Induction of systemic resistance of tobacco to tobacco necrosis virus by the root-colonizing Pseudomonas fluorescens strain CHA0: influence of the gacA gene and of pyoverdine production
TL;DR: Plants tested showed resistance in leaves to infection with tobacco necrosis virus to the same extent as plants previously immunized with TNY (induced resistance control) and Pseudomonas fluorescens strain CHA0, which suppresses various plant diseases caused by soilborne pathogens also can restrict leaf disease.
Abstract: Pseudomonas fluorescens strain CHA0, which suppresses various plant diseases caused by soilborne pathogens, also can restrict leaf disease. Plants of Nicotiana glutinosa and of two cultivars of N. tabacum were grown in autoclaved natural soil previously inoculated with strain CHA0. After 6 wk, all the plants tested showed resistance in leaves to infection with tobacco necrosis virus (TNV) to the same extent as plants previously immunized with TNV (induced resistance control). Polyacrylamide gel electrophoresis and enzyme assays showed that the same amount of PR proteins (Pr-1 group proteins, beta-1,3-glucanases, and endochitinases) was induced in the intercellular fluid of leaves of plants grown in the presence of strain CHA0 as in the intercellular fluid of leaves of plants immunized by a previous TNV inoculation on a lower leaf. Strain CHA0 was reisolated from the roots but could not be detected in stems or leaves. Strain CHA96, a gacA (global activator)-negative mutant of strain CHA0 defective in the production of antibiotics and in the suppression of black root rot of tobacco, had the same capacity to induce PR proteins and resistance against TNV as did the wild-type strain. CHA400, a pyoverdine-negative mutant of strain CHA0 with the same capacity to suppress black root rot of tobacco and take-all of wheat as the wild-type strain, was able to induce PR proteins but only partial resistance against TNV. P3, another P. fluorescens wild-type strain, does not suppress diseases caused by soilborne pathogens and induced neither resistance nor PR proteins in tobacco leaves. Root colonization of tobacco plants with strain CHA0 and its derivatives as well as leaf infection with TNV caused an increase in salicylic acid in leaves. These results show that colonization of tobacco roots by strain CHA0 reduces TNV leaf necrosis and induces physiological changes in the plant to the same extent as does induction of systemic resistance by leaf inoculation with TNV
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TL;DR: As agricultural production intensified over the past few decades, producers became more and more dependent on agrochemicals as a relatively reliable method of crop production.
Abstract: Pathogenic microorganisms affecting plant health are a major and chronic threat to food production and ecosystem stability worldwide As agricultural production intensified over the past few decades, producers became more and more dependent on agrochemicals as a relatively reliable method of crop
2,246 citations
Cites background from "Induction of systemic resistance of..."
...Biochemical or physiological changes in plants (139) include induced accumulation of pathogenesis-related proteins (PR proteins) such as PR-1, PR-2, chitinases, and some peroxidases (76, 100, 109, 126, 139, 182)....
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TL;DR: Rhizobacteria-mediated induced systemic resistance (ISR) is effective under field conditions and offers a natural mechanism for biological control of plant disease.
Abstract: Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.
2,146 citations
TL;DR: Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocOntrol agents used singly.
Abstract: The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.
1,818 citations
TL;DR: The main functions of rhizosphere microorganisms and how they impact on health and disease are reviewed and several strategies to redirect or reshape the rhizospheric microbiome in favor of microorganisms that are beneficial to plant growth and health are highlighted.
Abstract: Microbial communities play a pivotal role in the functioning of plants by influencing their physiology and development. While many members of the rhizosphere microbiome are beneficial to plant growth, also plant pathogenic microorganisms colonize the rhizosphere striving to break through the protective microbial shield and to overcome the innate plant defense mechanisms in order to cause disease. A third group of microorganisms that can be found in the rhizosphere are the true and opportunistic human pathogenic bacteria, which can be carried on or in plant tissue and may cause disease when introduced into debilitated humans. Although the importance of the rhizosphere microbiome for plant growth has been widely recognized, for the vast majority of rhizosphere microorganisms no knowledge exists. To enhance plant growth and health, it is essential to know which microorganism is present in the rhizosphere microbiome and what they are doing. Here, we review the main functions of rhizosphere microorganisms and how they impact on health and disease. We discuss the mechanisms involved in the multitrophic interactions and chemical dialogues that occur in the rhizosphere. Finally, we highlight several strategies to redirect or reshape the rhizosphere microbiome in favor of microorganisms that are beneficial to plant growth and health.
1,752 citations
Cites background from "Induction of systemic resistance of..."
...However, some bacterial strains do not induce systemic resistance via the JA/ET pathway but via the salicylic acid (SA)-pathway (Maurhofer et al., 1994; De Meyer and Höfte, 1997; Maurhofer et al., 1998; De Meyer et al., 1999; Audenaert et al., 2002; Barriuso et al., 2008; Van de Mortel et al. 2012)....
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TL;DR: This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms, and mechanisms involved in the tripartite interactions between beneficialmicroorganisms, pathogens and the plant.
Abstract: The rhizosphere is a hot spot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities. The rhizosphere harbors many organisms that have a neutral effect on the plant, but also attracts organisms that exert deleterious or beneficial effects on the plant. Microorganisms that adversely affect plant growth and health are the pathogenic fungi, oomycetes, bacteria and nematodes. Most of the soilborne pathogens are adapted to grow and survive in the bulk soil, but the rhizosphere is the playground and infection court where the pathogen establishes a parasitic relationship with the plant. The rhizosphere is also a battlefield where the complex rhizosphere community, both microflora and microfauna, interact with pathogens and influence the outcome of pathogen infection. A wide range of microorganisms are beneficial to the plant and include nitrogen-fixing bacteria, endo- and ectomycorrhizal fungi, and plant growth-promoting bacteria and fungi. This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms. Specific attention is given to mechanisms involved in the tripartite interactions between beneficial microorganisms, pathogens and the plant. We also discuss how agricultural practices affect pathogen and antagonist populations and how these practices can be adopted to promote plant growth and health.
1,370 citations
Cites background from "Induction of systemic resistance of..."
...2004), the siderophore pyoverdine (Maurhofer et al. 1994), DAPG (Iavicoli et al....
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