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Abstract
Faba bean is one of the most important legumes in Egypt and it considered as the common diet for most Egyptian people because it contains essential protein. Moreover, faba bean plants are rely on biological nitrogen fixation for get its nitrogen requirements in association with Rhizobium.
Biological nitrogen fixation by legumes is the results of a symbiotic relationship between the host plants and rhizobia. Rhizobia elicit the formation of specialized organs called nodules on their host. Symbiotic nitrogen-fixation by Rhizobium sp is controlled by many biological, harsh chemical and physical conditions. Biological factors including the host plant genotype, the rhizobia strain, the interaction of symbionts, predators and microorganisms which have antagonistic activities towards rhizobia. The physical and chemical factors include temperature, moisture, salinity, soil pH, nutrient deficiency, fertilizers, heavy metals and pesticides. This thesis aimed to study the competition between two isolates of Rhizobium leguminosarum biovar viceae. These isolates were isolated from soil in Egypt (strain S) and soil in Yemen (strain E). Also this study was extended to study the effect of specific phages and fungicide on the competition between the tow strains.
In addition to that, fungicide-resistant strains were isolated and the effect of phages on the competition between both strains was studied. Indigenous Rhizobium in soil, which specific for faba bean may be less efficient than applied strains as inoculants. Hence, these applied strains must be posses the high ability to compete the native rhizobia in soil and it must be tolerant for stress conditions such a biotic and biotic factors. Presence of rhizobiophage is considered as the more dangerous biotic factor which limit survival of rhizobia in soil and consequently reduced their numbers. Also, rhizobiophage has a indirect affect on succeeding of nodulation via increasing the phage tolerant rhizobia, but they mostly are non-efficient for nitrogen fixation. Also, Rhizobium effected by fungicides which commonly used for protection the legume seeds from fungi disease.