Antagonism of Erwinia herbicola towards Leptosphaeria maculans causing blackleg disease of Brassica napus

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Abstract
Phyllosphere micro-organisms of Brassica napus were isolated and their antagonism against Leptosphaeria maculans, causal agent of blackleg disease, was tested in vitro. In paired culture, Erwinia herbicola was found to be highly antagonistic to L. maculans. Bioassay of the culture filtrate of the bacterium against the test fungus revealed that Erw. herbicola secretes an antifungal substance into the culture medium. This substance was partially thermolabile and markedly reduced the germination and germ tube length of L. maculans. Aqueous bacterial suspensions and cold-sterilized culture filtrates, when applied to the seedlings prior to inoculation, significantly reduced the severity of blackleg disease.