The objectives of this study were to identify and characterize PGPR indigenous to cucumber rhizosphere in Bangladesh, and to evaluate their ability to suppress Phytophthora crown rot in cucumber. Phylogenetic analysis of 16S rRNA sequences identified these isolates as new strains of Pseudomonas stutzeri, Bacillus subtilis, Stenotrophomonas maltophilia, and Bacillus amyloliquefaciens.
Send correspondence Luciane M. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Bacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting Thesis on plant growth promoting rhizobacteria PGPR.
PGPR are highly diverse and in this review we focus on rhizobacteria as biocontrol agents.
Their effects can occur via local antagonism to soil-borne pathogens or by induction of systemic resistance against pathogens throughout the entire plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as siderophores and antibiotics.
Induced systemic resistance ISR in plants resembles pathogen-induced systemic acquired resistance SAR under conditions where the inducing bacteria and the challenging pathogen remain spatially separated. Both types of induced resistance render uninfected plant parts more resistant to pathogens in several plant species.
Rhizobacteria induce resistance through the salicylic acid-dependent SAR pathway, or require jasmonic acid and ethylene perception from the plant for ISR. Rhizobacteria belonging to the genera Pseudomonas and Bacillus are well known for their antagonistic effects and their ability to trigger ISR.
Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for biocontrol strategies to improve cropping systems.
This zone is rich in nutrients when compared with the bulk soil due to the accumulation of a variety of plant exudates, such as amino acids and sugars, providing a rich source of energy and nutrients for bacteria Gray and Smith, This situation is reflected by the number of bacteria that are found around the roots of plants, generally 10 to times higher than that in the bulk soil Weller and Thomashow, The rhizosphere is populated by a diverse range of microorganisms and the bacteria colonizing this habitat are called rhizobacteria Schroth and Hancock, Plant-associated bacteria can be classified into beneficial, deleterious and neutral groups on the basis of their effects on plant growth Dobbelaere et al.
Beneficial free-living soil bacteria are usually referred to as plant growth-promoting rhizobacteria PGPR, Kloepper et al. Independent of the mechanisms of vegetal growth promotion, PGPRs colonize the rhizosphere, the rhizoplane root surfaceor the root itself within radicular tissues Gray and Smith, PGPR affect plant growth in two different ways, indirectly or directly.
The direct promotion of plant growth by PGPR entails either providing the plant with a compound that is synthesized by the bacterium, for example phytohormones, or facilitating the uptake of certain nutrients from the environment Glick, The indirect promotion of plant growth occurs when PGPR lessen or prevent the deleterious effects of one or more phytopathogenic organisms.
This can happen by producing antagonistic substances or by inducing resistance to pathogens Glick, A particular PGPR may affect plant growth and development by using any one, or more, of these mechanisms. PGPR, as biocontrol agents, can act through various mechanisms, regardless of their role in direct growth promotion, such as by known production of auxin phytohormone Patten and Glick,decrease of plant ethylene levels Glick et al.
PGPR and their interactions with plants are exploited commercially Podile and Kishore, and hold great promise for sustainable agriculture. Applications of these associations have been investigated in maize, wheat, oat, barley, peas, canola, soy, potatoes, tomatoes, lentils, radicchio and cucumber Gray and Smith, In this review, we will consider the mechanisms of action of biocontrol agents and describe some successful examples of these rhizobacteria controlling plant diseases.
Microbial Antagonism According to Beattiebacteria that reduce the incidence or severity of plant diseases are often referred to as biocontrol agents whereas those that exhibit antagonistic activity toward a pathogen are defined as antagonists.
The following rhizospheric environment and bacterial antagonistic activities can be highlighted: Siderophores, bacteriocins, and antibiotics production as antagonistic activities The ability of rhizobacteria to produce siderophores and metabolites contributing to antibiosis has been the focus of many studies dedicated to investigating PGPR Maksimov et al.
The uptake of ferric ion via siderophore is largely used by pathogenic and non-pathogenic microorganisms from the soil, human body and marine environments. The importance of siderophore is closely related to iron, which is an essential element for different biological processes Crosa and Walsh, On the other hand, bacteria can produce a wide variety of compounds with antimicrobial activity used as defense systems.
These include broad-spectrum antibiotics, lactic acid produced by lactobacilli, lytic agents such as lysozymes, numerous types of exotoxins and bacteriocins, which also have a bactericidal mode of action Riley and Wertz, Siderophores, bacteriocins and antibiotics are three of the most effective and well known mechanisms that an antagonist can employ to minimize or prevent phytopathogenic proliferation.
Siderophores To satisfy nutritional requirements of iron, microorganisms have evolved highly specific pathways that employ low molecular weight iron chelators termed siderophores.
Siderophores are secreted to solubilize iron from their surrounding environments, forming a complex ferric-siderophore that can move by diffusion and be returned to the cell surface Andrews et al. The active transport system through the membrane begins with the recognition of the ferric-siderophore by specific membrane receptors of Gram-negative and Gram-positive bacteria Boukhalfa and Crumbliss, native plant growth promoting rhizobacteria (PGPR) as potential bio-inoculants for Yerba Mate seedlings.
This thesis has shownthat biomass yields of Yerba Mate seedlings can be increased up to % through bio-inoculation with native PGPR strains.
Interestingly, the biomass yield.
Plant and Soil publishes original papers and review articles exploring the interface of plant biology and soil sciences, and that enhance our mechanistic understanding of plant-soil interactions. This includes both fundamental and. Plant growth-promoting rhizobacteria (PGPR) Rhizobacteria can have deleterious, neutral, or beneficial effects on the host plant (Tuzun and Kloepper , Elliot et al.
). The rhizosphere is the layer of soil that is influenced by the plant root and it has a greater density of organic carbon and bacteria than the. effects on plant growth (Dobbelaereet al., ). Benefi-cial free-living soil bacteria are usually referred to as plant growth-promoting rhizobacteria (PGPR, Kloepper et al., ).
Independent of the mechanisms of vegetal growth promotion, PGPRs colonize the rhizosphere, the rhizo-plane (root surface), or the root itself (within radicular tis-. Assessing the role of native Plant Growth-Promoting Rhizobacteria as bio-inoculants for Yerba Mate (Ilex paraguariensis) PhD thesis submitted to the.
University of Neuchâtel. The Use of Plant Growth-Promoting Rhizobacteria (PGPR) to Improve Plant Growth in Heavy Metal Contaminated Soil for Phytoremediation By Hafeth Fawzi Daraghmeh Supervisor Dr.
Shehdah Jodeh Co-Supervisor Dr. Raed Alkowni This Thesis is submitted in Partial Fulfillment of the Requirements for.