Biological Control of Soilborne Plant Diseases

Biological control, the practice of managing the population of one organism to reduce the population of another, unwanted organism, is thought to have been applied to agricultural systems as early as 2000 years ago to control plant insect pests. Industry improvements including reduced production costs, better quality control, distribution and release methods, and more complete guidance for farmers have further stimulated acceptance among growers, as have the increased cost of conventional pesticides, the insurgence of pest resistance, and demonstrated evidence of effective performance by biologicals. The rhizosphere, the thin layer of soil adjacent to and influenced by terrestrial plant roots, is host to a complex assemblage of commensal, mutualistic, or pathogenic fungi, bacteria, and archaea. Colonization is a dynamic process governed by microbial determinants as well as those of the host plant, including hormone-regulated local and systemic defense mechanisms.