Isolation, Molecular Identification, and Biocontrol Evaluation of Indigenous Fungi from Iraqi Agricultural Soils against Soil-Borne Plant Pathogens

Abstract

Background: The increasing incidence of fungal diseases in Iraqi agricultural systems highlights the need for environmentally sustainable alternatives to conventional chemical fungicides. Native fungal isolates may offer advantages under local environmental conditions, including high temperature, alkaline pH, and salinity, and may provide potential sources of biological control agents. Objectives: This study aimed to isolate and molecularly characterize native fungi from rhizosphere soils collected from three Iraqi governorates, evaluate their in vitro antagonistic activity against common soil-borne fungal pathogens using dual-culture assays, characterize selected extracellular enzyme activities, including chitinase, cellulase, and protease, and assess their biocontrol effectiveness and plant growth-promoting potential under greenhouse conditions. Methods: A total of forty-seven fungal colonies were isolated from rhizosphere soils collected in Baghdad, Babylon, and Diyala during May–June 2025. Based on preliminary mycelial growth inhibition percentage (MGIP ≥40%), three isolates—Trichoderma harzianum F1, Aspergillus niger F2, and Penicillium chrysogenum F3—were selected and molecularly identified by ITS rDNA sequencing, with ≥98.9% similarity using NCBI BLAST. Dual-culture assays were used to evaluate MGIP against Fusarium oxysporum f. sp. lycopersici, Rhizoctonia solani, and Alternaria alternata. Selected enzyme activities and greenhouse biocontrol and plant growth-promoting effects were subsequently evaluated. Results: T. harzianum F1 demonstrated the highest MGIP (69.3–78.4%) and the greatest chitinase activity (4.80±0.32 U/mL at 96 h). Under greenhouse conditions, T. harzianum F1 reduced the disease severity index by 65.3% and outperformed the controls across all evaluated vegetative growth parameters. Conclusions: T. harzianum F1 demonstrated strong antagonistic activity against the tested soil-borne fungal pathogens, substantial chitinase activity, and favorable biocontrol and plant growth-promoting effects under greenhouse conditions. These findings support its potential as a locally derived biocontrol agent for managing soil-borne fungal diseases in Iraqi agricultural systems. Further field-scale validation, formulation studies, and mechanistic investigations are required before its practical application as a biopesticide.