Biological control ofPythiumspecies

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Abstract
Rapid germination of sporangia of Pythium species in response to seed or root exudates followed by immediate infection, and the ability to cause long‐term root rots make biological control of these pathogens very difficult. Pythium‐suppressive soils exist and these may be good sources of suitable biological control agents. Both bacterial and fungal antagonists are known to affect Pythium species by producing antibiotics, competing for space or nutrients or by direct parasitism. Antagonists have been incorporated into soil or applied to seeds, and, in some instances, control of damping‐off, equivalent to standard fungicide applications, has been achieved. However, reproducible cost‐effective biological control in the field is rare. Nevertheless Pseudomonas fluorescens, Streptomyces griseoviridis, Gliocladium virens, Pythium oligandrum and Trichoderma harzianum have been or are about to be used commercially for the control of diseases caused by Pythium. The problems associated with the commercial acceptance of biological control agents of Pythium are discussed and various methods of improving selection, activity and use are described.