植物根际促生菌对3种土传真菌病害病原的抑制作用

【目的】获取促生同时可防治3种土传真菌病害(Fusarium oxysporum、Sclerotinia sclerotiorum和Rhizoctonia solani)的生防菌,并明确其抑菌效果。【方法】利用前期研究获得的17株促生菌,采用平板对峙法测定其对病原真菌的拮抗作用及对菌丝生长的抑制作用。【结果】可有效拮抗立枯丝核菌的生防菌有6株,其中促生菌株FX2和LM4-3的抑制率达73.82%;拮抗尖孢镰刀菌的生防菌有7株,其中FX2的抑制率达到66.81%;拮抗油菜菌核病菌的生防菌有4株,其中菌株LHS11的抑制率高达85.71%。菌株LHS11和JM170通过次生代谢物抑制病原真菌。所有的生防菌对病原菌的菌丝生长均有一定的抑制作用。【结论】筛选得到对3种真菌病害病原具有较好生防作用的菌株LHS11和FX2。     

植物根际促生菌的筛选及鉴定

【目的】植物根际促生菌(PGPR)和植物的互作关系往往不稳定,PGPR菌群有可能提高菌株对野外环境的适应性。为此,本文根据PGPR促生机制的多样性,从不同植物根际土壤进行了PGPR的筛选及鉴定。【方法】首先,按照固氮、解磷、解钾、拮抗6种常见病原真菌,同时能在植物根际定殖为基本初筛标准,然后在实验室条件下测定初筛菌株的多项促生能力(PGP),最后通过生理生化试验和16SrRNA基因序列分析对所筛菌株进行鉴定。【结果】从江苏扬州、盐城等地土壤样品筛选出14株PGPR,具有体外抑菌、产NH3、产IAA、产HCN、产嗜铁素、解磷、溶钾、固氮以及产抗生素等促生能力。分类鉴定结果显示:7株属于假单胞菌属(Pseudomonas)、3株属于类芽孢杆菌属(Paenibacillus)、2株为芽孢杆菌属(Bacillus)、1株为布克霍尔德氏菌属(Burkholderia)、1株为欧文氏菌属(Erwinia)。【结论】所筛细菌具有多种促生能力,且能在根际定殖,为进一步构建多功能PGPR广适菌群提供菌株资源。     

Induction of resistance against Cercospora leaf spot in safflower by seed treatment with plant growth-promoting rhizobacteria

Out of seven isolates of rhizobacteria, four strains including GBO-3, INR937a, INR937b and IPC-11 were selected as inducers of systemic resistance against Cercospora carthami and tested individually for biological control of different important seed-borne fungal pathogens. The level of control achieved by each rhizobacterium varied with the pathosystem studied. The isolates GBO-3, INR937a, INR937b and IPC-11 exhibited reduced disease intensity in terms of average number of leaf lesions as compared to untreated control in protection experiments against C. carthami. Micromobilised with rhizobacterium GBO-3, INR937a, INR937b and IPC-11 safflower seeds were grown under greenhouse and challenge inoculated with C. carthami were selected for estimation of lipoxygenase, polyphenylalanine ammonia-lyase, peroxidase, polyphenol oxidase and β-1,3 glucanase activities were estimated spectrophotometrically. Increase in all enzymes was detected in foliar extracts from plants at different stages after challenge inoculation.     

Evaluation of plant growth-promoting Rhizobacteria for their efficiency to promote growth and induce systemic resistance in pearl millet against downy mildew disease

Six strains of Plant growth promoting Rhizobacteria (PGPR) were tested for their ability to promote growth and induce resistance in pearl millet against downy mildew disease. All the PGRP strains showed a significant (P < 0.01) increase in growth promotion in laboratory as well as greenhouse conditions. Only two strains of Pseudomonas spp., UOM ISR 17 and UOM ISR 23, were capable of protecting pearl millet against downy mildew significantly. Pseudomonas UOM ISR 17 and UOM ISR 23 were able to offer 56.3 and 47.5%, respectively against downy mildew disease. When tested for the time gap needed to offer maximum protection, it was found that both the strains needed four days to offer maximum protection of 73.3% and 59.7%, respectively. While both the Acetobacter strains UOM Ab9 and Ab11 and Azospirillum strain UOM Az3 were able to promote growth and offered disease protection of 39.2, 22.3 and 17.40% respectively, they were not as efficient as the two Pseudomonas strains in protecting pearl millet against downy mildew. Maximum growth promotion was recorded by Pseudomonas spp. UOM ISR 17 with 33.9 cm height which was 44, 45, 42 and 46.8% more in height, fresh weight, dry weight and leaf area over the control which recorded 27 cm height, 8.1 g fresh weight, 2.1 g dry weight and 29 cm² leaf area, respectively.     

植物根际促生菌作用机制研究进展

植物在生长过程中可能会遭受许多生物和非生物因素胁迫,从而降低生物产量. 人们已知一些植物在不同因素的刺激诱导下,能系统化建立抵抗或忍受不利因素的机制,植物根际促生菌（PGPR）就是其中一类能定殖于根系并促进植物生长的细菌.本文对PGPR促生机制进行归纳和总结,系统阐述了诱导体系抗性和诱导体系产生忍耐力两大促生机制.PGPR的作用机制的多样性暗示着其可能在更多的农业生态系统中得到应用.     

强化龙葵富集镉根际促生菌的分离、筛选与鉴定

【背景】植物-微生物联合修复土壤重金属污染日渐兴起,获取与超富集植物高效互作的微生物是实现联合修复技术进步的关键。龙葵在镉农田污染修复中广泛应用。【目的】筛选可促进龙葵生长及富集镉的耐镉根际促生菌。【方法】从龙葵根际土分离耐镉菌株,筛选具有良好促生特性的菌株,水培试验考察镉胁迫下菌株对植物生长及镉富集能力的影响,确定可促进龙葵生长及富集镉的微生物菌株,通过生理生化特性和16S rRNA基因序列分析进行菌株的初步鉴定。【结果】分离得到NT1、AXY1、AW2和AW1四株强化龙葵富集镉促生菌,经鉴定分别为Lysinibacillus sp.、Beijerinckia fluminensis、Achromobacter animicus和Herbaspirillum huttiense。上述菌株均可有效促进龙葵生长,增加其株高和干物质积累,提高地上部镉富集量。其中,NT1可使株高、地上部干重分别增加31.33%和62.65%,AW2可使地上部镉富集量增加37.29%。【结论】筛选所得菌株可为提高植物修复效率提供实践依据,为研制田间施用生态功能菌剂做铺垫,用于农田镉污染的微生物-龙葵联合原位修复。     

Identification,characterization and optimization of phosphate solubilizing rhizobacteria (PSRB) from rice rhizosphere

Two billion people worldwide take rice (Oryza sativa L.) as a staple food. Phosphorus (P) and Nitrogen (N) are the major requirements of rice; although these are available in limited concentrations within rice growing regions. Among different types of Plant growth-promoting rhizobacteria (PGPR), Phosphate solubilizing rhizobacteria (PSRB) constitute an important class. These are known for plant growth promotion by enhancing P and N uptake. PSRB are nowadays used as biofertilizers to restore the soil health. Under the present investigation identification, characterization and optimization of phosphate solubilizing activity of these microbes at different pH, temperature and salt concentrations was carried out. Thirty-seven isolates were recovered from different regions of rice rhizosphere on Pikovskaya (PVK) agar among which 15 isolates were recovered from R.S. Pura, 12 isolates from Bishnah and 10 isolates were recovered from Akhnoor sector of Jammu, India. A prominent halo zone of clearance was developed around the colonies of 12 different isolates, indicating phosphate solubilization activity. Four distinct isolates were amplified, cloned and sequenced for taxonomic identification using 16S primers. The results indicated that PS 1, PS 2, PS 3, PS 4 were related to Pseudomonas aeruginosa, Bacillus subtilis strain 1, B. subtilis strain 2, B. subtilis strain 3, respectively. These strains when grown at a wide range of ecological factors showed maximum growth at pH between 6.8 and 8.8, temperature between 28 °C and 37 °C and salinity between 1% and 2%. Screening for phosphate solubilization activity revealed that the halo zone diameter formed by these isolates extended from 2.1 to 3.2 mm. The phosphate solubilizing efficiency (SE) ranged from 35.4 to 50.9 with highest value of 50.9 by PS4 and maximum P solubilization of 10.22 µg/ml was recorded by PS4 at 7th day. Phosphate solubilization activity of these identified PSRB strains can be utilized and explored in the rice growing belts of Jammu region which are deficient in phosphorus. MIC value for zinc sulphate heptahydrate in 12 isolates varied from 1 mg/ml to 6 mg/ml. Phosphate solubilization activity and MIC of these identified PSRB strains can be utilized and explored in the rice growing belts of Jammu region which are deficient in phosphorus.     

The effect of plant growth-promoting rhizobacteria on the phytoextraction of Cd and Zn by Brassica napus L.

The test strains Bacteroidetes bacterium (Ba), Pseudomonas fluorescens (Pf) and Variovorax sp. (Va) were selected in advance for their in vitro capability for growth promotion of rapeseed in the presence of increased concentrations of Cd, Cu, Pb and Zn in the medium. In the pot experiment, the strains were used for single Ba, Pf, Va or combined Ba + Pf, Ba + Va, Pf + Va, and Ba + Pf + Va inoculation of B. napus growing in contaminated soil from alluvial deposits. The positive effect of bacterial strains on plant growth was observed in vitro, but was not confirmed in situ in the contaminated soil, where the tested strains inhibited biomass production, rather than stimulating it. However, single inoculation with Ba significantly increased the chlorophyll content and K⁺ concentration in the leaves. The inoculation of rapeseed with Ba and Va strains was indicated to be the most promising combination for phytoextraction of Cd and Zn from contaminated soil. Combined inoculation with Pf+Va and Pf + Ba+Va significantly decreased the concentration of heavy metals in the roots of rapeseed. We conclude that suitable combinations of PGPR can control the metal uptake of B. napus, selectively increasing either metal extraction or metal stabilization in the rhizosphere and offering promising applications in soil remediation.     

Seed priming with co-flocs of Azospirillum and Pseudomonas for effective management of rice blast

A modified approach was adopted to develop co-flocs consisting of Azospirillum brasilense MTCC-125 and Pseudomonas fluorescens MTCC-4828. The results of our study revealed that both Azospirillum and Pseudomonas strains exhibited a higher survivability when embedded in the flocs. The survivability of the strains in co-floc was found to be higher when compared to the log phase vegetative cells in different inoculant carriers, spermosphere rhizoplane and rhizosphere. The co-floc treatment has also significantly increased the germination percentage and vigour index of rice. In the present study flocculation was found to play a major role in enhancing adhesion of both the strains to rice roots. The co-flocs were studied for their efficiency to induce resistance in rice crop against rice blast. The relative role of Azospirillum and Pseudomonas co-flocs in the induction of resistance against the phytopathogen was evaluated. It was found that when the activities of polyphenol oxidase, peroxidase and phenol were high and when the relative amounts of the sugars were low, the disease infestation was less and vice versa. The association of these compounds strongly implies their role as casual agents of induced resistance against Pyricularia oryzae.     

Biological control of the wheat root rot caused by Fusarium graminearum using some PGPR strains in Saudi Arabia

The aim of this study was to evaluate the efficacy of selected bacterial strains against the wheat soil‐borne pathogen Fusarium graminearum under greenhouse conditions. The most potent isolates were 3 isolates out of 18 isolates, which have numbers 3, 9 and 10 with in vitro inhibition index 42.5%, 41.3% and 46.3% respectively. Isolates 3 and 10 were selected for the following experiments. Isolates 3 and 10 were identified as Bacillus subtilis MAA03 and Pseudomonas fluorescens MAA10, respectively according to International Identification Keys and, confirmed by using Biolog system and 16S rDNA where the strains exhibited more than 99.5% sequence identity. Their close taxonomic relationship was further documented by phenotypic similarities. The using of B. subtilis and P. fluorescens separately or in mixture as biocontrol agent against F. graminearum on wheat significantly increased the final germination percent, the mean daily germination and germination index of wheat cultivar, while the mean germination time was significantly decreased relative to infested control. The final infection percent, the mean daily infection and infection index were decreased significantly, while the mean infection time was significantly increased relative to infested control. The use of P. fluorescens as biocontrol agent was the most efficient than B. subtilis or in mixture and the best treatment was seed coating. The application of B. subtilis and P. fluorescens separately or in combination significantly affected the growth parameters of wheat cultivar Tabuki, the root length was significantly increased in seed coating and seed soaking treatments, while non‐significantly decreased in case of soil drench treatment relative to infested control. Shoot length was significantly decreased in case of seed coating treatment relative to infested control. The shoot fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The root fresh and dry weights were significantly increased in seed coating and seed soaking treatments relative to infested control. The number of leaves was significantly increased in all treatments relative to infested control.     

Plant immune system activation is necessary for efficient root colonization by auxin-secreting beneficial bacteria

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Molecular analysis of a major locus for resistance to downy mildew in sunflower with specific PCR-based markers

Resistance of sunflower to the obligate parasite Plasmopara halstedii is conferred by specific dominant genes, denoted Pl. The Pl6 locus confers resistance to all races of P. halstedii except one, and must contain at least 11 tightly linked genes each giving resistance to different downy mildew races. Specific primers were designed and used to amplify 13 markers covering a genetic distance of about 3 cM centred on the Pl6 locus. Cloning and sequence analysis of these 13 markers indicate that Pl6 contains conserved genes belonging to the TIR-NBS-LRR class of plant resistance genes. Received: 9 April 2001 / Accepted: 10 August 2001     

Integration of plant growth-promoting rhizobacteria and chemical elicitors for induction of systemic resistance in mulberry against multiple diseases

Abstract

In mulberry (Morus alba L.), various individual strains of plant growth-promoting rhizobacteria (PGPR) and synthetic analogs of naturally occurring plant activators have demonstrated their potential to elicit induced systemic resistance (ISR) against either brown leaf spot (Cercospora moricola) or leaf rust (Cerotelium fici) diseases. However, these biological and chemical elicitors have not been evaluated so far against multiple infections of both these diseases which commonly occur during the post-rainy season. The present study was therefore aimed to assess the capability of PGPR strains and chemical plant activators, as individual and in integration, in elicitation of ISR against multiple infections. Three PGPR strains, Azotobacter chroococcum strain Azc-3, Bacillus megaterium strain Bm-1 and Pseudomonas fluorescens strain Psf-4, and plant activators, acetyl-salicylic acid (ASA), sodium salicylate (NaS) and 4-amino-n-butyric acid (ABA) were selected for the study. Under in vitro tests, all the plant activators up to 2000 ppm concentration exhibited their compatibility with the PGPR strains tested. Upon assaying of elicitors with plant-pathosystem, disease suppression was significantly (p = 0.05) high with integrated application of PGPR strains and plant activators when compared to their individual applications. All the elicitors at individual application varied in their response to multiple infections with the plant age. However, integration of Azc-3 + ASA provided greater suppression to multiple infections of brown leaf spot and leaf rust diseases during the entire growth period of mulberry plants. Thus, this combination of biological and chemical elicitors holds great promise to provide an effective ecofriendly alternative to the toxic chemical fungicides presently recommended for the control of brown leaf spot and leaf rust diseases in mulberry.     

Biological hardening of micropropagated Picrorhiza kurrooa Royel ex Benth., an endangered species of medical importance

Three plant growth-promoting rhizobacteria viz. Bacillus megaterium, B. subtilis and Pseudomonas corrugata were used for biological hardening of micropropagated plantlets of Picrorhiza kurrooa. The bacterial isolates antagonized the fungal spp. postulated to cause death of micropropagated plants in plate-based assays and positively influenced survival and growth parameters in greenhouse investigation.     

A novel bacteriocin, thuricin 17, produced by plant growth promoting rhizobacteria strain Bacillus thuringiensis NEB17: isolation and classification

AIMS: The aim of this study was to identify and characterize a compound produced by the plant growth promoting bacterium, Bacillus thuringiensis non-Bradyrhizobium Endophytic Bacterium 17. METHODS AND RESULTS: The bacterial peptide was analysed and purified via HPLC. Using the disk diffusion assay this peptide inhibited the growth of 16/19 B. thuringiensis strains, 4/4 Bacillus cereus strains, among others, as well as a Gram-negative strain Escherichia coli MM294 (pBS42). Both bactericidal and bacteristatic effects were observed on B. cereus ATCC 14579 and bactericidal effects were observed on B. thuringiensis ssp. thuringiensis Bt1267. The molecular weight of the peptide was estimated via SDS-PAGE and confirmed with Matrix Assisted Laser Desorption Ionization Quadrapole Time of Flight mass spectrometry; its weight is 3162 Da. The peptide is biologically active after exposure to 100 degrees C for 15 min, and within the pH range 1.00-9.25. Its activity disappeared when treated with proteinase K and protease, but not with alpha-amylase or catalase. CONCLUSIONS: We conclude that this is the first report of a bacteriocin produced by a plant growth promoting rhizobacteria (B. thuringiensis) species and have named the bacteriocin thuricin 17. SIGNIFICANCE AND IMPACT OF THE STUDY: Our work has characterized a bacteriocin produced by a plant growth promoting bacterium. This strain is previously reported to increase soya bean nodulation.