Characterization of Native Guar Rhizobia and Their Cross Inoculation Abilities Among Different Guar (Cyamopsis tetragonoloba (L.) Taub.) lines

Abstract

Nineteen Rhizobium isolates were extracted from the root nodules of different guar lines (Cyamopsis tetragonoloba (L.)Taub.) which were grown randomly on different soil samples collected from eleven different localities in Sudan. Eleven of the isolates were selected and authenticated as guar rhizobia. Cross–inoculation experiments showed a wide range in the degree of line x isolate efficiency. This was reflected by variations in number of nodules, shoot dry weight and nitrogen content produced by the same guar line when inoculated with different Rhizobium isolates. Results showed that the number of nodules produced was positively correlated with the dry weight of shoot and nitrogen content. Characterization of the isolates showed that, all of the tested isolates were fast–growing at 28°C, acid producers, don’t absorb Congo red, unable to grow on glucose peptone agar, microaerophilic and did not form endospores. The isolates were able to express Catalase, Oxidase and Tryptophane deaminase, but were not able to express Beta–galactosidase. The isolates were not able to produce Indole, 3–ketolactose and H2S. There is a wide range of variation in the abilities of the isolates to utilize Citrate and to express the enzymes Lysine decarboxylase, Urease, Arginine dehydrolase and Ornithine decarboxylase. All of the isolates were able to liquefy gelatin except isolate K 5. Variations were also observed in the abilities of the isolates to reduce Sodium selenite and to grow on different concentrations of Methyl red, Malachite green and Crystal violet. Considering carbohydrates utilization, all isolates were able to utilize most of the tested carbohydrates as sole carbon source. The isolate S12 was able to tolerate high salinity levels of up to 120 g /l. Considering antibiotic sensitivity a range of variation was observed among the tested isolates. With the exception of the isolates C4 and K 5, all of the isolates were sensitive to Nitrofurantion and were all sensitive to Tetracycline except for C4 and U 10. On the other hand all of the isolates were resistant to Polymyxin B sulfate except S12 and C4 which were sensitive to this antibiotic. Characterization and evaluation of the genetic diversity of Rhizobium isolates were performed using specific primers; the results showed the inability of the isolates D 7 and N 9 to yield PCR product with any of the used primers, although are authentic guar rhizobia. Total DNA from each isolate was digested with the restriction enzyme Hind III and fragments of similar sizes were obtained. This result may indicate true relationships between the guar rhizobia under study