Isolation and Characterization of Sorghum Rhizosphere Bacteria Capable of Inhibiting Germination of Striga hermonthica (Del.) Benth Seed

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Ibrahim Osman Basher, Noha
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A study was carried out with the following objectives: 1- Isolation of sorghum rhizosphere bacteria that could be used as bio-control agents for Striga hermonthica. 2- Development of application methods to test the efficiency of the bacterial isolates as inhibitors of Striga hermonthica seed germination and suppressers of seedling emergence. 3- Identification and general characterization of the efficient isolates that inhibit striga seed germination. Fifteen soil samples were collected from the rhizosphere of 10 sorghum cultivars grown in two locations: eleven samples from Shambat (Fac. of Agric., University of Khartoum: Botanical garden and glass house) and four samples from Elgadaref region in Eastern Sudan to isolate bacteria capable of inhibiting Striga hermonthica seed germination. Fifty-four bacterial isolates were obtained using routine methods of isolation. The efficacy of the isolates was tested for inhibiting Striga hermonthica seed germination in preliminary in vitro experiments. Out of the 54 isolates, 20 (13 from Shambat and 7 from Elgadaref) showed good inhibitory effect to striga seed germination compared to the control when applied at a dose of 5 μl of bacterial suspension. Four isolates that showed very good inhibitory effect to striga seed germination beside their promotion of sorghum growth were tested in plastic bags experiments to evaluate the efficacy of these isolates in inhibiting striga seed germination and seedlings emergence. Three application methods were used; namely, coating sorghum seeds with bacterial suspension, direct application of bacterial suspension on sorghum seeds and shaking sorghum seeds with bacterial suspension. Number of striga / sorghum plant, shoot and root fresh weight, shoot and root dry weight and root: shoot ratio were used to evaluate the efficacy of isolates in promotion of sorghum growth. There were significant differences between the isolates efficiency. Coating sorghum seeds with the bacterial suspension, using gum arabic as carrier, were the best application method. This method was used to evaluate the efficiency of 20 isolates in another plastic bags experiment. The 20 isolates gave good inhibitory effect to striga seed xvi germination. On the basis of microbiological and biochemical tests, which are commonly used for identification of bacteria, the 20 isolates were found to belong to the genus Bacillus and within the genus to the species Bacillus coagulans, B. cereus, B. subtilis, B. licheniformis, B. stearothermophilus, B. amyloliquefaciens, B. circulans and B. thuringiensis