Characterization of rhizobia isolated from some tree legumes growing at the Karachi University campus

Rhizobial isolates from nodules of Albizia lebbeck (L.) Benth., and Samanea saman (Jacq.) Merr., were alkali-producing, slow growing and with monotrichous flagella, whereas, those from Pithecellobium dulce (Roxb.) Benth., and Dalbergia sissoo Roxb., were acid-producing and fast growers. Isolates from R dulce showed amphitrichous flagella, while lophotrichous flagella were found in the isolates of D. sissoo. Rhizobial isolates from D. sissoo and P. dulce utilized all the I I sugars used as carbon source, whereas isolates from A. lebbeck utilized 8, and those of S. saman utilized 7 out of 11 sugars. All isolates belonging to Mimosoideae were susceptible to Gentamycin, Neomycin and Tetracycline, but were resistant to Cephalexin, whereas reaction against other antibiotics was variable. Isolates of D. sissoo were resistant against Amoxicillin, Ampicillin, Cloxacillin, Erythromycin, Neomycin and Sulphamethoxazole Trimethoprim and susceptible against Gentamycin and Tetracycline.