Article Abstract:
The effects of three winter cover crop treatments on the distribution of a soil population of Rhizobium leguminosarum bv. trifolii across different size classes of soil aggregates were studied. A heterogeneous distribution of the Rhizobium soil population across the different size classes of soil aggregates was noted, and the distribution was found to be influenced by cover crop treatment and sampling time. One interesting feature of R. leguminosarum distribution was the similar population densities between Rhizobium organisms in a legume cover crop soil and those in cereal soil.
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Article Abstract:
Extracellular nor intracellular products are not responsible for the aluminum tolerance of Rhizobium leguminosarum. This conclusion was based on experiments using strain UHM-5, a pSym- Exo- derivative of aluminum-tolerant R. leguminosarum bv. phaseoli strain CIAT899. It is known that bacterial extracellular polysaccharides (EPS) play a major role in preventing metal toxicity. However, the survival of UHM-5 in a medium containing high levels of aluminum, despite the lack of EPS, proves that it plays no role in the aluminum tolerance of R. leguminosarum.
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Article Abstract:
A study of two strains of Rhizobium leguminosarum biovar phaseoli and three other plant growth-promoting rhizobacteria (PGPR) shows that rhizobia have higher potential for maize and lettuce root colonization than rhizobacteria. Rhizobial root populations show a fresh weight of log 4.1 CFU/g on maize roots and log 3.7 CFU/g on lettuce roots four and five weeks after seeding, respectively, whereas the corresponding weights for PGPR are log 3.5 and log 3.0 CFU/g.
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