Search

Summary: Five bacterial strains with phosphate-solubilizing ability and other plant growth promoting traits increased the plant biomass (20–40%) by paper towel method. Glasshouse and field experiments were conducted using two efficient strains Serratia marcescens EB 67 and Pseudomonas sp. CDB 35. Increase in plant biomass (dry weight) was 99% with EB 67 and 94% with CDB 35 under glasshouse conditions. Increase in plant biomass at 48 and 96 days after sowing was 66% and 50% with EB 67 and 51% and 18% with CDB 35 under field conditions. Seed treatment with EB 67 and CDB 35 increased the grain yield of field-grown maize by 85% and 64% compared to the uninoculated control. Population of EB 67 and CDB 35 were traced back from the rhizosphere of maize on buffered rock phosphate (RP) medium and both the strains survived up to 96 days after sowing. [Copyright &y& Elsevier]

Abstract: Isolates of Pseudomonas fluorescens producing the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) are effective biocontrol agents against soilborne pathogens. A previous study showed that the superior (“premier”) root colonizer P. fluorescens Q8r1-96 (genotype D) utilized trehalose, benzoate and valerate as sole carbon sources but average colonizers Q2-87 (genotype B) and 1M1-96 (genotype L) did not. We tested the utilization of these three carbon sources by a collection of 55 2,4-DAPG-producing P. fluorescens strains from 17 genotypes and found no correlation between a strain''s ability to utilize these carbon sources and superior rhizosphere competence on wheat and pea. Of the strains tested, 73%, 48% and 69% were able to utilize trehalose, benzoate and valerate as sole carbon sources, respectively. With some exceptions, we found a correlation between the utilization of these compounds and previous groupings of these strains by BOX-PCR; genotype D strains utilized all three compounds. Twenty-three strains grew efficiently on root and seed exudates from wheat and pea, with doubling times between 0.9 and 1.6h generation−1 and lag phases between 5 and 8h, comparable to growth on glucose as a sole carbon source. Only 10 strains, including those with “premier” (Q8r1-96) and “average” (Q2-87) rhizosphere competence, showed slower growth in wheat root exudates, with lag phases between 16 and 22h. Results were the same when soil was added to the culture medium. Growth of four strains in media containing glucose or wheat or pea seed exudates as a sole carbon source was not influenced by whether the bacterial cells used as inoculum were harvested from wheat seeds or broth culture. We conclude that the superior ability of some strains to colonize the roots of certain crops cannot be explained by the utilization of the carbon sources tested in our study. [Copyright &y& Elsevier]

The effect of the host plants and their interaction with Meloidogyne incognita (Kofoid and White) Chitwood on the effectiveness of Pochonia chlamydosporia var. catenulata (Kamyscho ex Barron and Onions) Zare and Gams as a biological control agent of root-knot nematodes was studied in glasshouse conditions. Different plant species from the Cuban Intensive Vegetable Production Systems were used to perform the experience. The growth of the fungus in the rhizosphere differed with the host plant. Among the best host plants of P. chlamydosporia var. catenulata were cabbage, salt-wort and cauliflower, resistant crops to M. incognita. The plants infested by M. incognita showed higher levels of fungus colonization than those healthy, and the kidney bean crop was a good host in the presence of the nematode. The use of these crops into rotation systems, with the application of Pochonia chlamydosporia var. catenulata as biological control agent for the management of M. incognita on Intensive Vegetable Production Systems, was recommended. [ABSTRACT FROM AUTHOR]

Abstract: Biological control of soil-borne pathogens is frequently based on the application of antagonistic microorganisms selected solely for their ability to produce in vitro antifungal factors. The aim of this work was to select bacteria that efficiently colonize the roots of avocado plants and display antagonism towards Rosellinia necatrix, the causal agent of avocado white root rot. A high frequency of antagonistic strains (ten isolates, 24.4%) was obtained using a novel procedure based on the selection of competitive avocado root tip colonizers. Amplification and sequencing of the 16S rRNA gene, in combination with biochemical characterization, showed that eight and two of the selected isolates belonged to the genera Pseudomonas and Stenotrophomonas, respectively. Characterization of antifungal compounds produced by the antagonistic strains showed variable production of exoenzymes and HCN. Only one of these strains, Pseudomonas sp. AVO94, produced a compound that could be related to antifungal antibiotics. All of the ten selected strains showed twitching motility, a cell movement involved in competitive colonization of root tips. Production of N-acyl-homoserine lactones and indole-3-acetic acid was also reported for some of these isolates. Resistance to several bacterial antibiotics was tested, and three strains showing resistance to only one of them were selected for biocontrol assays. The three selected strains persisted in the rhizosphere of avocado plants at levels considered crucial for efficient biocontrol, 105–106 colony forming units/g of root; two of them, Pseudomonas putida AVO102 and Pseudomonas pseudoalcaligenes AVO110, demonstrated significant protection of avocado plants against white root rot. [Copyright &y& Elsevier]

Bacillus subtilis RB14-C, which produces the antibiotic iturin A, was investigated for its effectiveness as a biocontrol agent against Rhizoctonia solani infecting tomato using seed coating and/or direct introduction of the bacteria to the soil. The ability of RB14-C to colonize plant roots and produce iturin A in soil, depending on the method of bacterial application, was also determined. Seed coating and the combined treatment (soil and seed bacterization) did not protect seedlings against damping-off caused by R. solani. By contrast, RB14 introduced only to the soil controlled the disease. The total number of RB14-C bacteria on the roots of plants grown from coated seeds was significantly lower than on the roots of plants grown in soil mixed with the bacteria. In the combined treatment, application of B. subtilis with seeds to soil preinoculated with this bacterium, at first suppressed the population of RB14-C in the soil. Then the colonization was generally uniform. The concentration of iturin A in non-planted soil was highest at the beginning of the experiment (i.e. after application of the bacterial suspension) but then decreased, and was undetectable 3 days after incubation. However, after seed planting the antibiotic was produced again around young roots. Bacteria introduced to the soil as a seed coating also released the antibiotic around the seeds. [ABSTRACT FROM AUTHOR]

Diversity within a worldwide collection of 2,4-diacetylphloroglucinol-producing Pseudomonas fluorescens strains was assessed by sequencing the phlD gene. Phylogenetic analyses based on the phlD sequences of 70 isolates supported the previous classification into 18 BOX-PCR genotypes (A–Q and T). Exploiting polymorphisms within the sequence of phlD, we designed and used allele-specific PCR primers with a PCR-based dilution endpoint assay to quantify the population sizes of A-, B-, D-, K-, L- and P-genotype strains grown individually or in pairs in vitro, in the rhizosphere of wheat and in bulk soil. Except for P. fluorescens Q8r1-96, which strongly inhibited the growth of P. fluorescens Q2-87, inhibition between pairs of strains grown in vitro did not affect the accuracy of the method. The allele-specific primer-based technique is a rapid method for studies of the interactions between genotypes of 2,4-diacetylphloroglucinol producers in natural environments. [ABSTRACT FROM AUTHOR]

Molecules exuded by plant roots are thought to act as signals to influence the ability of microbial strains to colonize the roots and to survive in the rhizosphere. Differential bacterial responses to signals from different plant species may mediate the selection of specific rhizosphere populations. Very little, however, is known about the effects of plant exudates on patterns of bacterial gene expression. Here, we have tested the concept that plant root exudates modulate expression of bacterial genes involved in establishing microbe—plant interactions. We have examined the influence on the Pseudomonas aeruginosa PA01 transcriptome of exudates from two varieties of sugarbeet that select for genetically distinct pseudomonad populations in the rhizosphere. The response to the two exudates showed only a partial overlap; the majority of those genes with altered expression was regulated in response to only one of the two exudates. Genes with altered expression included those with functions previously implicated in microbe-plant interactions, such as aspects of metabolism, chemotaxis and type III secretion, and a subset with putative or unknown function. Use of a panel of mutants with targeted disruptions allowed us to identify previously uncharacterized genes with roles in the competitive ability of P. aeruginosa in the rhizosphere within this subset. No genes with host-specific effects were identified. Homologues of the genes identified occur in the genomes of both beneficial and pathogenic root-associated bacteria, suggesting that this strategy may help to elucidate molecular interactions that are important for biocontrol, plant growth promotion, and plant pathogenesis. [ABSTRACT FROM AUTHOR]

g.k. kishore, s. pande and a.r. podile. 2005.To isolate and characterize groundnut-associated bacterial isolates for growth promotion of groundnut in field.Three hundred and ninety-three groundnut-associated bacteria, representing the geocarposphere, phylloplane and rhizosphere, and endophytes were applied as seed treatment in greenhouse. Maximum increase in plant biomass (up to 26%) was observed following treatment with a rhizosphere isolate identified asBacillus firmisGRS 123, and two phylloplane isolatesBacillus megateriumGPS 55 andPseudomonas aeruginosaGPS 21. There was no correlation between the production ofl-tryptophan-derived auxins and growth promotion by the test isolates. Actively growing cells and peat formulations of GRS 123 and GPS 55, and actively growing cells of GPS 21, significantly increased the plant growth and pod yield (up to 19%) in field. Rifampicin-resistant mutants of GRS 123 and GPS 21 colonized the ecto- and endorhizospheres of groundnut, respectively, up to 100 days after sowing (DAS), whereas GPS 55 was recovered from both the habitats at 100 DAS.Seed bacterization with phylloplane isolates promoted groundnut growth indicating the possibility of isolating rhizosphere beneficial bacteria from different habitats.Identification of phylloplane bacteria as effective plant growth-promoting rhizobacteria (PGPR) broadens the spectrum of PGPR available for field application. [ABSTRACT FROM AUTHOR]

Abstract: Wholesale container-grown ornamentals are often maintained at the nursery for at least two growing seasons and are subject to infestation by black vine weevil (BVW), Otiorhynchus sulcatus F., for several months each year. Therefore, a potting media amendment aimed at controlling BVW needs to persist for an extended period of time. These studies were conducted to determine the persistence and ecology of Metarhizium anisopliae (Metchnikoff) Sorokin incorporated into peat and bark-based potting media with and without a crab meal amendment in container-grown Picea abies ‘Nidiformis.’ Rooted cuttings of P. abies were planted into potting media amended with M. anisopliae (1g of formulated product/L; ∼6 log10 CFU/g dry potting media). The fungal population in bulk potting media was quantitatively determined using selective media at 14, 21, 28, 35, 49, 63, 77, 91, 105, 119, 143, 175, 203, 231, 258, 287 and 342days. The fungal population in the rhizosphere was quantitatively determined at 203, 231, 258, 287, and 342days. M. anisopliae colonized the rhizosphere of P. abies and the fungal population in the rhizosphere was significantly greater than in the surrounding bulk media. M. anisopliae persisted in the peat and bark-based potting media at 6.22 and 5.74log10 CFU/g dry potting media for 342days, respectively. Bioassays using bark and peat-based potting media inoculated with M. anisopliae at 6 log10 CFU/g dry potting media resulted in 93.5% and 97.5% infection of last instar BVW, respectively. P. abies roots inoculated with M. anisopliae infected 76% of 2nd–3rd instar BVW. Inoculation of roots with M. anisopliae represents a novel method for delivering entomopathogenic fungi and would greatly reduce application costs. Factors associated with fungal biology outside the host may be more important than virulence in a laboratory bioassay. [Copyright &y& Elsevier]

s.s. shaukat and i.a. siddiqui. 2003. To assess whether Pseudomonas fluorescens strain CHA0 and its genetically modified derivatives, CHA0/pME3424 (antibiotic over-producer) and CHA89 (antibiotic-deficient) could have an impact on the fungal community structure and composition in the rhizosphere of mungbean. Under glasshouse conditions, mungbean was grown repeatedly in the same soil, which was inoculated with CHA0, CHA0/pME3424, CHA89 or was left untreated. Treatments were applied to soil at the start of each 36-day mungbean growth cycle, and their effects on the diversity of the rhizosphere populations of culturable fungi were assessed at the end of the first, second and third cycles. The effects of CHA0 and CHA0/pME3424 did differ from the controls while CHA89 did not. Whereas all major fungal species were frequently isolated from both bacterized and nonbacterized rhizospheres, certain fungal species were exclusively promoted or specifically suppressed from Pseudomonas-treated soils. In general, fungal diversity and equitability tended to decrease with time while species richness slightly increased. Whilst a total of 29 fungal species were isolated from the mungbean rhizosphere, only eight species colonized the root tissues. Soil inoculation with Ps. fluorescens CHA0 or CHA0/pME3424 altered fungal community structure in mungbean rhizosphere but strain CHA89 failed to produce such effect. Pseudomonas fluorescens-mediated alteration in the composition and structure of fungal communities might have acute or lasting effects on ecosystem functioning. Furthermore, the study provides useful data pertinent to characterization of the fate of genetically modified inoculants (e.g. antibiotic-overproducing Pseudomonas strains) released into the environment. [ABSTRACT FROM AUTHOR]

The mechanisms by which seed-applied bacteria colonize the rhizosphere in the absence of percolating water are poorly understood. Without mass flow, transport of bacteria by growing roots or soil animals, particularly nematodes may be important. We used a sand-based microcosm system to investigate the ability of three species of nematodes (Caenorhabditis elegans, Acrobeloides thornei and a Cruznema sp.) to promote rhizosphere colonization by four strains of beneficial rhizobacteria. In nearly all cases, rhizosphere colonization was substantially increased by the presence of nematodes, irrespective of bacterial or nematode species. Our results suggest that nematodes are important vectors for bacteria rhizosphere colonization in the absence of percolating water. [Copyright &y& Elsevier]

AbstractCalystegines are plant secondary metabolites produced by the roots of a few plant species, and the ability to catabolize calystegines is infrequent in rhizosphere bacteria. In Sinorhizobium meliloti Rm41, the endosymbiont of the legume Medicago sativa, this ability results from the presence of the genes cac (for calystegine catabolism) located on the nonsymbiotic plasmid pRme41a. The effect of the cac catabolic plasmid pRme41a on the ability of Rm41 to colonize the rhizosphere of calystegine-positive plants was studied using derivatives of Rm41 with or without cac catabolic plasmid. When strains were inoculated alone, the presence of a cac catabolic plasmid had no effect on their colonization of the rhizosphere, regardless of whether plants produced calystegines or not. However, a spontaneous rifampicin-resistant mutant of Rm41 containing a cac catabolic plasmid reached population levels in the rhizosphere of calystegine-positive plants that were several orders of magnitude higher than those of the same strain without the plasmid, when each was co-inoculated with a derivative of Rm41 cured of pRme41a. In contrast, the cac catabolic plasmid provided little or no selective advantage in the rhizosphere of calystegine-negative plants. In conclusion, the cac catabolic plasmid pRme41a can contribute to the ability of S. meliloti Rm41 to colonize the rhizosphere of alternative, nonlegume plant hosts producing calystegines. [ABSTRACT FROM AUTHOR]

[Display omitted] • First described the occurrence of ginger bark cracking disease (GBCD) in detail. • First report on the biocontrol potential of B. altitudinis on GBCD. • Checking dynamic change of B. altitudinis by real-time PCR. • Evaluated the impact of B. altitudinis on the rhizosphere microbial communities. Root knot nematodes are one of the most destructive hemibiotrophic root pathogens that can cause ginger bark cracking disease in ginger planting areas around the world. There is an urgent need for sustainable alternatives methods, such as biological control. The nematicidal activity of Bacillus altitudinis AMCC1040 has been previously shown in vitro and in pot experiments. Here, field experiments were conducted to evaluate the biocontrol potential of Bacillus altitudinis AMCC1040 against ginger bark cracking disease, and to evaluate its ability to colonize the rhizosphere. In addition, we also evaluated its impact on the rhizosphere microbial communities. The results of biocontrol experiments demonstrated that the application of Bacillus altitudinis AMCC1040 can significantly inhibit nematode reproduction, inhibit root galling and reduce the severity of ginger bark cracking disease. In addition, Bacillus altitudinis AMCC1040 colonized steadily in ginger rhizosphere soil ranging from 5.08 to 5.49 Log 10 CFU g−1 soils. Compared with fosthiazate (One of the most commonly used nematicides in China), Bacillus altitudinis AMCC1040 performed better in terms of bio-safety. Meanwhile, the taxa enriched in Bacillus altitudinis AMCC1040 treatment were found in Actinobacteria , Gemmatimonadetes and Firmicutes. This study demonstrated that Bacillus altitudinis AMCC1040 have a strong potential to control ginger bark cracking disease in the field. These results provide strong support for further exploration of the application of Bacillus spp. as biocontrol agents to control root knot nematodes in many crops. Furthermore, the occurrence of ginger bark cracking disease described in this study will be of great help to future prevention and control measures. [ABSTRACT FROM AUTHOR]

Since sugarcane is a ratoon crop, genome analysis of plant growth-promoting bacteria that exist in its soil rhizosphere, can provide opportunity to better understand their characteristics and use of such bacteria in turn, may especially improve perennial crop productivity. In the present study, genome of two bacterial strains, one each of B. megaterium (BM89) and B. subtilis (BS87), isolated and reported earlier (Chandra et al., 2018), were sequenced and characterized. Though both strains have demonstrated plant growth promoting properties and enhanced in-vitro plant growth responses, functional annotation and analysis of genes indicated superiority of BS87 as it possessed more plant growth promotion attributable genes over BM89. Apart from some common genes, trehalose metabolism, glycine betaine production, peroxidases, super oxide dismutase, cold shock proteins and phenazine production associated genes were selectively identified in BS87 genome indicating better plant growth performances and survival potential under harsh environmental conditions. Genes for chitinase, d -cysteine desulfhydrase and γ-aminobutyric acid (GABA), as found in BM89, propose its selective utilization in defense and bio-control measures. Concomitant with better settlings' growth, scanning electron micrographs indicated these isolated and characterized bacteria exhibiting healthy colonization within root of sugarcane crop. Kegg pathways' assignment also revealed added pathways namely carbohydrate and amino acid metabolism attached to B. subtilis strain BS87, a preferable candidate for bio-fertilizer and its utilization to promote growth of both plant and ratoon crops of sugarcane usually experiencing harsh environmental conditions. [ABSTRACT FROM AUTHOR]

Pseudomonas chlororaphis subsp. aurantiaca strain JD37 is a plant growth-promoting rhizobacterium (PGPR), which has important biotechnological features such as plant growth promotion, rhizosphere colonization and biocontrol activities. In present study, the genome sequence of JD37 was obtained and comparative genomic analysis were performed to explore unique features of the JD37 genome and its relationship with other Pseudomonas PGPR: P. chlororaphis PA23, P. protegens Pf-5 and P. aeruginosa M18. JD37 possessed a single circular chromosome of 6,702,062 bp in length with an average GC content of 62.75 %. No plasmid was detected in JD37. A total of 5003 functional proteins of JD37 were predicted according to the clusters of orthologous groups (COGs) database. The JD37 genome consisted of various genes involved in plant growth promotion, biocontrol activities and defense responses. Genes involved in the rhizosphere colonization and motility were also found in the genome of JD37, suggesting the common plant growth-promoting traits in PGPR. The identified resistance genes (e.g. those related to metal resistance, antibiotics, and osmotic and temperature-shock) and secondary metabolite biosynthesis revealed the pathways for metabolites it produced. Data presented in present study further provided valuable information on its molecular genetics and adaptive capacity in the rhizosphere niche. [ABSTRACT FROM AUTHOR]

1-aminocyclopropane-1-carboxylic acid (ACC) is a strong metabolism-dependent chemoattractant for the plant beneficial rhizobacterium Pseudomonas sp. UW4. It is unknown whether enhancing the metabolic rate of ACC can intensify the chemotaxis activity towards ACC and rhizocompetence. In this study, we selected four promoters to transcribe the UW4 ACC deaminase (AcdS) gene in the UW4 ΔAcdS mutant. PA is the UW4 AcdS gene promoter, PB20, PB10 and PB1 are synthetic promoters. The order of the AcdS gene expression level and AcdS activity of the four strains harboring the promoters were PB20 > PA > PB10 > PB1. Interestingly, the AcdS activity of the four strains and their parent strain UW4 was significantly positively correlated with their chemotactic activity towards ACC, rhizosphere colonization, roots elongation and dry weight promotion. The results released that enhancing the AcdS activity of PGPRenable them to achieve strong chemotactic responses to ACC, rhizocompetence and plant growth promotion. [ABSTRACT FROM AUTHOR]

Methods for screening isolates of the nematophagous fungus, V. chlamydosporium, for their ability to colonize the surface of plant roots are described. Significant differences in the extent of colonization were observed in sterile conditions and in soil; plant species and cultivars also differed in their ability to support a selected isolate of the fungus. Although fungal density could be estimated using a semi-selective medium, it was not possible to separate differences in vegetative growth from differences in sporulation. There was a weak positive correlation between estimates of fungal density on the roots of plants grown in sterile conditions and the extent of hyphal growth measured by direct observation.