Soilborne plant diseases caused by Pythium spp: Ecology, epidemiology, andprospects for biological control

Soilborne root diseases caused by plant pathogenic Pythium species cause se rious losses in a number of agricultural production systems, which has led to a considerable effort devoted to the development of biological agents fo r disease control. In this article we review information on the ecology and biological control of these pathogens with the premise that a clear unders tanding of the ecology of the pathogen will assist in the development of ef ficacious biocontrol agents. The lifecycles of the pathogens and etiology o f hose infection also are reviewed, as are epidemiological concepts of inoc ulum-disease relationships and the influence of environmental factors on pa thogen aggressiveness and host susceptibility. A number of fungal and bacte rial biocontrol agents are discussed and parallels between their ecology an d that of the target pathogens highlighted. The mechanisms by which these m icrobial agents suppress diseases caused by Pythium spp., such as interfere nce with pathogen survival, disruption of the process of plant infection, a nd induced host resistance, are evaluated. The possibilities for enhancemen t of efficacy of specific biological control agents by genetic manipulation or deployment tactics are discussed, as are conceptual suggestions for con sideration when developing screening programs for antagonists.