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Integrating soil sterilisation with the application of biocontrol agents

Professor John Whipps

Applying selected biocontrol agents to steam sterilised soil where the natural microbial balance has been disrupted, is an integrated control method that may delay re-invasion by plant pathogenic organisms. However, it is important to understand the survival and behaviour of any biocontrol agents that are artificially introduced to the soil, to determine their effectiveness in a disturbed environment.

Two selected biocontrol agents were used in this work, Coniothyrium minitans (a mycoparasite of Sclerotinia sclerotiorum), and Bacillus subtilis MBI 600 (a bacterium antagonistic to pathogens causing damping-off diseases). These biocontrol agents were separately added to completely sterilised, pasteurised and non-sterile soil samples, and their survival monitored over 30 days. Results from these experiments showed good survival for C. minitans in sterilised, pasteurised and non-sterile soil when added at a rate of 1 x 106 cfu g-1 soil, and good survival in sterilised and pasteurised soil when added at a rate of 1 x 103 cfu g-1 soil. B. subtilis MBI 600 survived well and increased in number in sterilised soil, forming spores at a high rate. Although no increase in numbers was seen in pasteurised or non-sterile soil and spores were generally formed at low levels, the final numbers of B. subtilis MBI 600 spores were higher in pasteurised than non-sterile soil.

Survivial of coniothryium minitans in soil

Survival of C. minitans in soil

Both biocontrol agents clearly have the potential to survive well in pasteurised soil, and experiments are underway to determine their ability to control their target pathogens under these conditions.

Funding: HortLINK

Collaborators: Aberdeen University and University of Newcastle-upon-Tyne

Sponsors: Bioquell Food Ltd.; Berry World Ltd; Defra; East Malling Trust for Horticultural Research; Greenvale AP; HDC; Langmead Farms Ltd; Becker Underwood UK; REGERO SA; Tesco Stores Ltd and TIO Ltd.

This article first appeared in the HRI Annual Report (2002-2003)

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