Response of spring wheat (Triticum aestivum) to interactions between Pseudomonas species and Glomus clarum NT4

The effects of interactions between pseudomonads (Pseudomonas cepacia strains R55 and R85, P. aeruginosa strain R80, P. fluorescens strain R92, and P. putida strain R104) and the arbuscular mycorrhizal fungus Glomus clarum (Nicol. and Schenck) isolate NT4, on spring wheat (Triticum aestivum L. cv. Laura), grown under gnotobiotic and nonsterile conditions, were investigated. Although plant growth responses varied, positive responses to pseudomonad inoculants generally were obtained under gnotobiotic conditions. Shoot dry weight enhancement ranged from 16 to 48%, whereas root enhancement ranged from 82 to 137%. Shoot growth in nonsterile soil, however, was unaffected by pseudomonad inoculants, or reduced by as much as 24%. Shoot growth was unaffected or depressed by G. clarum NT4 whereas early root growth was enhanced by 38%. Significant interactions between the pseudomonad inoculants and G. clarum NT4 were detected. Typically, dual inoculation influenced the magnitude of response associated with any organism applied alone. The effect of these pseudomonads on G. clarum NT4 spore germination was investigated. Germination was inhibited when spores were incubated either on membranes placed directly on bacterial lawns of strains R85 and R104 (i.e., direct assay), or on agarose blocks separated from the bacteria by membranes (i.e., diffusion assay). When the agarose blocks were physically separated from the pseudomonad (i.e., volatile assay), there was no evidence of inhibition, suggesting that a nonvolatile, diffusible substance(s) produced by both strains R85 and R104 may inhibit G. clarum NT4 spore germination. Received: 11 December 1995     

青贮玉米促生菌的鉴定及生物学特性的研究

根据布坎南.R.E等著《伯杰细菌鉴定手册》（第八版）,对4株青贮玉米促进菌进行鉴定。结果表明,4株促生菌分属于短芽胞杆菌（Bacillus brevis),蜡质芽孢杆菌（Bacillus cereus）,放射形土壤杆菌（Agrobacteria radiobacter）和假单胞杆菌（Pseudomonas sp）。此餐,还对4株促生菌的生物学特性进行了比较观察。     

Isolation and identification of the most efficient plant growth-promoting bacteria associated with canola (Brassica napus)

 Thirteen of the most abundant Gram-negative bacteria which are able to grow in N-depleted culture conditions were isolated from the rhizoplane and endorhizosphere of canola (Brassica napus) and identified by 16S rDNA sequence analysis. Eight of these bacteria induced a significant increase in root dry weight ranging from 11 to 52%. Phylogenetic positioning based on 16S rDNA sequences indicated that at least four genera are represented, Pseudomonas, Variovorax, Agrobacterium and Phyllobacterium. The most important direct plant growth-promoting-rhizobacteria effect was found with both isolates belonging to the Phyllobacterium. Received: 18 April 2000     

Fresh-weight measurements of roots provide inaccurate estimates of the effects of plant growth-promoting bacteria on root growth: a critical examination

Four strains of plant growth-promoting bacteria (PGPB), including three strains of Azospirillum and Pseudomonas fluorescens 313 were used to inoculate seeds of wheat, tomato, pepper, and cotton. Inoculated seedlings were grown to the two or three-leaf stage. After harvest, seven different environmental and technical conditions were evaluated to determine the effect of these conditions on the reproducibility of fresh and dry root weight measurements. Dry root weight of each sample showed no significant variations (smaller than 1%), despite the variations in measurement conditions. Root fresh weights varied greatly (usually in the range of 4-10%, but up to 18%), and were significantly affected (P≤0.05) by air temperature and relative humidity, air currents, different light intensities during extraction of plants from the substrate, duration of the extraction from soil (depending on the size of the experiment and type of plant growth substrate), and the type of absorbing paper used to blot excess water from harvested roots. Measurements by different technicians did not influence fresh or dry weight values. We conclude that fresh weight determinations are altered by factors independent of the intended experimental variables and should not be used to evaluate the effect of PGPB on plants.     

Suppression of Meloidogyne javanica by Pseudomonas aeruginosa IE-6S in tomato: the influence of NaCl, oxygen and iron levels

Understanding the environmental factors that influence the suppression of disease-suppressive strains of Pseudomonas fluorescens is an essential step toward improving the level and reliability of their biocontrol activity. A 0.8 M NaCl concentration was optimal for in vitro survival and growth of IE-6S⁺ while, nematicidal activity by IE-6S⁺ was maximal when the bacterium was exposed to 0.4 M NaCl. The bacterium was highly sensitive to high (1.6 M) NaCl concentration. Culture filtrate of the bacterium resulting from the medium supplemented with 0.2 or 0.4 M NaCl showed the presence of secondary metabolite, hydrogen cyanide (HCN). Soil amendment with IE-6S⁺ alone or in conjunction with up to 0.8 M NaCl enhanced bacterial efficacy towards Meloidogyne javanica, the root-knot nematode. Soil amendment with NaCl up to 0.8 M also resulted in enhanced bacterial rhizosphere colonization and growth of tomato seedlings. Protein content of the shoot was reduced when soil was amended with 1.6 M NaCl. Inner root establishment of the bacterium was greatly affected in the soils treated with 1.6 M NaCl. Under in vitro conditions, IE-6S⁺ showed enhanced growth when kept at ambient oxygen conditions while the growth of bacterium affected when incubated at low oxygen conditions. Culture filtrate of the bacterium resulting from low oxygen level caused greater mortality of M. javanica juveniles in vitro compared with the filtrates obtained from ambient oxygen conditions. Culture filtrate from low oxygen conditions also showed the presence of hydrogen cyanide while those from ambient oxygen condition did not. Under glasshouse conditions, regardless of bacterial application, nematode penetration rate was greater when the pots were watered from the top; nematode penetration was lowered in bacterized pots compared with non-bacterized controls. IE-6S⁺ applied in the pots either watered from the top or bottom had no significant impact on growth of tomato but protein contents of the leaves increased after treatment with the bacterium. Rhizosphere and inner root colonization of the bacterium increased when the pots were watered from the top. Under in vitro conditions, with an increased iron concentration in the form of FeEDDHA, growth of IE-6S⁺ and its nematicidal activity increased. Culture filtrate of IE-6S⁺ obtained from liquid King's B medium supplemented with 0.5 or 1.0 mM FeEDDHA showed the presence of HCN. Under glasshouse conditions, soil treated with FeEDDHA alone did not reduce nematode penetration rates but did reduce greatly when applied in conjunction with IE-6S⁺. FeEDDHA applied at 0.5 mg/kg of soil in combination with IE-6S⁺ significantly enhanced plant growth and leaf protein contents. FeEDDHA at 1 mg/kg of soil increased bacterial populations both in the rhizosphere and inner root tissues of tomato.     

Replant diseases: Bacterial community structure and diversity in peach rhizosphere as determined by metabolic and genetic fingerprinting

Peach tree replant disease, though reported on in the literature for more than two centuries, has yet to have its causes clearly defined. Decline in peach productivity has been attributed to toxic agents, insects, nutritional disturbances, spray residues, fungi and nematodes. Bacteria has also been indicated as a contributing factor.Peach replant disease was reproduced by using two successive cultures on the same soil. Bacterial communities were isolated and characterized from healthy and diseased peach trees. The potential role of cyanide production by rhizobacteria in the replant problem of peaches was studied. Culture-dependent (evaluation of the number of culturable bacteria, metabolic activities, Biolog^® GN2) and independent (ribosomal intergenic spacer analysis, RISA) methods were used, in order to compare bacterial community structure and diversity in healthy and sick soils and to evaluate the possible role of cyanide.Bacterial densities were significantly increased in sick soils. Metabolic activities (Biolog^® GN2) and genetic structure, observed through RISA, were also significantly modified in sick soils. Changes in the composition of individual microbial groups in the rhizosphere of peach trees excavated from healthy or sick soil indicated the involvement of rhizobacteria in the etiology of the replant sickness of peach soil. More than 60% of the strains isolated from healthy soils corresponded to Pseudomonas sp. and 58% of the isolates from sick soils were Bacillus sp. This study determined that Bacillus were able to produce in vitro HCN. It also appeared that in sick soil, there was a shift in the structure of bacterial communities with an increase noted in phytotoxic microorganisms capable of producing HCN compounds.     

Evaluation of functional diversity in rhizobacterial taxa of a wild grass (Saccharum ravennae) colonizing abandoned fly ash dumps in Delhi urban ecosystem

Metal rich fly ash dumps may serve as repository of ecologically useful multi-functional rhizobacteria having potential use in the development of vegetation at the dumps. Therefore, in the present study bacteria from the rhizosphere of a wild perennial grass colonizing Indraprastha and Badarpur fly ash dumps of Delhi region were purified, identified and functionally characterized. The fly ash had low levels of nutrients, moisture and organic matter coupled with toxic levels of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). Both the dumps were mostly barren except for a few patches of Saccharum ravennae and some weedy species. Sixty five dominant, morphologically distinct rhizobacteria were purified, which belonged to 18 genera and 38 species. Gram-positive bacteria were dominating in the fly ash environment. Bacillus spp. and Paenibacillus spp. were common at both the dumps. Multi-metal tolerance was shown by diverse bacterial taxa. The minimum inhibitory concentration (MIC) was highest for As (12.5-20.0 mM) and Pb (7.5-10.0 mM), although many rhizobacteria also possessed significant tolerance to Cr, Zn, Ni, Cu, Co and Cd. The tolerance profiles of rhizobacteria to different metals may be ranked in the decreasing order as As > Pb > Cr > Zn > Ni > Cu > Co > Cd > Hg. Majority of rhizobacteria showed good siderophore activity. Multiple-metal tolerance was also coupled with high siderophore production in some of the isolates (Microbacterium barkeri IPSr74, Serratia marcescens IPSr90 and IPSr82, Enterococcus casseliflavus BPSr32, Bacillus sp. IPSr80, Pseudomonas aeruginosa BPSr43 and Brochothrix campestris BPSr3). Most of the bacteria could grow on nitrogen-deficient medium. However, the dominant nitrogen-fixers reported from the rhizosphere of other Saccharum species were not detected. S. marcescens IPSr90 was the only rhizobacterium, which showed ACC-deaminase (ACCD) activity. Proportion of phosphate-solubilizing bacteria was high. Considerable improvement in the seedling establishment, plant weight and shoot length in rhizobacterial inoculated plants of S. ravennae in fly ash environment indicated the significance of rhizobacteria in its colonization and spread to the dumps. Representative rhizobacteria, with high MIC (for most of the metals) and good plant growth promoting (PGP) traits comparable to commercially useful bacterial inoculants were identified as S. marcescens IPSr82 and IPSr90, P. aeruginosa BPSr43, Paenibacillus larvae BPSr106, Arthrobacter ureafaciens BPSr55, Paenibacillus azotofixans BPSr107 and E. casseliflavus BPSr32. S. ravennae and some of these rhizobacteria may be potentially useful for the development of inoculation technologies for conversion of barren fly ash dumps into ecologically and economically productive habitats.     

促进小麦生长的根围细菌的筛选及初步鉴定

为探明从植物根围土壤中筛选到具有高效促生作用的细菌菌株的分类地位和促生效果,并为进一步的应用奠定基础。从33个供试土样中分离得到1 700多个细菌菌株,在小麦上进行了促进生长的筛选。经过初筛、复筛,并对数据进行相关分析,最终得到2株具有良好促生效果的细菌菌株ZX-7和ZX-9,菌株ZX-7和ZX-9处理的小麦根重比对照分别增加38.8%和26.1%,鲜重比对照分别增加26.9%和19.3%、株高比对照分别增加7.4%和3.9%。通过对其16S rDNA序列分析,两菌株初步鉴定为芽孢杆菌属(Bacillus)细菌。     

大豆根际细菌Ⅰ拮抗大豆根腐病菌研究

本研究从４１个土样中分离到大豆外根际细菌７２３株，根内细菌９４株。通过对病原菌Ｆ３，Ｗ１，Ｓ１的平板拮抗测定，得到拮抗菌２７９株对其中１５株根际细菌进行了温室防病试验，得到２株防病效果较好的菌株，其中ＢＨ１防病最高，对Ｆ３，Ｗ１，Ｓ２的防效分别为：６４。０％，６３．４％，３３．３％。     

The effect of plant-associative bacteria (Azospirillum and Pantoea) on the fruit quality of sweet pepper under limited nitrogen supply

This study investigates the influence of a commercial product, Biopron^®, consisting of the bacteria Azospirillum brasilense and Pantoea dispersa on sweet pepper fruits (Capsicum annuum L.) under limited N supply. When the N supply was reduced from 12 (control) to 7 mmol L⁻¹, the concentration of total-N in the fruits was significantly reduced in both inoculated and non-inoculated plants. The N supply or inoculation did not affect the dry matter content or fruit firmness, but non-inoculated fruit with low N showed a decrease in pericarp thickness and a significant increase in the color parameter a^* compared with the control. Under limited N, inoculation increased the concentration of citric, ascorbic and succinic acids in green fruit compared with non-inoculated fruit, which showed lower values than control fruit. At a later (yellow) stage of development, only succinic acid showed a response to inoculation. Fruit peroxidase (EC 1.11.1.7) activity in fruit of inoculated plants was lower than that observed for non-inoculated fruit grown at both high- and low-N. In contrast, in yellow fruit, total phenolic compounds were increased under N limitation, with no inoculation effect. Our study shows that the effect of plant associative bacteria is not directly related with the increased potential availability of nutrients for uptake, especially for fruit quality characteristics.