Prevalence in Egyptian soils of r leguminosarum biovar viceae and their physiological properties

ABSTRACT

A survey was carried out on the prevalence of indigenous Rhizobium leguminosarum in different Nile Delta soils of Egypt. In addition, 163 strains of this bacterium were isolated from nodules of faba bt-an [Vicia faba] plants grown in the 40 locations under investigation to study some physiological characteristics of the indigenous bacteria as well as to determine their capacity in N[2]-fixation. Results showed that R.leguminosarum is present in soil in relatively low numbers [ca. 10[3] cells g[-1]] being the highest in the heavy teatured soils. Faba bean plants collected from Ismailia governor ate generally beared the highest number of nodules on their root systems [average of 43 plant[-1]] while those taken from Qalubia produced the lowest number [9 plant[-1]]. Out of the 163 R.leguminosarum isolated, 98 [ca. 60%] were sensitive towards all tested antibiotics [neomycin, kanamycin and streptomycin] at the given concentrations, only 19 isolates [11.7%] could resist the presence of the three compounds even applied at the highest concentrations, in comparison with the control medium containing 0.01% NaCl, 89 isolates [55%] could not grow at a salt level of 1% or more, mean while only 3 isolates [2%] did survive at 6% NaCl. No visible growth was observed in 8% salted medium. 59 isolates [36.2%] failed to withstand temperature as high as 35° or more, while 62 strains did grow fairly up to 35°. Only 8 strains could resist 45° for die 7 days of incubation. The 163 isolates widely differed in their ability to jwovide faba bean plants with fixed nitrogen. They could be classified into five categories namly; ineffective, slightly, moderately, highly and very highly effective [5. 46, 51, 45 and 16 isolates respectively]