The effect of fumigants on soil recolonization in the glasshouse by organisms colonizing the spermosphere

Abstract

SUMMARYGerminating turnip seeds were used as baits to measure changes in colonizing floras of the spermosphere in glasshouse soil boxes following fumigation. The spermosphere mycoflora of the untreated soil was always dominated by Fusarium, Pythium, and Gliocladium spp. Methyl bromide, chloropicrin, and MBC33 (a 67:33 mixture of methyl bromide and chloropicrin), applied in polyethylene bags at a rate of 2·5 ml/cubic foot of soil, greatly reduced colonization by Fusarium and Pythium spp. for 120 days. Fungi and actinomycetes recolonizing treated soils were more active than in untreated soils, and each fumigant induced a characteristic recolonization pattern. The spermosphere of methyl bromide‐treated soil was initially dominated by actinomycetes and later by Penicillium spp. In chloropicrin‐treated soil, Trichoderma and later Penicillium spp. dominated, and in soil treated with MBC 33, Penicillium and Trichoderma spp. were co‐dominant. Dilution plates, made at the same time from the same soil, indicated a close correlation between inoculum density of different fungi in the soil and their inoculum potentials towards the spermosphere.