HOST-SPECIFICITY AND CHARACTERIZATION OF FAST-GROWING RHIZOBIA FROM MACROPTILIUM-ATROPURPUREUM CV SIRATRO IN PAKISTAN

The growth characteristics, intrinsic antibiotic resistance pattern, utilization of different C sources and symbiotic characteristics of 18 fast-growing rhizobial strains isolated from root nodules of Macroptilium atropurpureum (Siratro) were studied. Colonies on agar at 2-3 days were large, gummy, translucent and spreading (2-4 mm dia) and were acid producing. These strains did not utilize sodium citrate as a sole source of C and were sensitive to low concentrations of chloramphenicol (25 mu g ml(-1)), tetracycline (8 mu g ml(-1)) and streptomycin (12 mu g m(-1)). The host specificity and effectiveness of these strains on different legume hosts revealed that they are different from other fast-growing strains. All strains failed to nodulate Glycine max (soybean cv. William, Lee and Peking). Sixteen of the isolates nodulated Leucaena leucocephala (ipil-ipil) and all 18 nodulated Phaseolus vulgaris (common bean). The fast-growing strains showed varying degrees of effectiveness in N-2 fixation on M. atropurpureum, Vigna mungo (blackgram) and V. unguiculata (cowpea). The isolates formed ineffective symbioses on two genotypes of V. radiata (mungbean).