Getting the best from pot trials with soil-borne Oomycetes

Abstract

Soil-borne Oomycetes are important pathogens of nursery plants, agricultural and horticultural crops, and woody plants in natural ecosystems. They are most damaging when plants are overwatered or growing in poorly drained sites. Poor growth could result from root infection, root damage resulting from the anoxic conditions which develop in saturated soil, or both. This is essential information for devising appropriate management options, as these will differ depending on the primary cause of poor health. Pot experiments are often used to determine whether these soil-borne pathogens cause root infection which is assumed to be by zoospores produced in wet soil. Soil saturation followed by draining, is included as part of the experimental protocol to generate zoospores from the inoculum and facilitate their movement to, and infection of, plant roots. However, if soil saturation persists until the soil becomes anoxic, this may affect the host. In our opinion, this can muddle the interpretation of results, unless there are adequate controls which include root infection in unsaturated soil, and the effect of soil saturation on the host in the absence of the pathogen. Pot experiments are expensive in both time and equipment. They must be conducted to provide clear answers to the postulated hypotheses and ensure experiments are repeatable. We provide guidelines for conducting such pot experiments which will assist in clarifying the roles of these pathogens and soil saturation on plant growth, both separately and in combination.