Symbiotic and Phenotypic Characteristics of Rhizobia Nodulaing Cowpea (Vigna Unguiculata L. Walp) Grown in Arid Region of Libya (Fezzan)

Abstract

Symbiotic and phenotypic characteristics of thirty rhiobial isolates obtained from root nodules of two cowpea (Vigna unguiculata L. Walp) cultivars that grow in different sites of Fezzan (Southern part of Libya) were studied. Cultural characteristics and cross-nodulation with Arachis hypogega and Faidherbia albida showed that they were slow-growing rhizobia. Each isolate was found to coexist with non-symbiotic bacteria similar in their cultural characteristics to fast-growing rhizobia. All isolates formed symbiosis with the test plants, but different in their nitrogen-fixation efficiency. Numerical analysis of phenotypic characteristics showed that at boundary level of 70% average similarity, the isolates formed four distinguished groups and two isolates remained separate. Most isolates exhibited wide tolerance to acidity, alkalinity and extreme temperatures. They also resistant to some heavy metals such as mercury, copper, zinc, lead, cadmium and aluminum at low concentrations and antibiotics like polymyxin, colistin, bacitracin and nalidixic acid. Isolates displayed different response to salinity ranging from sensitive, which unable to grow in 1% NaCl to resistant and grow at 2% NaCl or above. Urea was hydrolyzed by most of them and carbohydrates utilizations were different. Sucrose and maltose were metabolized by most of the test isolates, whereas, monosaccharide and sugar alcohols were poorly utilized.

Phenotypic and genotypic characteristics of cowpea rhizobia from soils of Ethiopia

“…In some nodules more than one kind of bacterial isolates were identified. This is in agreement with Abdelnaby et al (2015) in which multiple occupants of different rhizobial isolates were recovered from root nodule of cowpea in Egypt. Totally, 77 isolates were collected from pinkish/red color root nodules.…”

“…It is interesting to note that about 34% of isolates failed to induce nodule on the host legume and considered as cowpea root nodule endophytes. Several previous reports also showed the occurrence of non-rhizobial bacteria in the root nodule of cowpea (Sarr et al, 2010;Abdelnaby et al, 2015). Finally, a total of 40 indigenous cowpea rhizobial isolates that are representative of the different geographical locations of the country were selected for further study.…”

“…Cowpea rhizobia show distinct variations in their cultural and physiological characteristics, which have been used for identification and diversity studies. Fastgrowing and slow-growing isolates vary in their growth and colony characteristics (Jordan, 1982), tolerance to temperature, antibiotics, pH and salts (Zablotowicz and Focht, 1981;Florentino et al, 2010;Abdelnaby et al, 2015). Fast-growing cowpea rhizobial isolates are more tolerant to in vitro stresses than the slow-growing isolates (Leite et al, 2009;Abdelnaby et al, 2015).…”

“…Fastgrowing and slow-growing isolates vary in their growth and colony characteristics (Jordan, 1982), tolerance to temperature, antibiotics, pH and salts (Zablotowicz and Focht, 1981;Florentino et al, 2010;Abdelnaby et al, 2015). Fast-growing cowpea rhizobial isolates are more tolerant to in vitro stresses than the slow-growing isolates (Leite et al, 2009;Abdelnaby et al, 2015). Reports about versatility in utilization of C and N substrates by cowpea rhizobia are inconsistent (Hadad and Loynachan, 1985;Abdelnaby et al, 2015).…”

“…Fast-growing cowpea rhizobial isolates are more tolerant to in vitro stresses than the slow-growing isolates (Leite et al, 2009;Abdelnaby et al, 2015). Reports about versatility in utilization of C and N substrates by cowpea rhizobia are inconsistent (Hadad and Loynachan, 1985;Abdelnaby et al, 2015).…”