Submitted to: Proceedings of the International Workshop on Implementation of biocontrol in Practice in Temperate Regions-Present and Near Future
Publication Type: Proceedings
Publication Acceptance Date: 11/25/2005
Publication Date: 4/3/2006
Citation: Linderman, R.G. 2006. Biocontrol in the mycorrhizosphere. Proceedings of the International Workshop on Implementation of biocontrol in Practice in Temperate Regions-Present and Near Future. p.137. Interpretive Summary: Biological control is an emerging strategy for the management of plant diseases in production agriculture. Management of soilborne diseases is especially difficult due to the lack of other options such as chemicals. Soil fumigation is practiced in some cases, but the number of fumigants, such as methyl bromide, is decreasing. The workshop in Denmark focused on biocontrol of insects and diseases, and this paper was an invited keynote address that specifically focused on research done on the role of mycorrhizae in the biological control of soilborne diseases. The research reported was the first to indicate and present data on the stimulation of antagonistic bacteria in association with the roots and hyphae of mycorrhizal plants, and these results could account for the greater resistance of plants with mycorrhizae than those without. This research was presented as cutting edge and was appreciated by the participants as such.
Technical Abstract: The mycorrhizal association of fungi with the roots of plants in natural, undisturbed ecosystems logically includes associations with other functional groups of soil microbes that contribute to successful plant growth and health in what is called the “mycorrhizosphere”. Mycorrhizosphere bacterial populations can change dynamically over time and are influenced by what microbes are present in the background soil or growth medium, and by the process of selective enrichment of specific functional groups of microbes from that medium due to root exudation and arbuscular mycorrhizal (AM) fungus hyphal exudates. The mycorrhizosphere phenomenon includes specific roles that some rhizobacteria might play in combination with mycorrhizal fungi, especially in relation to plant growth enhancement and increased antagonism against soilborne pathogens. Disease suppressive soils occur naturally, and mycorrhizae play a significant role in them. We have determined that AM formation causes an increase in levels of antagonistic bacteria, provided the background soil contains effective antagonists to be selectively increased. This has led me to describe a new mycorrhizosphere paradigm that is a microbial hierarchy wherein roots attract mycorrhizal fungi and the latter attract bacterial associates. Optimization of any production system comes from having microbes, such as bacterial antagonists, selected from a medium with high microbial diversity, that are efficacious and compatible and therefore can function in tandem in this mycorrhizosphere paradigm involving plants forming AM that select specific antagonistic bacterial associates.