Ecological succession and biological control in the phyllosphere
Understanding biological control of plant diseases is dependent on an understanding of succession in microbial communities. The colonization of aboveground plant parts by saprophytic microbes is not well understood, but it appears to follow the same model as that in soil communities. When a nutrient source is added, such as plant debris, there is a succession of organisms organized along a spectrum of complexity of carbohydrate utilization. A similar phenomenon may occur during the colonization of plant parts newly exposed by natural development or by wounds, upon which many pathogens depend to serve as sites of infection. These nutrient utilization strategies have been interpreted as indicative of r (rapidly utilizing simple sugars) and K (slowly utilizing lignin) life strategies. If the concepts of r and K species are applicable to microbes, it could indicate what type of interaction would be most likely to be successful for biological control. For example, pathogens that are r species may be better controlled by competition, and K pathogenic species better controlled by parasitism. However, for any interaction to take place, the control agent's environmental requirements, both biotic and abiotic, must overlap with that of the pathogen. The concepts of ecological succession and r and K species, if appropriate for microorganisms, may prove very valuable when developing biological control strategies. Key words: antibioses, competition, island biogeography, parasitism.