, 1959, which cause root rot and early seedling decline. This study aimed to isolate and characterize indigenous rhizosphere antagonists with biocontrol potential against these pathogens and to evaluate their effects on wheat seed germination and early growth. More than 20 microbial isolates were obtained from the rhizosphere of winter wheat. Two active antagonistic strains were selected by dual-culture assays: Bacillus sp. NK1 and Trichoderma harzianum S1. Inhibition zones against F. solani reached 23.75 ± 0.67 mm for NK1 and 32.89 ± 0.67 mm for S1. Cell-free culture supernatants significantly reduced mycelial growth and completely inhibited spore germination. Molecular identification based on 16S rRNA sequencing and TEF-1α/RPB2 analysis confirmed the taxonomic affiliation of both isolates. Seed treatment significantly improved germination (88%), root length, shoot length, and seedling vigor compared with untreated controls (P < 0.01). In pot experiments, both strains promoted biomass accumulation and improved seedling growth under pathogen pressure, with the Bacillus strain showing the strongest growth-promoting effect. Combined inoculation did not result in a synergistic response. These findings highlight the potential of indigenous rhizosphere microorganisms as biological control agents for the management of wheat root rot pathogens.