Studies on soil fumigation—IV: Effects on fungi

Abstract

The effect of soil fumigation with a chloropicrin-methyl bromide mixture(1:1) at 440 kg·ha −1 on the fungal flora of a wheat-field has been investigated. Recolonization of fumigated soil and the occurrence of fungi on roots of wheat growing in fumigated and untreated soil were also followed. Very few fungi survived in fumigated soil that had been covered with polythene sheeting, but in uncovered fumigated soil some fungi survived especially at or near the soil surface. Study of recolonization of covered fumigated soil showed that some fungi, notably species of Chaetomium and Mortierella, appeared to survive fumigation and then increase in number, but many of the fungi recolonizing surface soil (2.5 cm), Alternaria, Stemphylium, Mucor, Cladosporium, Epicoccum), appeared to have come from the air. Recolonization of surface soil was not uniform; high counts were often due to the spores of one or a few fungi and samples collected a few cm apart might show different fungi in high number. In subsurface soil (5–22.5 cm) recolonization was much slower and even 117 days after fumigation the number of colonies and species of fungi was low compared with untreated soil. The common fungi on roots of plants grown in uncovered fumigated or untreated soil were very similar though initially there were fewer fungi on roots from fumigated soil. The main differences recorded were that Chaetomium species were more frequent on roots from fumigated soil and that. in general, Cylindrocarpon destruetans, Embellisia chlamydospora, species of Pythium and Rhizoctonia, and Gaeumannomyces graminis were more common on roots in untreated soil.