Suppressiveness of organically and conventionally managed soils towards brown foot rot of barley

Five sandy loam soils under organic, integrated and conventional management were chosen to investigate the effect of specific agricultural management practices on suppression of brown foot rot of cereals caused by Fusarium cu lmorum. The relationships between suppressiveness and C and N content of th e soil microbial biomass and microbial activity were investigated. Fungista sis tests and plant bioassays were compared. Differences in suppressiveness were most marked in plant bioassays following seed inoculation with F. cul morum. When inoculum was applied to soil as conidia or mycelia, soil-suppre ssed transmission of the pathogen and disease development. This finding ind icates that the competitive saprophytic ability of the isolate of F, culmor um is poor. The microbial biomass and activity of the soils under organic a nd integrated farming were high. However, high biomass and activity were no t always correlated with high disease suppression. Specific organic amendme nts, such as mulching with straw and the practice of using lucerne as a bre ak-crop in cereal cultivation may influence inoculum potential of F. culmor um, disease outbreak and suppression. The possible significance of soil abi otic factors on disease suppression is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.