Ecological Interactions and Biological Control

Linda L. Kinkel and Steven E. Lindow

Competitive interactions among microbes on plant surfaces can influence disease development, and considerable efforts are now concentrated towards increasing the effectiveness of resource competition in reducing pathogen populations and disease. The practical use of competition as a strategy for biocontrol, however, is still very limited. A number of factors constrain the effective use of competition in biocontrol: (1) a lack of efficient or relevant strategies for screening effective competitors, (2) a limited understanding of the diversity and specificity of competitive interactions among epiphytic microbial populations, and (3) an absence of data on the habitat conditions under which competitive interactions may be most intense. In this chapter, we will review briefly systems in which competitive interactions are important in disease biocontrol. Pseudomonas syringae is used as a model to consider the types of ecological information needed to enhance competition-based biocontrol.

Competition between coexisting populations can be broken down into at least two distinct categories ( Roughgarden 1979): competition for limiting resources (exploitative competition); and interaction through some form of physical or chemical attack (interference competition) ( Arthur 1987). In addition, apparent competition, in which members of coexisting species appear to be negatively influenced by one another, can result from the activities of a predator consuming members of both coexisting populations ( Arthur 1987). In biological control, interference competition is commonly the result of the production by microbial antagonists of antibiotics effective in inhibiting the pathogen population. This topic is addressed in Milner et al. (Chapter 6, in this volume). Even in cases where antibiotic production is the major mechanism by which pathogen populations and disease development are reduced, however, exploitative competitive ability may influence the outcome of the interaction (Handels

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