Screening siderophore producing bacteria as potential biological control agent for fungal rice pathogens in Thailand
30 Jun 2009-World Journal of Microbiology & Biotechnology (Springer Netherlands)-Vol. 25, Iss: 11, pp 1919-1928
TL;DR: The study demonstrated antagonistic activity towards the target pathogens discussed and are thus potential agents for biocontrol of soil borne diseases of rice in Thailand and other countries.
Abstract: Rice (Oryza sativa) is a staple food in Thailand and, in addition, feeds around one half of the world’s population. Therefore, diseases of rice are of special concern. Rice is destroyed by 2 main pathogens, Fusarium oxysporum and Pyricularia oryzae the causative agents of root rot and blast in rice respectively. These pathogens result in low grain yield in Thailand and other Southeast Asian countries. Soil samples were taken from paddy fields in Northern Thailand and bacteria were isolated using the soil dilution plate method on Nutrient agar. Isolation yielded 216 bacterial isolates which were subsequently tested for their siderophore production and effectiveness in inhibiting mycelial growth in vitro of the rice pathogenic fungi; Alternaria sp., Fusarium oxysporum, Pyricularia oryzae and Sclerotium sp., the causal agent of leaf spot, root rot, blast and stem rot in rice. It was found that 23% of the bacteria isolated produced siderophore on solid plating medium and liquid medium, In dual culture technique, the siderophore producing rhizobacteria showed a strong antagonistic effect against the Alternaria (35.4%), Fusarium oxysporum (37.5%), Pyricularia oryzae (31.2%) and Sclerotium sp. (10.4%) strains tested. Streptomyces sp. strain A 130 and Pseudomonas sp. strain MW 2.6 in particular showed a significant higher antagonistic effect against Alternaria sp. while Ochrobactrum anthropi D 5.2 exhibited a good antagonistic effect against F. oxysporum. Bacillus firmus D 4.1 inhibited P. oryzae and Kocuria rhizophila 4(2.1.1) strongly inhibited Sclerotium sp. P. aureofaciens AR 1 was the best siderophore producer overall and secreted hydroxamate type siderophore. This strain exhibits an in vitro antagonistic effect against Alternaria sp., F. oxysporum and P. oryzae. Siderophore production in this isolate was maximal after 15 days and at an optimal temperature of 30°C, yielding 99.96 ± 0.46 μg ml−1 of siderophore. The most effective isolates were identified by biochemical tests and molecular techniques as members of the Genus Bacillus, Pseudomonas and Kocuria including B. firmus D 4.1, P. aureofaciens AR1 and Kocuria rhizophila 4(2.1.1). The study demonstrated antagonistic activity towards the target pathogens discussed and are thus potential agents for biocontrol of soil borne diseases of rice in Thailand and other countries.
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TL;DR: Two related alternatives are conjecture to explain the improved plant performance under biochar treatment: the biochar stimulated shifts in microbial populations towards beneficial plant growth promoting rhizobacteria or fungi, and low doses of biochar chemicals, many of which are phytotoxic or biocidal at high concentrations, stimulated plant growth at low doses (hormesis).
Abstract: The impact of additions (1–5% by weight) of a nutrient-poor, wood-derived biochar on pepper (Capsicum annuum L.) and tomato (Lycopersicum esculentum Mill.) plant development and productivity in a coconut fiber:tuff growing mix under optimal fertigation conditions was examined. Pepper plant development in the biochar-treated pots was significantly enhanced as compared with the unamended controls. This was reflected by a system-wide increase in most measured plant parameters: leaf area, canopy dry weight, number of nodes, and yields of buds, flowers and fruit. In addition to the observed increases in plant growth and productivity, the rhizosphere of biochar-amended pepper plants had significantly greater abundances of culturable microbes belonging to prominent soil-associated groups. Phylogenetic characterization of unique bacterial isolates based on 16S rRNA gene analysis demonstrated that of the 20 unique identified isolates from roots and bulk soil from the char-amended growing mix, 16 were affiliated with previously described plant growth promoting and/or biocontrol agents. In tomato, biochar treatments positively enhanced plant height and leaf size, but had no effect on flower and fruit yield. The positive impacts of biochar on plant response were not due to direct or indirect effects on plant nutrition, as there were no differences between control and treatments in leaf nutrient content. Nor did biochar affect the field capacity of the soilless mixture. A number of organic compounds belonging to various chemical classes, including n-alkanoic acids, hydroxy and acetoxy acids, benzoic acids, diols, triols, and phenols were identified in organic solvent extracts of the biochar. We conjecture two related alternatives to explain the improved plant performance under biochar treatment: (i) the biochar stimulated shifts in microbial populations towards beneficial plant growth promoting rhizobacteria or fungi, due to either chemical or physical attributes of the biochar; or (ii) low doses of biochar chemicals, many of which are phytotoxic or biocidal at high concentrations, stimulated plant growth at low doses (hormesis).
695 citations
TL;DR: The structure and bacterial diversity of the rhizosphere is reviewed and mechanisms of plant growth promotion by the PGPR are discussed, which show a variety of interactions between themselves as well as with the plant.
Abstract: Sustainable agricultural practices are the answer to multifaceted problems that have resulted due to prolonged and indiscriminate use of chemical based agronomic tools to improve crop productions for the last many decades. The hunt for suitable ecofriendly options to replace the chemical fertilizers and pesticides has thus been aggravated. Owing to their versatile and unmatchable capacities microbial agents offer an attractive and feasible option to develop the biological tools to replace/supplement the chemicals. Exploring the microorganisms that reside in close proximity to the plant is thus a justified move in the direction to achieve this target. One of the most lucrative options is to look into the rhizosphere. Rhizosphere may be defined as the narrow zone of soil that surrounds and get influenced by the roots of the plants. It is rich in nutrients compared to the bulk soil and hence exhibit intense biological and chemical activities. A wide range of macro and microorganisms including bacteria, fungi, virus, protozoa, algae, nematodes and microarthropods co-exist in rhizosphere and show a variety of interactions between themselves as well as with the plant. Plant friendly bacteria residing in rhizosphere which exert beneficial affect on it are called as plant growth promoting rhizobacteria (PGPR). Here we review the structure and bacterial diversity of the rhizosphere. The major points discussed here are: (1) structure and composition of the rhizosphere (2) range of bacteria found in rhizosphere and their interactions with the plant with a particular emphasis on PGPR (3) mechanisms of plant growth promotion by the PGPR (4) rhizosphere competence.
228 citations
Cites background from "Screening siderophore producing bac..."
...Also contribute towards phytopathogen inhibition Pseudomonas, Bacillus, Serratia, Rhodococcus, Acinetobacter Chaiharn et al. (2009), Koo and Cho (2009), Rokhbakhsh-Zamin et al. (2011), Sahu and Sindhu (2011) Phosphate solubilization Conversion of insoluble forms of phosphorus to plant accessible…...
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...Also contribute towards phytopathogen inhibition Pseudomonas, Bacillus, Serratia, Rhodococcus, Acinetobacter Chaiharn et al. (2009), Koo and Cho (2009), Rokhbakhsh-Zamin et al. (2011), Sahu and Sindhu (2011) Phosphate solubilization Conversion of insoluble forms of phosphorus to plant accessible form, making it available to the plants....
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TL;DR: In conclusion, Streptomyces bacteria appear to be promising biocontrol agents against a wide range of phytopathogenic fungi, which is not surprising given their ability to produce various bioactive compounds, but further studies on the isolation, formulation and application methods of StrePTomyces along with field experiments are required to establish them as effective biocOntrol agents.
Abstract: Rice is a staple food source for more than three billion people worldwide. However, rice is vulnerable to diseases, the most destructive among them being rice blast, which is caused by the fungus Magnaporthe oryzae (anamorph Pyricularia oryzae). This fungus attacks rice plants at all stages of development, causing annual losses of approximately 10%-30% in various rice producing regions. Synthetic fungicides are often able to effectively control plant diseases, but some fungicides result in serious environmental and health problems. Therefore, there is growing interest in discovering and developing new, improved fungicides based on natural products as well as introducing alternative measures such as biocontrol agents to manage plant diseases. Streptomyces bacteria appear to be promising biocontrol agents against a wide range of phytopathogenic fungi, which is not surprising given their ability to produce various bioactive compounds. This review provides insight into the biocontrol potential of Streptomyces against the rice blast fungus, Magnaporthe oryzae. The ability of various Streptomyces spp. to act as biocontrol agents of rice blast disease has been studied by researchers under both laboratory and greenhouse/growth chamber conditions. Laboratory studies have shown that Streptomyces exhibit inhibitory activity against M. oryzae. In greenhouse studies, infected rice seedlings treated with Streptomyces resulted in up to 88.3% disease reduction of rice blast. Studies clearly show that Streptomyces spp. have the potential to be used as highly effective biocontrol agents against rice blast disease; however, the efficacy of any biocontrol agent may be affected by several factors including environmental conditions and methods of application. In order to fully exploit their potential, further studies on the isolation, formulation and application methods of Streptomyces along with field experiments are required to establish them as effective biocontrol agents.
186 citations
Cites background from "Screening siderophore producing bac..."
...Infection with phytopathogenic fungi are among the most worrying of these diseases as it may result in significant crop yield losses, and additionally, some of the fungi produce compounds which are potentially toxic upon consumption (Chaiharn et al., 2009; Suprapta, 2012)....
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TL;DR: Screening for antagonism against this fungal pathogen, one of the more straightforward methods used for the selection of bacterial biocontrol agents, was proven to be a valid strategy for this experimental system.
Abstract: Over the years, many bacterial isolates have been evaluated as potential biocontrol agents against soilborne fungal phytopathogens. However, few of them were ultimately successful after evaluation in field trials. One of the major reasons for this failure is the lack of appropriate screening procedures to select the most suitable microorganisms for disease control in diverse soil environments. For this reason, the study of bacterial screening has a future that is characterised by many technical and conceptual challenges. In this review, we summarise and discuss the convenience of use of the main screening methods currently applied to select bacterial candidates for biocontrol of fungal and oomycete soilborne phytopathogens. Also, a comparative case study of the application of different screening methods applied to an experimental pathosystem is shown, revealing the success of bacterial candidates selected by different strategies for biocontrol of the phytopathogenic fungus Rosellinia necatrix in avocado plants. Screening for antagonism against this fungal pathogen, one of the more straightforward methods used for the selection of bacterial biocontrol agents, was proven to be a valid strategy for this experimental system.
147 citations
Cites background from "Screening siderophore producing bac..."
...…media should be used (Schwyn and Neilands 1987), which has resulted in selection of bacterial BCAs belonging to the genera Pseudomonas, Bacillus and Kocuria against many fungal soilborne phytopathogens such as Fusarium oxysporum, Pyricularia oryzae, and Sclerotium spp. (Chaiharn et al. 2009)....
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TL;DR: It is demonstrated that under iron limiting conditions different strains of A. brasilense produce siderophores, exhibiting different yields and rates of production according to their origin, suggesting that some strains of C. acutatum could act as biocontrol agent preventing anthracnose disease in strawberry.
Abstract: Anthracnose, caused by the fungus Colletotrichum acutatum is one of the most important diseases in strawberry crop. Due to environmental pollution and resistance produced by chemical fungicides, nowadays biological control is considered a good alternative for crop protection. Among biocontrol agents, there are plant growth-promoting bacteria, such as members of the genus Azospirillum. In this work, we demonstrate that under iron limiting conditions different strains of A. brasilense produce siderophores, exhibiting different yields and rates of production according to their origin. Chemical assays revealed that strains REC2 and REC3 secrete catechol type siderophores, including salicylic acid, detected by thin layer chromatography coupled with fluorescence spectroscopy and gas chromatography-mass spectrometry analysis. Siderophores produced by them showed in vitro antifungal activity against C. acutatum M11. Furthermore, this latter coincided with results obtained from phytopathological tests performed in planta, where a reduction of anthracnose symptoms on strawberry plants previously inoculated with A. brasilense was observed. These outcomes suggest that some strains of A. brasilense could act as biocontrol agent preventing anthracnose disease in strawberry.
136 citations
Cites background from "Screening siderophore producing bac..."
...They can improve vegetal growth by increasing plant nutrient availability through iron uptake and preventing the growth of soil borne pathogens due to iron limitation (Chaiharn et al. 2009; Miethke and Marahiel 2007; O’Sullivan and O’Gara 1992; Sayyed and Chincholkar 2009)....
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