The authors wish to acknowledge the European Commission for their support to the ENDEGRADE project (EU PROJECT: QLK3- CT2000-00164). DvdL and ST are presently being
supported by Laboratory Directed Research and Development funds at the Brookhaven National Laboratory under contract with the U.S. Department of Energy.

Endophytic Bacteria and Their Potential Applications

Endophytic and epiphytic bacteria were isolated from two soybean cultivars (Foscarin and Cristalina). Significant differences were observed in bacterial population densities in relation to season of isolation, soybean growth phase and the tissues from which the isolates were obtained. The isolates were identified by partial 16S rDNA sequence analysis, with most of the isolates belonging to the Pseudomonaceae, Burkholderiacea and Enterobacteriaceae groups. The potential of the isolates for plant growth promotion was evaluated by screening for indoleacetic acid (IAA) production and mineral phosphate solubilization; 34% of endophytic bacteria produced IAA and 49% were able to solubilize mineral phosphate whereas only 21% of epiphytic bacteria produced IAA although 52% were able to solubilize mineral phosphate. A high frequency of IAA producing isolates occurred in the early ripening Foscarin cultivar whereas a high percentage of phosphate solubilizing isolates were obtained from plants in the initial development stage (V6). We also found that 60% of endophytic and 69% of epiphytic isolates that produced IAA and solubilized mineral phosphate were also able to fix nitrogen in vitro. The soybean-associated bacteria showing characteristics related to plant growth promotion were identified as belonging to the genera Pseudomonas, Ralstonia, Enterobacter, Pantoea and Acinetobacter.

Isolation and characterization of soybean‐associated bacteria and their potential for plant growth promotion

Bacteria Used in the Biological Control of Plant-Parasitic Nematodes: Populations, Mechanisms of Action, and Future Prospects

Patterns of potential C source utilization by microbial communities were tested as a means for differentiating among and within rhizosphere samples of different crops. Utilization of 95 separate sole C sources was determined by inoculating microbial suspensions into BIOLOG plates and quantifying color production from a redox-sensitive dye. Suspensions were produced by shaking excised root samples from wheat, white potato, soybean and sweetpotato grown in hydroponic culture within controlled environmental growth chambers. Distinctive patterns of C source utilization were apparent for each crop type, and the differences among crops were consistent for experiments repeated over 2 years. A temporal shift in C source utilization related to plant development state was observed in soybean. Results indicate that this rapid method is effective for detecting plant dependent differences in rhizosphere communities, and changes in response to plant developmental state.

Patterns of potential C source utilization by rhizosphere communities

/pdf/bacteria-in-agrobiology-crop-ecosystems-4itmo41pw2.pdf

Bacteria in Agrobiology: Crop Ecosystems

Populations of rhizosphere microflora of plants which have demonstrated an antagonism toward phytopathogenic nematodes, including velvet bean (Mucuna deeringiana), castor bean (Ricinus communis), sword bean (Cannavalia ensiformis), and Abruzzi rye (Secale cereale)., were compared to the rhizosphere microflora of soybean. Population densities of total bacteria were significantly lower for young Abruzzi rye, mature velvet bean, and mature castor bean, and fungi from mature velvet bean than for soybean. Population densities of spore-forming bacilli were significantly higher for Abruzzi rye than for soybean. Population densities of coryneform bacteria for mature sword bean and velvet bean were significantly higher than for soybean. All seedling test poants supported significantly higher population densities of chitinolytic fungi than soybean. On mature plants, chitinolytic bacteria were significantly higher on all test plants except velvet bean. Populations of endophytic root bacteria for three of the four test plants were significantly higher than for soybean. Fifty randomly, selected bacterial strains from seedlings and mature plants of soybean and each test plant were characterized for various physiological traits associated with rhizosphere competence, including chitinolytic activity, gelatin hydrolysis, production of hydrogen cyanide, starch hydrolysis, phenol oxidation, siderophore production, and production of antifungal compounds (inhibition ofPythium ultimum and/orRhizoctonia solani). There was a strong trend to increased frequency in each of the physiological tests with bacteria from test plants in comparison to those from soybean. The frequency of starch hydrolysis was up to 24 times greater for strains from test plants than for soybean strains, and siderophore production was up to 22 times more frequent for test plants. These results demonstrate that, compared to soybean, plants with properties antagonistic to phytopathogenic nematodes have a distinct rhizosphere microflora.

Analysis of populations and physiological characterization of microorganisms in rhizospheres of plants with antagonistic properties to phytopathogenic nematodes

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Analysis of populations and physiological characterization of microorganisms in rhizospheres of plants with antagonistic properties to phytopathogenic nematodes