Erwinia herbicolaas a Biocontrol Agent ofFusarium culmorumandPuccinia reconditaf. sp.triticion Wheat

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Abstract
Antibiotic-producing microorganisms (15 bacteria and 54 actinomycetes) were isolated from the rhizosphere and rhizoplane of Gramineae species. Their in vitro activity against Fusarium culmorum was correlated with their ability to suppress the soilborne pathogen on wheat seedlings in the greenhouse after seed coating. At least 40% disease suppression was caused by 22% of the strains. Seed treatment with one of the most active strains, Erwinia herbicola B247, resulted in about 90% disease suppression, detected by enzyme-linked immunosorbent assay, even with high pathogen inoculum concentrations in the soil (104-105 cfu/g). The antagonist spread from the treated seed onto the root and shoot, although population densities declined with time and distance from the seed. An antibiosis-negative Tn5 mutant of E. herbicola still suppressed f. culmorum in vivo to some extent, suggesting that mechanisms other than antibiosis also are involved in disease reduction. The antagonist E. herbicola B247 also was suppressive to Puccinia recondita f. sp. tritici on wheat leaves. In this case, antibiosis was the mechanism of control, because the Tn5 mutant was inactive, and nearly complete protection was attained by application of cultural filtrate from the wild-type bacterium.