Summary
Roots of pea seedlings without lateral roots, inoculated with Rhizobium leguminosarum, were unable to support growth of the bacteria on the root surface. After the formation of lateral roots a strong increase of bacterial numbers on the root surface was observed. This increase was restricted to that part of the main root where lateral roots were present.
When pea seedlings were grown in Petri dishes with their roots on agar (carbon source present), mixed with a suspension of Rhizobium leguminosarum, no zone of stimulated bacterial growth was observed in the vicinity of the root. This was in contrast with seedlings of a number of other legumes which under the same experimental conditions gave a distinct zone of bacterial growth near the roots. Only where lateral roots emerged from the main pea root, a rather weak stimulation of the rhizobia was observed after some time.
Lateral roots of pea seedlings growing in sterile agar along the bottom of the Petri dish upon inoculation with Rhizobium leguminosarum gave a zone of bacterial growth. This zone started at some distance from the root, apparently owing to the presence of a zone of growth inhibition surrounding the roots more closely.
When seedlings of various leguminous plants were grown in tubes with their roots in agar, rhizobial growth occurred along the entire root system down to the bottom of the tube. Growth in the deeper parts of the agar was due to the release of oxygen by the roots. No promotion of growth was found near the roots of pea seedlings. in case the agar was supplemented with yeast extract or glutamic acid, pea plants also promoted the growth of Rhizobium in the vicinity of their roots but in contrast with other plant species used, the zone of promoted growth was not in direct contact with the root surface. re]19740124
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van Egeraat, A.W.S.M. The growth of Rhizobium leguminosarum on the root surface and in the rhizosphere of pea seedlings in relation to root exudates. Plant Soil 42, 367–379 (1975). https://doi.org/10.1007/BF00010012
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DOI: https://doi.org/10.1007/BF00010012