Biocontrol of soilborne plant pathogens

• Published in: The Plant cell Vol. 8; no. 10; pp. 1855 - 1869
• Main Authors: Handelsman, J. (University of Wisconsin, Madison, WI.), Stabb, E.V
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01.10.1996
• Subjects: AGENT PATHOGENE; ANTIBIOTICOS; ANTIBIOTICS; ANTIBIOTIQUE; AUXILIAIRE DE LUTTE BIOLOGIQUE; BACILLUS CEREUS; BIOLOGICAL CONTROL; biological control agents; BIOLOGICAL CONTROL ORGANISMS; BIOSINTESIS; BIOSYNTHESE; BIOSYNTHESIS; CONTROL BIOLOGICO; CONTROL DE ENFERMEDADES; Control of Pathogens; CONTROLE DE MALADIES; DISEASE CONTROL; ENFERMEDADES FUNGOSAS; FONGICIDE; FUNGAL DISEASES; fungal diseases of plants; FUNGICIDAS; FUNGICIDES; FUNGUS CONTROL; GENETICA MOLECULAR; GENETIQUE MOLECULAIRE; GLIOCLADIUM VIRENS; LUTTE BIOLOGIQUE; MALADIE FONGIQUE; Metabolic diseases; Microorganisms; MOLECULAR GENETICS; ORGANISMOS PARA CONTROL BIOLOGICO; ORGANISMOS PATOGENOS; PARASITISM; PARASITISME; PARASITISMO; PATHOGENS; Phytopathology; Plant diseases; plant pathogenic fungi; Plant roots; Plants; PSEUDOMONAS; pseudomonas aureofaciens; Pseudomonas chlororaphis; PSEUDOMONAS FLUORESCENS; Rhizosphere; SIDEROFOROS; SIDEROPHORE; SIDEROPHORES; soil-borne diseases; soilborne diseases; TRICHODERMA; Trichoderma virens
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.8.10.1855

Biocontrol involves harnessing disease-suppressive microorganisms to improve plant health. Disease suppression by biocontrol agents is the sustained manifestation of interactions among the plant, the pathogen, the biocontrol agent, the microbial community on and around the plant, and the physical environment. Even in model laboratory systems, the study of biocontrol involves interactions among a minimum of three organisms. Therefore, despite its potential in agricultural applications, biocontrol is one of the most poorly understood areas of plant-microbe interactions. The complexity of these systems has influenced the acceptance of biocontrol as a means of controlling plant diseases in two ways. First, practical results with biocontrol have been variable. Thus, despite some stunning successes with biocontrol agents in agriculture, there remains a general skepticism born of past failures (Cook and Baker, 1983; Weller, 1988). Second, progress in understanding an entire system has been slow. Recently, however, substantial progress has been made in a number of biocontrol systems through the application of genetic and mathematical approaches that accommodate the complexity. Biocontrol of soilborne diseases is particularly complex because these diseases occur in the dynamic environment at the interface of root and soil known as the rhizosphere, which is defined as the region surrounding a root that is affected by it. The rhizosphere is typified by rapid change, intense microbial activity, and high populations of bacteria compared with non-rhizosphere soil. Plants release metabolically active cells from their roots and deposit as much as 20% of the carbon allocated to roots in the rhizosphere, suggesting a highly evolved relationship between the plant and rhizosphere microorganisms. The rhizosphere is subject to dramatic changes on a short temporal scale-rain events and daytime drought can result in fluctuations in salt concentration, pH, osmotic potential, water potential, and soil particle structure. Over longer temporal scales, the rhizosphere can change due to root growth, interactions with other soil biota, and weathering processes. It is the dynamic nature of the rhizosphere that makes it an interesting setting for the interactions that lead to disease and biocontrol of disease (Rovira, 1965, 1969, 1991; Hawes, 1991; Waisel et al., 1991). The complexity of the root-soil interface must be accommodated in the study of biocontrol, which must involve whole organisms and ultimately entire communities, if we are to understand the essential interactions in soil in the field. The challenge in elucidating mechanisms of biocontrol is in reducing the complexity to address tractable scientific questions. One of the most effective approaches toward the identification of critical variables in a complex system has been genetics. The study of mutants can be conducted in simplified laboratory systems or in the field, thus making accessible the examination of particular genetic changes and the associated biochemical characteristics in the real world. This review presents recent advances in our understanding of the biocontrol of root diseases. We emphasize research aimed at enhancing our understanding of the biology of the interactions that result in disease suppression. It is this understanding that will make possible the practical use of microorganisms in the management of plant disease in agroecosystems. Numerous recent reviews present comprehensively the variety of microbial biocontrol agents (Chet, 1987; Weller, 1988; Whipps and Lumsden, 1991; O'Sullivan and O'Gara, 1992; Cook, 1993; Goldman et al., 1994; Cook et al., 1995; Lumsden et al., 1995). In this discussion of current and future directions in biocontrol, our goal is to present key themes in the discipline, drawing on the bacteria Pseudomonas and Bacillus and the fungi Trichoderma and Gliocladium as examples representing a range of life strategies and mechanisms of disease suppression. We address the principles of interactions of the biocontrol agent with the pathogen, the host plant, and the microbial community, illustrating each principle with some well-studied examples of successful biocontrol agents (DBO).