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

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Abstract:

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 F. 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.Key words: antifungal activity, Bacillus subtilis, biological control, biopesticide, Fusarium species.

Nous avons isolé des bactéries d'un sol en culture et avons criblé leur activité antagoniste contre Fusarium graminearum, un des principaux agents de la pourriture des épis et du flétrissement des plantules de céréales. À la lumière de son efficacité in vitro, nous avons sélectionné l'isolat D1/2 afin de la caractériser et l'avons identifié comme étant une souche de Bacillus subtilis grâce à des tests phénotypiques et à des analyses comparatives de la séquence de son gène d'ARN ribosomal 16S (ADNr). Cette souche a inhibé la croissance des mycéliums d'une collection de champignons phytopathogènes communs incluant huit espèces de Fusarium, trois autres ascomycètes et un basidiomycète. Un filtrat de culture acellulaire de D1/2 à différentes dilutions a agit contre la germination de macrogonidies et la croissance d'hyphes de F. graminearum, selon la densité de macrogonidies de départ. Il a induit la formation de cellules hyphales gonflées dans des cultures liquides de ce champignon produites à partir de macrogonidies. Un bioessai a également démontré que D1/2 fournissait une protection in planta contre la fonte des semis occasionné par F. graminearum se retrouvant dans les semis de luzerne, alors que la souche type de B. subtilis fut inefficace. Ainsi, la souche D1/2 de B. subtilis ou son filtrat de culture pourrait être utilisée pour combattre les maladies de plantes causées par Fusarium.Mots clés : activité antifongique, Bacillus subtilis, lutte biologique, biopesticide, espèces de Fusarium.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2003

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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