Antagonistic Bacterial Isolates Research Articles

Effectiveness of Antagonistic Bacterial Isolates for Control Rhizoctonia Solani Kuhn on flax and Cotton

Effectiveness of Antagonistic Bacterial Isolates for Control Rhizoctonia Solani Kuhn on flax and Cotton

Biocontrol potential of epiphytic bacteria against Xanthomonas citri pathotypes A and A*

BackgroundCitrus canker caused by the bacterium Xanthomonas citri (Hasse 1915) is known as a dangerous disease that has serious economic impacts on citrus production in many tropical and subtropical countries. In Iran, Citrus canker disease has caused significant damage to various citrus fruits, particularly limes. Nowadays, employing antagonistic bacteria as an effective and environmentally friendly method for plant disease management has gained special importance.ResultsCitrus leaf samples were collected from different regions of Iran, and after isolating epiphytic bacteria, ex planta and in planta investigations concerning antagonistic activities of the isolates against Xanthomonas citri pathotypes A and A* were performed. A total of 94 epiphytic bacterial isolates were isolated from citrus aerial parts. Based on biochemical, physiological, morphological, and genotypic tests, it was determined that these bacteria belong to the Bacillus and Staphylococcus genera. The highest inhibition activity against the pathogenic bacterium was related to isolates D4 and D5. Using the molecular method and the resulting dendrogram, it was found that these isolates were most similar to Bacillus amyloliquefaciens. The present findings demonstrated that pathogenicity test on key lime leaves infected with X. citri pathotypes A and A*, along with the application of the biocontrol strain B. amyloliquefaciens, resulted in a significant reduction in the number of canker lesions.ConclusionThe results strongly suggested that the identified antagonistic bacterial isolates hold promising potential as biocontrol agents for managing citrus bacterial canker disease.

Evaluation of phyllosphere bacterial biocontrol agents for the suppression of rice foliar diseases

AbstractPhyllosphere colonizing antagonistic bacterial isolates were evaluated for managing major rice foliar diseases, namely brown spot caused by Bipolaris oryzae and sheath rot caused by Sarocladium oryzae. Among these various isolates, Pseudomonas aeruginosa isolate 1 effectively inhibited the mycelial growth of B. oryzae and S. oryzae. The volatile compounds of Bacillus subtilis isolates effectively inhibited the mycelial growth of S. oryzae and B. oryzae. Non‐volatile compounds of P. aeruginosa isolate 2 and B. subtilis isolate 1 recorded the maximum inhibition of mycelial growth of B. oryzae and S. oryzae, respectively. P. aeruginosa isolates produced fluorescent pigments and hydrogen cyanide (HCN), whereas isolates of Bacillus spp. did not. All the isolates of P. aeruginosa and Bacillus spp. produced protease enzymes. P. aeruginosa isolates solubilized phosphate, whereas isolates of Bacillus spp. did not. Rice seeds treated with these bacterial suspensions showed improvement in plant growth parameters. The foliar application of two bacterial strains, namely P. aeruginosa isolate 1 + B. subtilis isolate 1 recorded the minimum brown spot and sheath rot disease incidence. Thus, the present showed that phyllosphere colonizing P. aeruginosa and B. subtilis have the potential application for managing foliar fungal diseases of rice plants.

Exploring bioactive compounds from a symbiotic bacterial strain of Spongiobacter sp.

Marine sponges are a host of different symbiotic groups of bacteria playing crucial roles in the protection and survival of marine sponges. Marine symbiotic bacteria from sponges are promising sources of bioactive chemicals and are increasingly being investigated. Therefore, the present study was undertaken to analyze total compounds from active symbiotic bacterial strain from sponge, Pione vastifical. Potential bacterial strain EA276 previously isolated from P. vastifical and was identified as Spongiobacter sp. Among 57 isolates, only 42% exhibited antagonistic activity. Four major classes of bacteria were reported previously where γ-Proteobacteria, was the dominant class. From these active antagonistic bacterial isolates, a potential bacterial strain Spongiobacter sp. EA276 was selected, and total metabolites were identified using GC and LC-MS analyses. Using LC-MS analysis bioactive compounds Dichlorphenamide, Amifloxacin and Carbenicillin are identified in both positive and negative mode. Plant growth hormones, Indole-3-acetic acid and Methyl jasmonate were identified using GC-MS analysis from culture extract of strain Spongiobacter sp. EA276. Our results highlighted the significance of marine flora inhabiting sponges from the Red Sea as potential source of bioactive compounds and plant growth hormones of biological and agricultural significance.

Toprak örneklerinden bakteri izolatlarının izolasyonu ve nohut solgunluğu hastalığına neden olan Fusarium oxysporum f. sp. ciceris’e karşı in vitro antagonistik potansiyellerinin belirlenmesi

In 2021, post-harvest soil samples were taken from fields where chickpea and wheat were grown in Yozgat province to isolate bacteria. Of 74 isolates obtained from soil samples, 14 nonpathogenic isolates were evaluated for their inhibitory potential against two pathogenic isolates (YBUFoc9 and YBUFoc2) of Fusarium wilt disease agent Fusarium oxysporum f. sp. ciceris. Antagonistic bacterial isolates were identified as Bacillus spp. by Blastn analysis based on their 16S rDNA nucleotide sequences. Among them, 2 isolates were identified as B. amyloliquefaciens (BM23 and BM40), 3 isolates as B. subtilis (BM8, BM32, and BM105), 6 isolates as B. cereus (BM10, BM69, BM70, BM104, BM111 and BM215), 2 isolates as B. megaterium (BM44 and BM135) and 1 isolate as B. pumilus (BM28). No effective isolate of any genus other than Bacillus spp. was found. They inhibited mycelial growth of isolates YBUFoc9 and YBUFoc2 from 0 to 78.50% and from 0 to 58.33%, respectively. Among the 5 different species, B. amyloliquefaciens (BM23 and BM40) and B. subtilis (BM8, BM32, and BM105) showed the strongest inhibitory activity against the two fungal isolates under in vitro conditions. In further studies, the biocontrol properties of the most effective isolates (BM23, BM40, BM8, BM32 and BM105) will be investigated and compared with approved fungicides for their fungicidal activity.

Bacteriobiota of the Cave Church of Sts. Peter and Paul in Serbia—Culturable and Non-Culturable Communities’ Assessment in the Bioconservation Potential of a Peculiar Fresco Painting

The principal aim of this study was to determine bacterial diversity within the Cave Church of Sts. Peter and Paul, via culturable and non-culturable approaches, and elucidate the antifungal potential of autochthonous antagonistic bacterial isolates against biodeteriogenic fungi. Furthermore, whole-genome sequencing of selected bacterial antagonists and the analysis of genes included in the synthesis of secondary metabolites were performed. With the highest RA values, determined in metabarcoding analysis, phyla Actinobacteriota (12.08-54.00%) and Proteobacteria (25.34-44.97%) dominated most of the samples. A total of 44 different species, out of 96 obtained isolates, were determined as part of the culturable bacteriobiota, with the predominance of species from the genus Bacillus. Bacillus simplex was the only isolated species simultaneously present in all investigated substrata within the church. The best antagonistic activity against 10 biodeteriogenic fungi was documented for Streptomyces anulatus, followed by Bacillus altitudinis, Chryseobacterium viscerum, and Streptomyces sp. with their highest PGI% values ranging of from 55.9% to 80.9%. These promising results indicate that characterized bacteria are excellent candidates for developing biocontrol strategies for suppressing deteriogenic fungi responsible for the deterioration of investigated fresco painting. Finally, isolate 11-11MM, characterized as Streptomyces sp., represents a new species for science prompting the need for further study.

Screening and characterization of antibiotic producing bacteria from rhizospheric soil against fungal phytopathogens

In this study, antagonistic bacteria were isolated from rhizospheric soil collected from Himachal Pradesh (i.e., Solan and Hamirpur) and Punjab (i.e., Jalandhar and Pathankot). Sixty- eight bacteria were isolated and screened for antifungal activity against Botrytis oryzae, Aspergillus flavus, and Fusarium oxysporum. Three isolates, i.e., S7, S57, and S51, showed maximum inhibition for antifungal activity by using the agar streak method and were further selected for in vitro characterization. In vitro antifungal antibiotic study by using agar diffusion assay of isolates, i.e., S7, S57, and S51 at O.D. 2.0 showed maximum inhibition of 99% against Botyritis oryzae, Fusarium oxysporum, and Aspergillus flavus after seven days of incubation. Antibiotic assays using cell-free supernatant of antagonistic bacterial isolates, i.e., S7 and S57, showed complete inhibition at 10% against Botyritis oryzae and Fusarium oxysporum, whereas isolate S51 showed complete inhibition at 20% against Aspergillus flavus. The bacterial isolates were partially identified based on morphological and biochemical characteristics. The selected antagonistic bacterial isolates S7 and S57 appeared to be similar to Bacillus sp. and S51 to Actinomycete sp. Thus, the present study concludes that these bacterial isolates could serve as proficient biocontrol inoculants in the integrated management of soil-borne diseases in different crops under natural environmental conditions.

Potential for Biological Control of Pythium schmitthenneri Root Rot Disease of Olive Trees (Olea europaea L.) by Antagonistic Bacteria.

Several diseases affect the productivity of olive trees, including root rot disease caused by Pythium genera. Chemical fungicides, which are often used to manage this disease, have harmful side effects on humans as well as environmental components. Biological management is a promising control approach that has shown its great potential as an efficient eco-friendly alternative to treating root rot diseases. In the present study, the antagonistic activity of ten bacterial isolates was tested both in vitro and in planta against Pythium schmitthenneri, the causal agent of olive root rot disease. These bacterial isolates belonging to the genera Alcaligenes, Pantoea, Bacillus, Sphingobacterium, and Stenotrophomonas were chosen for their potential antimicrobial effects against many pathogens. Results of the in vitro confrontation bioassay revealed a high reduction of mycelial growth exceeding 80%. The antifungal effect of the volatile organic compounds (VOCs) was observed for all the isolates, with mycelial inhibition rates ranging from 28.37 to 70.32%. Likewise, the bacterial cell-free filtrates showed important inhibition of the mycelial growth of the pathogen. Overall, their efficacy was substantially affected by the nature of the bacterial strains and their modes of action. A greenhouse test was then carried out to validate the in vitro results. Interestingly, two bacterial isolates, Alcaligenes faecalis ACBC1 and Bacillus amyloliquefaciens SF14, were the most successful in managing the disease. Our findings suggested that these two antagonistic bacterial isolates have promising potential as biocontrol agents of olive root rot disease.

Selection and Characterization of Antagonistic Microorganisms for Biological Control of Acidovorax citrulli Causing Fruit Rot in Watermelon

This study was performed to screen the efficacy of antagonistic bacterial isolates from various sources against the bacterial fruit blotch (BFB) causing pathogen (Acidovorax citrulli) in cucurbit crops. In addition, plant growth promoting traits of these antagonistic bacterial isolates were characterized. Two thousand seven hundred ninety-four microorganisms were isolated from the collected samples. Molecular identification revealed two A. citrulli out of 2,794 isolates. In vitro antagonistic results showed that, among the 28 antagonistic bacterial isolates, 24 and 14 bacterial isolates exhibited antagonism against HPP-3-3B and HPP-9-4B, respectively. Antagonistic and growth promotion characterization of the antagonistic bacterial isolates were further studied. Results suggested that, 4 antagonistic bacteria commonly showed both antagonism and growth promotion phenotypes. Moreover, 3 isolates possessed growth promoting activities. Overall results from this study suggests that BFB causing bacterial pathogen (A. citrulli) was suppressed in in vitro antagonism assay by antagonistic bacterial isolates. Furthermore, these antagonistic bacterial isolates possessed growth promotion and antagonistic enzyme production ability. Therefore, data from this study can provide useful basic data for the in vivo experiments which ultimately helps to develop the eco-friendly agricultural materials to control fruit rot disease in cucurbit crops in near future.

Biocontrol effects of endophytic and rhizospheric bacteria against the root pathogen Fusarium oxysporum of hot pepper (Capsicum annum L.)

Plant disease needs to be controlled to keep the quality ofproducts and the abundance of food produced by farmersall over the world. Hot pepper production in Ethiopia hasbeen reduced from time to time. This is mainly due to theoutbreak of different diseases especially fusarium wilt inthe hot pepper growing areas. The objective of this studywas to isolate and characterize Plant Growth PromotingBacteria from the hot pepper rhizosphere and internal tissueswith potential biocontrol activity against Fusariumoxysporum. Thirty healthy and vigorous hot pepper plantswith intact roots and soil from the rhizospheric region werecollected randomly from hot pepper growing areas of YimaliKebele. A total of 23 endophytic and rhizospheric bacteriawere isolated from the hot pepper root and rhizosphericsoil. The combined endophytic and rhizospheric bacteriashowed a significant effect on the growth of F. oxysporumthan single isolates (P d”0.05). The bacteria isolated fromMarkofana hot pepper varieties of black clay soil showed abetter antagonistic effect on F. oxysporum than bacteriaisolated from local hot pepper varieties of reddish sandysoil. A significant percentage of inhibition between combinedendophytic and rhizospheric bacteria [endophytic (GE) +rhizospheric (GR) isolates] compared to GE+GE and GR+GR(P =0.002) was obtained. Antagonistic bacterial isolates wereable to produce different hydrolytic enzymes such aschitinase, protease, and cellulase. Bacillus species showedbetter antagonistic performance and decreased radial growthof F. oxysporum than Pseudomonas species.

Biocontrol properties from phyllospheric bacteria isolated from Solanum lycopersicum and Lactuca sativa and genome mining of antimicrobial gene clusters

BackgroundBiocontrol agents are sustainable eco-friendly alternatives for chemical pesticides that cause adverse effects in the environment and toxicity in animals including humans. An improved understanding of the phyllosphere microbiology is of vital importance for biocontrol development. Most studies have been directed towards beneficial plant-microbe interactions and ignore the pathogens that might affect humans when consuming vegetables. In this study we extended this perspective and investigated potential biocontrol strains isolated from tomato and lettuce phyllosphere that can promote plant growth and potentially antagonize human pathogens as well as plant pathogens. Subsequently, we mined into their genomes for discovery of antimicrobial biosynthetic gene clusters (BGCs), that will be further characterized.ResultsThe antimicrobial activity of 69 newly isolated strains from a healthy tomato and lettuce phyllosphere against several plant and human pathogens was screened. Three strains with the highest antimicrobial activity were selected and characterized (Bacillus subtilis STRP31, Bacillus velezensis SPL51, and Paenibacillus sp. PL91). All three strains showed a plant growth promotion effect on tomato and lettuce. In addition, genome mining of the selected isolates showed the presence of a large variety of biosynthetic gene clusters. A total of 35 BGCs were identified, of which several are already known, but also some putative novel ones were identified. Further analysis revealed that among the novel BGCs, one previously unidentified NRPS and two bacteriocins are encoded, the gene clusters of which were analyzed in more depth.ConclusionsThree recently isolated strains of the Bacillus genus were identified that have high antagonistic activity against lettuce and tomato plant pathogens. Known and unknown antimicrobial BGCs were identified in these antagonistic bacterial isolates, indicating their potential to be used as biocontrol agents. Our study serves as a strong incentive for subsequent purification and characterization of novel antimicrobial compounds that are important for biocontrol.

Biological control of fungal pathogens of tomato (Lycopersicon esculentum) by chitinolytic bacterial strains

The need to increase food production and to reduce the pollution caused by synthetic chemicals has led to a search for biocontrol agents against plant pathogens. In the present study, a total of 37 chitinolytic bacteria were isolated from the rhizospheric soil of tomatoes using a chitin agar medium. In vitro bacterial isolates, that is, TD9, TD11, TD15, and TD24 showed strong antagonistic and enzymatic activities against Rhizoctonia (8%-55%), Fusarium (31%-48%), Colletotrichum (24%-49%), and Aspergillus on a dual culture plate and enzyme assay. Furthermore, these putative antagonistic bacterial isolates were identified as Pantoea agglomerans (TD9), Bacillus subtilis (TD11), Bacillus cereus (TD15 and TD24) using 16S rRNA sequence analysis. Additionally, in culture filtrate in vivo assay, the isolates TD11 and TD15 inhibited the growth of Rhizoctonia solani about 40% and Fusarium oxysporum about 80%. However,in the pot trials, these two bacterial isolates (TD11 and TD15) considerably suppressed the disease rate in tomatoes caused by Fusarium and Rhizoctonia fungal species. Moreover, it was concluded that B. subtilis (TD11) was found to be the most promising putative biocontrol agent, inhibiting the fungal diseases of tomatoes by 50% and showing versatile antagonistic potential.

Diversity of culturable bacteria endowed with antifungal metabolites biosynthetic characteristics associated with tea rhizosphere soil of Assam, India

BackgroundRhizosphere soil is a crucial niche for the diverse beneficial microbial communities in plant-microbe interactions. This study explores the antagonistic potential and diversity of the rhizosphere soil bacteria from commercial tea estates of Assam, India which comes under the Indo-Burma mega-biodiversity hotspot. Rhizosphere soil samples were collected from six different tea estates to isolate the bacteria. The bacterial isolates were subjected to evaluate for the antagonistic activity against fungal pathogens. The potential isolates were investigated for chitinase production and the presence of chitinase gene. The bacterial genetic diversity was studied by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and BOX-PCR fingerprinting.ResultsA total of 217 rhizobacteria were isolated from tea rhizosphere soil, out of which 50 isolates exhibited the potential antagonistic activity against fungal pathogens. Among them, 12 isolates showed extracellular chitinase activity and the presence of chitinase genes. The chitinase genes were sequenced and the analysis of the sequences was performed by using PDB protein databank at the amino acid level. It showed the presence of ChiA and ChiA74 gene in the 6 most potent isolates which are involved in the hydrolysis of chitin. These isolates also exhibited antagonistic activity against all tested fungal pathogens. The diversity of 50 antagonistic bacterial isolates were analyzed through ARDRA and BOX-PCR fingerprinting. Diversity analysis and molecular identification of the rhizosphere isolates revealed that these antagonistic isolates predominantly belonged to the genus Bacillus followed by Enterobacter, Serratia, Lysinibacillus, Pseudomonas, and Burkholderia.ConclusionThe present study establishes that rhizobacteria isolated from the poorly explored tea rhizosphere soil could be a rich reservoir for the investigation of potential antagonistic bacterial candidates for sustainable agricultural and industrial applications.

Bacterial antagonists against Ganoderma lucidum the incitant of root rot of Indian Mesquite

Indian arid regions recently witnessed large scale mortality in the Indian mesquite {Prosopis cineraria Druce}, locally known as Khejri tree, due to root rot caused by Ganoderma lucidum. Use of biological control agents offers an attractive alternative to manage Ganoderma induced diseases in Khejri tree, without any negative impact on the environment. Therefore, efforts were made to isolate antagonistic bacterial isolates from infected trees of P. cineraria. Several soil samples were analysed and two bacterial isolates: strains AZAC-1and AZ-11were selected as potential antagonists against G.lucidum from arid soils. Taxonomic identity of the two strains was ascertained using 16S rRNA in EzBioCloud. The strains showed over 99.7% similarity and were identified as Streptomyces sp.strain AZAC-1 (MK459414) and Bacillus sp.strain AZ-11(MH304296).

Siderophore containing extract from Serratia plymuthica AED38 as an efficient strategy against avocado root rot caused by Phytophthora cinnamomi

ABSTRACT Phytophthora cinnamomi Rands. is a widely distributed pathogen in avocado crops. Root rot caused by Phytophthora cinnamomi decreases the yield and growers are to establish new productive areas in order to meet demand which in turn is causing the loss of native forests. Therefore, sustainable production of avocado is only possible by addressing yield issues and the efficient use of lands. In this work, the effectiveness of two promising antagonistic bacterial isolates associated to healthy avocado trees to protect avocado seedlings against P. cinnamomi was assessed. First, the virulence of five isolates of P. cinnamomi from different avocado growing regions in Colombia was evaluated. The most virulent isolate was used to infect five-month-old avocado seedlings. The native bacterial isolates, both identified as Serratia plymuthica, were used to produce extracts in solid medium and their inhibitory activity against P. cinnamomi was tested. One of the extracts was selected and submitted to a bioguided metabolite isolation. A siderophore molecule (serratiochelin C) was purified and fully characterised by Nuclear Magnetic Resonance. Finally, the protective capacity of one bacterial extract was assessed in vivo against the infection of Phytophthora cinnamomi on avocado along with a commercial product based on fosetyl-aluminum. The crude metabolic extract of S. plymuthica AED38 was found to be effective and nontoxic on seedlings at 60 µg.mL−1. The results were comparable with the effect of fosetyl-aluminum at 0.5 µg.mL−1. S. plymuthica extracts possess a promising potential as bioproduct for the control of P. cinnamomi.

Paenibacillus polymyxa and Bacillus aryabhattai as Biocontrol Agents against Ralstonia solanacearum In Vitro and In Planta

The present study aimed to biologically controlling the potato bacterial wilt disease which caused by Ralstonia solanacearum by antagonistic bacterial isolates which isolated from soil. Two bacterial isolates (coded, MAS400 and MAS100) obtained from soil of some field grown potato crops was tested to against Ralstonia solanacearum bacterium in vitro and in planta. The isolates showed various ability to inhibit R. solanacerum growth in vitro. The isolate MAS400 exhibited highly inhibitory activity (3.7 cm), while the isolate MAS100 showed moderate antagonistic activity (0.9 cm). Molecular identification and 16S rDNA sequencing for the antagonistic bacterial isolates showed that, the isolate MAS400 is Bacillusaryabhattai withpercent identity 80.56% and the isolate MAS100 is Paenibacillus polymyxa withpercent identity 97.63% compared to known bacterial sequences in the NCBI (National Center for Biotechnology Information) databases. The isolate MAS100 was deposited in Genebank NCBI with accession number MN971671. Assessment of antagonistic bacteria as biocontrol agents for suppressionpotato bacterial wilt disease showed that, symptoms were less severe and the appearance of wilt symptom on infected plants was delayed compared to the control. Trials with Paenibacillus polymyxa isolate on potato plants had a lower disease incidence (20 %) with maximum disease reduction (80 %), whereas Bacillusaryabhattai isolate had a higher disease incidence on potato plants (60 %), with lower disease reduction (40 %). Isolates Paenibacillus polymyxa showed the highest suppression on potato plants.

The effective antagonistic potential of plant growth-promoting rhizobacteria against Alternaria solani-causing early blight disease in tomato plant

Tomato plants can be infected by several diseases, among them, the early blight disease, caused by the necrotrophic fungus Alternaria solani is very dangerous. Plant growth promoting rhizobacteria (PGPR) are enhanced the plant growth and suppress plant diseases. The current study was conducted in a pot experiment to investigate the bio-efficacy antagonistic bacterial isolates as either individual or combination against tomato early blight disease. Disease severity and protection percent, morphological indicators as well as yield characters were recorded. In vitro antagonistic activity assay of PGPR against A. solani was estimated. Metabolic indicators of resistance in plant as response to induction of systemic resistance (ISR) were recorded. Our results indicated that, PGPR isolates were reduced the percent disease severity by 13.0 % and recorded highly protection percent by 84.3 %. The beneficial effects of the used elicitors were extended to increase not only the morphological characters (shoot lengths, root lengths and leaflet number/plant) but also the yield characters. All tested elicitors caused the marked significant increases in the photosynthetic pigments. PGPR isolates were exhibited the most potent effect in terms of the contents of chlorophyll a, b and the total chlorophyll (a + b) followed by plants treated with A. xylosoxidans (A3), B. subtilis (B1) and L. fusiformis (L2) in the infected plants, compared to the non-treated infected control. PGPR isolates were increased total phenol (56.15 mg/100 g dry wt.), free proline (1.435 mg/g dry wt.), total protein (1.198 mg/g dry wt.) and the activities of peroxidase (0.705 μg/100 g fresh wt.) and polyphenol oxidase (1.281 μg/100 g fresh wt.). All the tested treatments resulted in increasing the contents of indole acetic acid (IAA), Abscisic Acid (ABA), Salicylic Acid (SA), and Jasmonic acid (JA) compared with those of the infected plants. PGPR isolates’ antifungal activity may be attributed to cell wall disruption of A. solani and the normal conidial development inhibition. Therefore, due to these outstanding properties of PGPR isolates as plant growth promoters and antifungal activity, this study could give insights for solving serious agricultural challenges and particularly in the treatment of A. solani invasion across the tomato plants.

A Possibility of using Antagonistic Bacterial Isolates in Controlling Fusarium Wilt of Chrysanth (Chrysanthemum sp.)

A Possibility of using Antagonistic Bacterial Isolates in Controlling Fusarium Wilt of Chrysanth (Chrysanthemum sp.)

Biocontrol potential of five Burkholderia and Pseudomonas strains against Colletotrichum truncatum infecting chilli pepper

ABSTRACTThe effect of bacterial antagonism against the causal agent, Colletotrichum truncatum was assessed as a potential alternative in managing anthracnose in chilli pepper. Out of 104 contrasting bacterial colonies isolated from rhizosphere soil of a forest floor, five isolates caused the radial growth inhibition greater than 90% (Significant at p < 0.05 level) of C. truncatum in dual cultures. Based on 16S rRNA analysis, these antagonistic bacterial isolates were identified as Pseudomonas aeruginosa, Burkholderia arboris, Burkholderia gladioli and Burkholderia rinojensis. The selected promising antagonists showed nearly 100% inhibition of the spore germination of C. truncatum in vitro. These antagonists produced antifungal compounds which are diffusible in nature. Microscopic studies of blackened fungal hyphae, which were subjected to antagonism showed many deformations such as thickening, swelling and malformation. In vivo study revealed that C. truncatum inoculated chilli pepper seeds treated with the five antagonists significantly inhibited the incidence of seed colonisation (p < 0.05) by the pathogen. At the post emergence stage, the survival percentages and vigour indices of all the antagonists’ treatments, except B. rinojensis strain 1, were significantly higher compared to the untreated control. The efficacy of the selected antagonists in managing anthracnose fruit rot was 100% at the colour breaking stage of chilli pepper fruits. These bacterial antagonists had a negative effect on C. truncatum spore attachment and subsequent colonisation on chilli pepper leaves except in the treatment of B. arboris. The results of in-vitro and in-vivo studies, suggest that the screened antagonistic bacterial isolates are potential biocontrol agents and need to be further studied for the biochemical basis of their activity against C. truncatum.

Identification of plant growth promoting antagonistic bacteria against Xanthomonas oryzae pv. oryzae in Bangladesh

Background: Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is a major disease and a threat to rice production worldwide. Several biological, chemical and genetic control approaches has resulted the improved management of BLB of rice. Recently, biological control using plant growth-promoting bacteria is emerging as potential alternative to chemicals. Therefore, identification and evaluation of new PGP bacteria from native sources is an essential step to determine their plant growth promoting activities. Objectives The aim of this work was to isolate and identify the plant growth promoting bacteria from rice phylloplane and rhizosphere that antagonistic to X. oryzae pv.oryzae, the causal agent of BLB of rice for eco-friendly management of the disease. Methodology Rice phylloplane and rhizosphere bacteria were isolated from the surface of rice leaves and stem as well as from the soil attached to the roots of rice plants, respectively, by dilution plate technique. The antagonistic activity of these isolated bacteria was determined by dual culture method. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA.Plant growth promoting activities were determined by the production of indole acetic Acid (IAA), siderophore and phosphate solubilization assay. Plant growth promotion was assessed by the determination of root length, shoot length and vigor index. Key findings Sixteen bacterial isolates were identified as antagonist to X. oryzae pv. oryzae out of 300 bacterial isolates by dual culture method. The results revealed that the maximum growth inhibition of X. oryzae pv.oryzae was recorded in plate inoculated with BDISOB05P while the minimum growth inhibition was recorded by BDISOB98P and BDISOB272R. The moderate growth inhibition was recorded in BDISOB241P, BDISOB16P, BDISOB306R, BDISOB242P, BDISOB220R, BDISOB04P, BDISOB258R, BDISOB219R, BDISOB221R, BDISOB275R, BDISOB283R and BDISOB61R. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA. The bacterial isolates were identified BDISOB04P as Pseudomonas putida, BDISOB05P as Pseudomonas putida, BDISOB16P as Bacillus sp., BDISOB98P as Stenotrophomonas maltophilia, BDISOB241P as Burkholderia sp., BDISOB242P as Burkholderia gladioli, BDISOB219R as Pseudomonas taiwanensis, BDISOB220R as Serratia sp., BDISOB221R as Pseudomonas sp., BDISOB222R as Pseudomonas plecoglossicida, BDISOB258R as Pseudomonas putida, BDISOB272R as Stenotrophomonas maltophilia, BDISOB275R as Pseudomonas putida , BDISOB283R as Pseudomonas fluorescens and BDISOB306R as Pseudomonas putida. The results of growth promoting determinants revealed that eight antagonistic bacterial isolates were observed to produce Indole acetic acid (IAA), sixteen bacterial isolates were able to produce siderophore and nine bacterial isolates were found to show phosphate solubilizing capability. The results of plant growth promotion showed that these bacterial isolates can increase the root growth, shoot growth and vigor index. Conclusion The results conceded some of the PGP bacterial isolates seem potential in both growth inhibition of X. oryzae pv. oryzae and growth promotion of rice plants.