Dynamics of Rhizobium competition for nodulation of Pisum sativum cv. Afghanistan.

Nodulation of Pisum sativum cv. Afghanistan by Rhizobium leguminosarum strain Tom can be blocked by the nonnodulating R. leguminosarum strain PF2. This system was used to study the dynamics of rhizobial binding to seedling root surfaces. Appreciable numbers of 35S-labeled rhizobia bound to the root surface within 2h after inoculation. PF2 colonized the root surfaces earlier and in greater numbers that did Tom. Radioactive extracellular polysaccharides and lipopolysaccharides from either organism failed to bind to the seedling roots in measurable quantities.