Certain Environmental Factors Affecting Rhizobia and Symbiotic Systems

The interrelation between rhizobia and certain fungi, bacteria, actinomycetes, nematodes, and seed-coat diffusates of Phaseolus vulgaris were investigated. The effect of pesticides, i.e. fungicides, herbicides, and nematocides on growth of rhizobia and the symbiotic systems between rhizobia and their respective hosts is reported. Degradation of certain herbicides and insecticides is shown. The movement of rhizobia in soil as affected by water tension, tolerance of salts, and soil temperature are discussed.

Environmental factors may affect the successful establishment of an effective symbiosis between rhizobia and their hosts at any or all the three stages. They may 1) affect occurrence, growth, and survival of root nodule bacteria, 2) modify nodule formation, or 3) affect the function of the formed nodules (Vincent 1962).

The environmental aspects considered here include the antagonistic factors against rhizobia, the pesticides, and some ecological aspects of rhizobia in soil, e.g., the movement and salts and heat tolerance. These aspects were investigated by Egyptian workers over the period 1948–1972. Comprehensive reviews on the effect of environmental factors on rhizobia were reported by Vincent (1962) and Nutman (1972).

Die Beziehungen zwischen Rhizobien einerseits und Pilzen, Bakterien, Aktinomyceten, Nematoden und den Ausscheidungen aus der Samenschale von Phaseolus vulgaris andererseits werden besprochen. Die Wirkung von Pestiziden, z. B. Fungiziden, Herbiziden und Nematoziden, auf das Wachstum von Rhizobien und auf die symbiontischen Systeme zwischen Rhizobien und ihren Wirtspflanzen wird abgehandelt. Außerdem wird der Abbau einiger Herbizide und Insektizide gezeigt. Die Bewegung der Rhizobien im Boden wird auch unter Berücksichtigung von Wasserspannung, Salztoleranz und Bodentemperatur erörtert.