Characterization of an antifungal soil bacterium and its antagonistic activities against Fusarium species

Bacteria were isolated from a cultivated soil and screened for antagonistic activity against Fusarium graminearum, a predominant agent of ear rot and head blight in cereal crops. Based on its in vitro effectiveness, isolate D1/2 was selected for characterization and identified as a strain of Bacillus subtilis by phenotypic tests and comparative analysis of its 16S ribosomal RNA gene (rDNA) sequence. It inhibited the mycelial growth of a collection of common fungal phytopathogens, including eight Fusarium species, three other ascomycetes, and one basidiomycete. The cell-free culture filtrate of D1/2 at different dilutions was active against macroconidium germination and hyphal growth of F. graminearum, depending on the initial macroconidium density. It induced the formation of swollen hyphal cells in liquid cultures of this fungus grown from macroconidia. A bioassay also demonstrated that D1/2 offered in planta protection against the damping-off disease in alfalfa seedlings caused by E graminearum, while the type strain of B. subtilis was ineffective. Hence, B. subtilis D1/2 or its culture filtrate has potential application in controlling plant diseases caused by Fusarium.