In a laboratory experiment, herbicidal potentials of fungal strains in agricultural soils were investigated. This was with the view of using them to compliment synthetic herbicides which have been associated with adverse effects on the soil ecosystem and thus reduce environmental pollutions while controlling weeds. Soils were collected from four selected farm sites within the Southern Guinea Savanna (SGS) agro ecological zone of Nigeria. Fungi were isolated using the soil dilution method and were identified using their colony and microscopic morphological characteristics. They were screened for their herbicidal properties on the foliages of Amaranthus hybridus using leaf necrosis assay. The percentage frequencies of occurrence of twenty-one fungal isolates were determined. The predominant fungal strains were Aspergillus sydowii (43.47%) and Alternaria alternata (30.43%), Aspergillus tereus (53.85%) and Aspergillus ustus (23.08%), Aspergillus niger (44.44%), Aspergillus tereus (33.33%), Penicillium marneffei (58.06%) and Fusarium vertilliodes (25.81%) in soils from Kogi, Kwara, Niger and Benue farm sites respectively. A very high percentage (80-85%) of all the fungal isolates from the soils showed herbicidal properties. The isolated fungal strains had varying degrees of herbicidal properties. Two fungal strains, Aspergillus fumigatus and Penicillium citrinum had the highest strengths as biocontrol agents as indicated by the large necrotic lesions produced on the foliages of Amaranthus hybridus It was concluded that these two have the potentials for use as bioherbicides. Further investigations were recommended to study the secondary metabolites produced by these fungi and their effects on selected weeds.
Keywords: Bio-herbicide, Soil Fungi, Leaf necrosis assay.