, Volume 25, Issue 1, pp 129-142

The effects of micro-organisms upon plant growth

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Phytotoxins developed during heat-sterilization of soil were removed by 40 per cent of the fungi and ten per cent of the bacteria isolated from inoculated heat-sterilized soil. Detoxication by the fungi was not necessarily associated with marked proliferation in sterile soil,Trichoderma viride was an active colonizer of sterile soil but quite ineffective as a detoxicating agent.

The phytotoxins could be readily leached out and their effects transmitted to sterile sand and irradiated soil. Results indicate that the toxicity is not due to changes in pH, soluble manganese or ammonia but is probably due to the formation of toxic organic materials.

Primary root growth of subterranean clover is markedly stunted by toxins formed during heat-sterilization of soil and could provide an extremely sensitive bioassay for toxicity.

Detoxication by micro-organisms may have been misinterpreted in the past as a direct stimulation of plant growth and caution is required in studies of the effects of micro-organisms upon plant growth.