Rhizosphere Isolates Research Articles

Phytophthora species detected in the rhizosphere of Alnus glutinosa stands in the Floodplain Forests of Western Turkey

AbstractThe occurrence of Phytophthora species in Alnus glutinosa stands in the Karacabey and Iğneada floodplain forests was investigated. Twenty‐seven soil samples taken from the rhizosphere of declining trees (without bark symptoms) were baited for Phytophthora. In total, 311 Phytophthora isolates were obtained following culturing on selective medium. On the basis of the morphological characteristics and the ITS sequences of the rDNA, Phytophthora plurivora accounted for 83% of the rhizosphere isolates. In addition to P. plurivora, P. gonapodyides (9%), P. chlamydospora (3.8%), P. lacustris (2.5%) and P. aff. cactorum (2%) were isolated from the surveyed areas. No P. × alni was detected in the present work. This paper is the first to report the isolation of P. plurivora and P. aff. cactorum from the rhizosphere of Alnus species in Turkey.

Genome variations between rhizosphere and bulk soil ecotypes of a Pseudomonas koreensis population.

Bulk soil and rhizosphere are soil compartments selecting different microbial communities. However, it is unknown whether this selection also can change the genome content of specific bacterial taxa, splitting a population in distinct ecotypes. To answer this question we compared the genome sequences of 53 isolates obtained from sugarcane rhizosphere (28) and bulk soil (25). These isolates were previously classified in the Pseudomonas koreensis subgroup of the P. fluorescens complex. Phylogenomics showed a trend of separation between bulk soil and rhizosphere isolates. Discriminant analysis of principal components (DAPC) identified differences in the accessory genome of rhizosphere and bulk soil sub-populations. We found significant changes in gene frequencies distinguishing rhizosphere from bulk soil ecotypes, for example, enrichment of phosphatases and xylose utilization (xut) genes, respectively. Phenotypic assays and deletion of xutA gene indicated that accumulation of xut genes in the bulk soil sub-population provided a higher growth capacity in a d-xylose medium, supporting the corresponding genomic differences. Despite the clear differences distinguishing the two ecotypes, all 53 isolates were classified in a single 16S rRNA gene OTU. Collectively, our results revealed that the gene pool and ecological behavior of a bacterial population can be different for ecotypes living in neighbouring soil habitats.

Improved growth and nutrient acquisition of wheat genotypes in phosphorus deficient soils by plant growth-promoting rhizospheric and endophytic bacteria

ABSTRACTIn this study, two bacterial strains were isolated from the rhizosphere and inside the roots of wheat (Triticum aestivum L.) plants growing in wheat land of Iran. Based on the 16s rRNA gene sequences, strains R185 and E240 were identified as Pseudomonas sp. (rhizospheric isolate) and Pseudomonas mosselii (endophytic isolate), respectively. Isolates were tested for traits that affect plant growth such as indole-3-acetic acid, siderophore, hydrogen cyanide production, and phosphate solubilization ability. Then the effect of strains on growth promotion, protein, nutrients of grains, and soil enzyme activity was investigated using a low-phosphorous soil under greenhouse conditions. Results revealed that significantly higher biomass accumulation and micronutrient assimilation were obtained in all the pots treated with bacterial strains as compared to the control. Co-inoculation of rhizospheric and endophytic bacteria improved the protein of grain by 11.3% (Marvdasht) and 9% (Roshan). Microbial inoculation had a positive effect on the concentration of P, Zn, and Fe in wheat grains. While inoculating wheat genotypes with a single rhizospheric strain increased dehydrogenase activity by 53.4%, this effect became stronger with increasing endophytic strain: up to 72% increase in soil dehydrogenase activity was observed in bacterial consortium treatment. Taken together, inoculation by rhizospheric–endophytic mix-strains with multi-plant growth-promoting traits could be a promising option to promote cereal quality.

Assessment of plant growth promoting activities of five rhizospheric Pseudomonas strains

Abstract Many strains form different species of genus Pseudomonas are proven as important plant growth promoting rhizobacteria, because of their ability to solubilization of nutrients, producing of different metabolites and enzymes, antimicrobial activities, etc. The five rhizospheric Pseudomonas stains were characterized and identified as potential plant growth promoting rhizobacteria (PGPR) in the present study. Substrates assimilation profile (API 20NE) and 16S rRNA gene nucleotide sequences were used for identification of the four strains rhizospheric isolates. The studied strains demonstrate the specific composition of activities associated with direct and indirect mechanisms of plant growth promotion. The strain Ps. putida BTCC1046 showed a complex of PGP-activities including ability for P-solubilization, production of phosphatases and lytic enzymes, siderophore production and activity against two bacterial phytopathogens. The other strain Pseudomonas sp. 1S4 is considered as bioagent with strong antifungal activity. The investigated Pseudomonas strains have the potential to be used in agriculture as bioagents.

Rhizospheric bacterial isolates of grass pea (Lathyrussativus L.) endowed with multiple plant growthpromoting traits.

The main aim of this work was to examine the plant growth promoting, biocontrol activities and stress competency of grass pea rhizobacterial strains from Ethiopia. Serial dilutions were carried out to isolate rhizobacterial strains from the rhizosphere soil samples. The isolates were characterized for their plant growth promoting, biocontrolling and stress tolerance potential. The isolates that showed better performance in the tested parameters were identified by 16S rRNA gene sequencing. Among the isolates tested on Pikovskaya agar medium, 22 isolates that showed solubilization index of >2·41cm were selected for further screening tests. Isolate AAUGPR-53 identified as Enterococcus species, Enterococcus casseliflavus strain showed the highest phosphate solubilization index and indole-3-acetic acid production efficiency of 4·81±0·02 (μgml-1 ) and 56·55±0·45 (μgml-1 ), respectively. Sixteen (72·7%) of the isolates showed invitro antifungal inhibition against Fusarium oxysporum f. sp. lentis with isolates AAUGPR-92 and AAUGPR-91 identified as Enterococcus species, E. casseliflavus strain and Enterococcus gallinarum strain exhibiting the highest inhibition of 83 and 78%, respectively. Likewise, 68·2%, 91·30%, 45·5%, 77·3% and 100% of the isolates produced chitinase, protease, cellulase, HCN and NH3 , respectively. Most of the isolates showed good tolerance to the tested stress factors. The 16S rRNA partial sequencing of the rhizobacterial isolates proved their taxonomic position in the existing bacterial isolates. The results indicated that three strains, AAUGPR-53, 91 and 92, that showed maximum sequence identity (99%) to Enterococcus species, E. casseliflavus and E. gallinarum were recommended as microbial inoculants for trials under greenhouse and field conditions. This study illustrates an effective alternative to conventional fertilizers that may contribute to crop disease reduction. Our results provide a foundation for future research that will lead to identifying potentially useful biocontrol strains found in the rhizosphere of grass pea.

Relative antagonistic potential of some rhizosphere biocontrol agents for the management of rice root-knot nematode, Meloidogyne graminicola

The relative effectiveness of twelve indigenous rhizosphere isolates of fungal and bacterial biocontrol agents (BCAs) was evaluated against rice root-knot nematode, Meloidogyne graminicola on rice cv. PS-5. The culture filtrates of BCAs significantly inhibited egg hatching and caused mortality to nematode juveniles. However, considerable variability was observed in the degree of virulence among different isolates/strains when tested in vitro. Six most efficient isolates/strains were selected to ascertain their effectiveness under pot condition. The BCAs were applied as soil application at 2 mL/pot (2–3.5 × 106 CFU/mL). Plants grown in the nematode inoculated soil developed terminal galls on roots and suffered 24–31% reduction in plant growth and yield. However, applications of BCA suppressed the negative impact of the nematode and subsequently increased plant growth and yield. Notably, application of Pseudomonas putida provided better control of root-knot disease, compared to rest of BCAs. The frequency of BCA colonization on eggs, juveniles and adult females of M. graminicola was highest with Trichoderma harzianum followed by Purpureocillium lilacinum. While these effects were minimal with Bacillus subtilis. However, the greatest build-up in the rhizosphere population was recorded with P. putida followed by P. fluorescens and T. harzianum. Our study revealed for the first time the antagonistic effect of P. putida against M. graminicola. Interestingly, the relative effectiveness of P. putida was found to be higher than P. fluorescens and P. lilacinum. In addition to these, we also observed T. harzianum to effectively suppress the M. graminicola, as an endophyte. Field trials under naturally infested plots validated the efficacy of P. putida and T. harzianum, and satisfactorily controlled M. graminicola with 60–74% enhancement in the tillering and yield of rice.

Multifunctional potential of endophytic and rhizospheric microbial isolates associated with Butia purpurascens roots for promoting plant growth.

The functional diversity of endophytic and rhizospheric microorganisms associated with the promotion of plant growth includes increased availability of plant nutrients, phytohormone synthesis and phytopathogen suppression. We used the hypothesis that the unknown root and rhizospheric community associated with the Butia purpurascens palm, an endemic species of the Cerrado, could be composed of microbiota with great functional diversity. Thus, the potential of the isolates of this community for four functional traits was evaluated: solubilization of calcium phosphate (CaHPO4) and iron phosphate (FePO4), synthesis of indoleacetic acid (IAA) and suppression of seed- and fruit-spoilage fungi of B. purpurascens. A total of 166 bacterial isolates, most belonging to the phylum Proteobacteria (94%), and 46 fungal isolates (Ascomycota) were tested. None of the isolates showed the four functional traits tested, but 72% presented two traits (CaHPO4 solubilization and IAA synthesis). Fifteen fungi (27% of the isolates) presented only the trace for IAA, whereas the capacity for antibiosis was observed in only eight bacteria. CaHPO4-solubilization capacity was evidenced by all bacterial isolates and by some fungal isolates. The functional trait for IAA production was present in all isolates, and production levels were significantly above 100μgmL-1 for some bacteria. Isolates of the genus Bacillus efficiently suppressed the growth of spoilage fungi tested, with relative inhibition rates reaching levels higher than 60% when using Bacillus subtilis. These results attest to the multifunctionality of the endophytic and rhizospheric isolates of B. purpurascens for the promotion of plant growth. This is the first study that sought to identify the root endophytic and rhizospheric microbiota associated with the B. purpurascens palm for the bioprospection of species with functional traits related to the promotion of plant growth, thus opening the way for in vivo tests in plants of commercial or ecological interest.

Trichoderma-Mediated Suppression of Red Rot of Sugarcane Under Field Conditions in Subtropical India

Thirty-eight isolates of Trichoderma spp. established from the rhizosphere of sugarcane were characterized using a multiplex PCR assay and further assessed for the production of hydrolytic enzymes chitinase and cellulase. The results of multiplex PCR assay successfully identified 29 isolates and revealed T. harzianum to be the predominant species (21 isolates) in sugarcane rhizosphere followed by T. longibrachiatum (8 isolates). In enzymatic assays, chitinase production was recorded in 18 isolates and cellulase production observed in 17 isolates. However, there was a considerable variability in both chitinase and cellulase production potential across the isolates. Three T. longibrachiatum isolates (STr-52, STr-83 and STr-108) exhibited high production of both chitinase and cellulase. Talc formulation of two promising isolates (STr-83 and STr-108) was prepared and evaluated in the field conditions for their potential to suppress red rot under three different delivery systems, viz. sett treatment, soil application and their combination. All Trichoderma treatments resulted in considerable reduction in red rot (29.5–56.3%) over untreated control. However, the level of reduction accorded was much higher when the Trichoderma isolates were applied as a combination of sett and soil treatment (> 53% reduction) as compared to soil application (43–49% reduction) or sett treatment alone (< 35% reduction). Delivery of Trichoderma isolates as a combination of sett and soil treatment also exhibited highest NMCs and yield over untreated control. The application methods of talc formulations of these two isolates offer a feasible and effective option for large-scale application of these isolates for the management of red rot disease in sugarcane growing regions.

The effect of Indole Acetic Acid producing rhizosphere bacteria isolated from forest soil on the seedling vigor, growth of host and non-host plants and host nutrition level of crops grown in different soils

Many rhizosphere microorganisms are capable of producing Indole Acetic Acid which enhances plant growth and they may be developed as biofertilizers to enhance the uptake of nutrients from nutrient poor soils. The direct effect of IAA would include improving seedling vigor and plant growth. Rhizosphere bacteria producing IAA were isolated from Maize, Cucumber, Chili and Soy bean to investigate their effect on nutrition of the host plants in different soils and the effect on seedling vigor and growth of host and non-host plants. Eight isolates from maize, four from cucumber and two each from Soy bean and Chili were obtained following using Salkowski method. They were Staphylococcus sp. (seven), Bacillus sp. (seven), Serratiasp. (one) and Pseudomonas sp. (one). The presence of IAA was confirmed with thin layer chromatography and was quantified using a colorimetric method. The effect on vigor and growth of isolates from different hosts on host and non-host plants was determined using a pot assay where they were cultivated in forest soil inoculated by mixing isolates from different hosts separately. The effect on seedling vigor was investigated also by conducting a glass tube experiment. A hydroponic assay was conducted by inoculating single strains on the roots of their respective host plants to assess their effect on nutrition. Each crop was inoculated with the rhizosphere isolates of the same crop in different soil types. The plants were analyzed for Nitrogen, Phosphorus, Potassium and chlorophyll. Maize isolates generally had a positive effect on vigor and growth of host and non-host plants. Although some pattern in effect was observed the results are irregular and unpredictable. The isolates from Maize, Soy and Cucumber increased the host nutrient levels. The effect of inocula varied with soil type. The highest nutrient absorption of host plants compared to the control was observed in nutrient poor soils. As such these microorganisms may be suitable as bioinoculants which enhance the plant nutrition in nutrient deficient soils. Therefore while IAA forming rhizosphere bacteria are good candidates as bioinoculants, great caution is required in their use the effect is different depending on the inoculum and soil type. Researching in holistic approach is recommended. Keywords: Auxin, Bio fertilizer, Salkowski, Nutrition, Soil

Sustainable management of soil borne pathogens of tomato

Tomato is the second most cultivated crop in world, which not only used in culinary but also has industrial and medicinal value. Tomato plants are susceptible to various soil borne diseases that severely affect its growth and fruit quality either grown in fields or cultivated in greenhouse under controlled conditions. The use of rhizospheric microorganisms as a biocontrol agent (BCA) against phytopathogens is considered as one of the most promising eco-friendly approach for sustainable management for tomato cultivation. The rhizopsheric microorganisms caters several mechanisms to control or suppress soil borne phytopathogenic fungi, bacteria and nematodes, via direct mechanism of mycoparasitism and/or indirect mechanisms such as antibiosis through production of secondary metabolites or antibiotics; and competition for nutrients and ecological niche. The present work outlines role of rhizospheric microbial isolates in management of phytopathogens affecting quantitative and qualitative production of tomato.

Use of Endophytic and Rhizosphere Actinobacteria from Grapevine Plants To Reduce Nursery Fungal Graft Infections That Lead to Young Grapevine Decline.

Endophytic and rhizosphere actinobacteria isolated from the root system of 1-year-old grafted Vitis vinifera plants were evaluated for their activities against fungi that cause grapevine trunk diseases. A total of 58 endophytic and 94 rhizosphere isolates were tested. Based on an in vitro bioassay, 15.5% of the endophytic isolates and 30.8% of the rhizosphere isolates exhibited antifungal activity against the fungal pathogen Diplodia seriata, whereas 13.8% of the endophytic isolates and 16.0% of the rhizosphere isolates showed antifungal activity against Dactylonectria macrodidyma (formerly Ilyonectria macrodidyma). The strains which showed the greatest in vitro efficacy against both pathogens were further analyzed for their ability to inhibit the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum (formerly Phaeoacremonium aleophilum). Based on their antifungal activity, three rhizosphere isolates and three endophytic isolates were applied on grafts in an open-root field nursery in a 3-year trial. The field trial led to the identification of one endophytic strain, Streptomyces sp. VV/E1, and two rhizosphere isolates, Streptomyces sp. VV/R1 and Streptomyces sp. VV/R4, which significantly reduced the infection rates produced by the fungal pathogens Dactylonectria sp., Ilyonectria sp., P. chlamydospora, and P. minimum, all of which cause young grapevine decline. The VV/R1 and VV/R4 isolates also significantly reduced the mortality level of grafted plants in the nursery. This study shows that certain actinobacteria could represent a promising new tool for controlling fungal trunk pathogens that infect grapevine plants through the root system in nurseries.IMPORTANCE Grapevine trunk diseases are a major threat to the wine and grape industry worldwide. They cause a significant reduction in yields as well as in grape quality, and they can even cause plant death. Trunk diseases are caused by fungal pathogens that enter through pruning wounds and/or the root system. Although different strategies have recently been developed to protect pruning wounds using antifungal compounds (natural or synthetic) or biocontrol agents, no tools are yet available for controlling soil pathogens that infect plants through their root system. This study shows that different actinobacterial isolates, when applied to grafts in a nursery, can significantly reduce the infection rate caused by fungal pathogens that enter through the root system. This is a new, promising, and green alternative for preventing the decline of young grapevines in nurseries and vineyards.

In vitro bacterization of banana (Musa spp.) with native endophytic and rhizospheric bacterial isolates: Novel ways to combat Fusarium wilt

Compared to conventional planting material, micropropagated plantlets are highly susceptible to Fusarium wilt because they are free from beneficial root inhabitants. We aimed to introduce mixtures of beneficial microbes in the plantlets in the rooting medium under in vitro conditions rather than by field applications. Endophytes and rhizobacteria from different banana cultivars and plantation areas were screened and characterized. Under in vitro conditions, banana tissue culture plantlets were bacterized with the prospective endophytes, Bacillus subtilis strain EPB56 and EPB10 and the rhizobacteria, Pseudomonas fluorescens strain Pf1 and effects of in vitro bacterization were investigated against Fusarium oxysporum f. sp. cubense race 1 under glasshouse and field conditions. Inoculation of bananas during micropropagation allowed for the omission of minerals and salts as well as vitamins from the growing media while resulting in plantlets close to double size compared to the controls with full strength media. All endophyte and rhizobacteria strains tested resulted in significant reductions in Fusarium infection in the glasshouse and field and in significantly better plant growth. The three-way combination of bacteria resulted in 78% disease reduction and more than doubled the yields compared to the untreated controls across two field experiments. Three-way inoculation led to yields of 23 and 24 kg/ bunch compared to chemical disease control (13; 15 kg/bunch) and untreated controls (10; 13 kg/bunch) in the two field experiments. Under glasshouse conditions, activity of defence enzymes was significantly increased by all inoculation treatments. Inoculation in vitro led to the establishment of the microorganisms in the plant system before delivering to the farming community. Micropropagation combined with the establishment of a beneficial microbial consortium should complement the micropropagated plants for easier adaptation under field conditions.

Mutualism between Klebsiella SGM 81 and Dianthus caryophyllus in modulating root plasticity and rhizospheric bacterial density

AimsDianthus caryophyllus is a commercially important ornamental flower. Plant growth promoting rhizobacteria are increasingly applied as bio-fertilisers and bio-fortifiers. We studied the effect of a rhizospheric isolate Klebsiella SGM 81 strain to promote D. caryophyllus growth under sterile and non-sterile conditions, to colonise its root system endophytically and its impact on the cultivatable microbial community. We identified the auxin indole-3-acetic acid (IAA) production of Klebsiella SGM 81 as major bacterial trait most likely to enhance growth of D. caryophyllus.MethodsipdC dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to D. caryophyllus roots and correlated to root growth promotion and characteristic morphological changes. SGM 81 cells were localised on and within the plant root using 3D rendering confocal microscopy of gfp expressing SGM 81. Using Salkowski reagent IAA production was quantified and localised proximal to roots in situ. The effect of different bacterial titres on rhizosphere bacterial population was CFU enumerated on nutrient agar. The genome sequence of Klebsiella SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships.ResultsInoculation of D. caryophyllus roots with Klebsiella SGM 81 drastically promoted plant growth when grown in agar and soil, concomitant with a burst in root hair formation, suggesting an increase in root auxin activity. We sequenced the Klebsiella SGM 81 genome, identified the presence of a canonical ipdC gene in Klebsiella SGM 81, confirmed bacterial production and secretion of IAA in batch culture using LC-MS/MS and localised plant dependent IAA production by SGM 81 proximal to roots. We found Klebsiella SGM 81 to be a rhizoplane and endophytic coloniser of D. caryophyllus roots in a dose dependent manner. We found no adverse effects of SGM 81 on the overall rhizospheric microbial population unless supplied to soil in very high titres.ConclusionKlebsiella SGM 81 effectively improves root traits of D. caryophyllus in a dose dependent manner, likely through tryptophan dependent IAA production in the rhizoplane and potentially within the intercellular spaces of root tissue. Under optimal plant growth promoting conditions in non-sterile soil, the high total microbial titre in the rhizosphere supports a mutualistic relationship between Klebsiella SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.

Functionality of Root-Associated Bacteria along a Salt Marsh Primary Succession.

Plant-associated bacteria are known for their high functional trait diversity, from which many are likely to play a role in primary and secondary succession, facilitating plant establishment in suboptimal soils conditions. Here we used an undisturbed salt marsh chronosequence that represents over 100 years of soil development to assess how the functional traits of plant associated bacteria respond to soil type, plant species and plant compartment. We isolated and characterized 808 bacterial colonies from the rhizosphere soil and root endosphere of two salt marsh plants, Limonium vulgare and Artemisia maritima, along the chronosequence. From these, a set of 59 strains (with unique BOX-PCR patterns, 16S rRNA sequence and unique to one of the treatments) were further screened for their plant growth promoting traits (siderophore production, IAA production, exoprotease production and biofilm formation), traits associated with bacterial fitness (antibiotic and abiotic stress resistance – pH, osmotic and oxidative stress, and salinity) and metabolic potential. An overall view of functional diversity (multivariate analysis) indicated that the distributional pattern of bacterial functional traits was driven by soil type. Samples from the late succession (Stage 105 year) showed the most restricted distribution, harboring strains with relatively low functionalities, whereas the isolates from intermediate stage (35 year) showed a broad functional profiles. However, strains with high trait performance were largely from stage 65 year. Grouping the traits according to category revealed that the functionality of plant endophytes did not vary along the succession, thus being driven by plant rather than soil type. In opposition, the functionality of rhizosphere isolates responded strongly to variations in soil type as observed for antibiotic resistance (P = 0.014). Specifically, certain Pseudomonas sp. and Serratia sp. strains revealed high resistance against abiotic stress and antibiotics and produce more siderophores, confirming the high plant-growth promoting activity of these two genera. Overall, this study contributes to a better understanding of the functional diversity and adaptation of the microbiome at typical salt marsh plant species across soil types. Specifically, soil type was influential only in the rhizosphere but not on the endosphere, indicating a strong plant-driven effect on the functionality of endophytes.

Integrated Nutrient Management for Improved Cauliflower Yield and Soil Health

ABSTRACTNutrient management in Cauliflower (Brassica oleracea var. botrytis L.) cultivation is in part dependent on the microbial population in the rhizosphere. Fertilizer must be applied to support plant growth and development. Whether fertilizer usage in cauliflower can be reduced needs to be determined. Rhizospheric isolates of cauliflower, obtained from soil around the roots and from their roots, in the low and mid-hills agro-ecological zones of India were tested for their efficacy to support cauliflower productivity. The plant growth–promoting rhizobacteria SB5, SB8, SB10, and SB11 exhibited the best plant growth–promoting traits with antagonism against soilborne pathogens compared to the reference strain Bacillus pumilus (JN559852). Application of SB11 (Bacillus spp.) exhibited the most plant growth–promoting attributes in field trials at 75% N and P and increased yield by 33% over the uninoculated control at 100% N and P. The isolate SB11 exhibited P solubilization, siderophore production, indole acetic acid production, hydrocyanic acid (HCN) production, and antifungal activity that may be developed as a plant growth–promoting rhizobacteria (PGPR) to enhance crop productivity and sustain soil health while saving 25% usage of chemical fertilizers.

Bacteria from wheat and cucurbit plant roots metabolize PAHs and aromatic root exudates: Implications for rhizodegradation

ABSTRACTThe chemical interaction between plants and bacteria in the root zone can lead to soil decontamination. Bacteria that degrade polycyclic aromatic hydrocarbons (PAHs) have been isolated from the rhizospheres of plant species with varied biological traits; however, it is not known what phytochemicals promote contaminant degradation. One monocot and two dicotyledon plants were grown in PAH-contaminated soil from a manufactured gas plant (MGP) site. A phytotoxicity assay confirmed greater soil decontamination in rhizospheres when compared to bulk soil controls. Bacteria were isolated from plant roots (rhizobacteria) and selected for growth on anthracene and chrysene on PAH-amended plates. Rhizosphere isolates metabolized 3- and 4-ring PAHs and PAH catabolic intermediates in liquid incubations. Aromatic root exudate compounds, namely flavonoids and simple phenols, were also substrates for isolated rhizobacteria. In particular, the phenolic compounds—morin, caffeic acid, and protocatechuic acid—appear to be linked to bacterial degradation of 3- and 4-ring PAHs in the rhizosphere.

In vitro screening of zinc solubilizing rhizospheric isolates for agrochemicals compatibility

In vitro screening of zinc solubilizing rhizospheric isolates for agrochemicals compatibility

Induction of systemic resistance (ISR) against sheath blight of rice caused by Rhizoctonia solani Kuhn using biological seed treatment with Trichoderma

Sheath blight caused by Rhizoctonia solani Kuhn has recently noticed one of the most important diseases of rice on almost all the high yielding varieties in major rice growing area. In our study morphologically and molecu-larly characterized thirty rhizospheric isolates of Trichoderma (T. harzianum and T. virens) from different locations of Uttarakhand were evaluated for their mycoparasitic ability, disease (sheath blight) suppressing potential and inducing systemic resistance against Rhizoctonia solani. Maximum inhibition in hyphal growth (58.9 %) against R. solani was recorded with isolate PB 2 followed by PB 3 (53.4 %) in confrontation assay. Under glass house con-dition, minimum disease severity (13.6%) was recorded in the treatment where seeds were treated with PB 22 and this treatment also exhibited highest total phenol content (394 ?l/g) 168 hours after pathogen inoculation. Total phenol content was also increased maximally (466 ?l/g) before pathogen inoculation in the treatment where seeds were treated with PB 22. Moreover, high quality ISR activity was recorded with isolates PB 21, 3, 1, 4, 23, 2 and 16 as they reduced more than 34 percent disease and total phenol contents 456 ?l/g, 449 ?l/g, 442 ?l/g, 440 ?l/g and 440 ?l/g, 438 ?l/g and 431 ?l/g were recorded for respective isolates indicated induction of resistance in paddy against sheath blight disease caused by R. solani.

Bacillus species as the most promising bacterial biocontrol agents in rhizosphere and endorhiza of plants grown in rotation with each other

In this study, a total of 550 cultivable bacterial isolates were isolated from rhizosphere and endorhiza of rice, Berseem clover, and oilseed rape grown in rotation with each other. The potential of antifungal activity of all isolates against five rice pathogenic fungi was investigated under in vitro conditions. Of 550 isolates, 139 inhibited the mycelial growth of at least one fungal rice pathogen. The results also showed that rhizosphere and endorhiza of every third plant (three studied plants) harbored the bacteria (139 isolates) with good potential for inhibiting fungal rice pathogens in vitro. Based on biochemical tests and by comparison of 16S rDNA sequences, of the superiors six endophytic and rhizosphere isolates, which showed strong inhibitory effects against the mycelial growth of all the five fungal rice pathogens (Magnaporthe oryzae, M. salvinii, Fusarium verticillioides, F. fujikuroi, and F. proliferum), were identified. Two isolates REN4 and CEN2, isolate CEN6, isolate CEN3, and two isolates REN3 and CEN5 were closely related to Bacillus mojavensis, B. amyloliquefaciens, B. subtilis, and B. cereus respectively. Strains REN4 and REN3 were obtained from rhizosphere and endorhiza of rice, while strains CEN6 and CEN2, and strains CEN5 and CEN3 were isolated from rhizosphere and endorhiza of clover and oilseed rape respectively. Therefore, it can be concluded that plants cultivated in rotation with rice and grown on the same soil harbor protective bacteria such as genus Bacillus and that may be potential reservoirs of bio-control agents for control of the rice pathogenic fungi tested in this study.

Isolation, identification, characterization, and screening of rhizospheric bacteria for herbicidal activity

The consistent application of agrochemical herbicides has been reported to impact negatively on human health, environment, and food safety, and facilitated the emergence of weed resistances. Rhizosphere bacteria (RB) of different crops were screened for antagonism against Amaranthus hybridus L. (pigweed) and Echinochloa crus-galli (L.) Beauv. (barnyard grass) using necrosis assay technique. A total of eight rhizosphere bacterial isolates (B1–B8) produced different degrees of leaf necrosis on target weeds with isolate B2 manifesting the most significant necrotic activity. The rhizospheric bacterium (B2) with the highest necrotic activity was identified using 16S rRNA sequencing technique and further investigated. Molecular, morphological, and biochemical characterizations confirmed B2 isolate to be Pseudomonas aeruginosa. On isolation with ethyl acetate, separation, defatting, purification, and flash chromatography, seven different fractions (fraction 1–fraction 7) were obtained out of which fraction 4 showed the highest necrotic activity in necrosis assay experiment. Preparative HPLC of fraction 4 resulted in a pure compound that completely inhibited seed germination and seedling development of pigweed and barnyard grass but remained non-antagonistic to other tested soil fungi used in this study. The result obtained from this present study consequently confirmed the antagonistic behavior of rhizosphere-inhabiting P. aeruginosa to the target weeds and qualified the suitability of bacterium as good alternative source of bioherbicide. Potential herbicidal formulation from P. aeruginosa will help reduce crop loss due to weed challenges while offering a partial solution to the use of agrochemicals and food security.