Advantages of streptomycin resistant mutants in competition and survival of Rhizobium Phaseoli in commercial peat

Abstract

Survival and competitive abilities of spontaneous mutants of R. phaseoli resistant to antibiotics were studied by means of inoculation in commercial nonsterile and irradiated peat (5 Mrad of gamma radiation). There was a high number of microorganisms (actinomycetes and protozoa) antagonistic to Rhizobium in nonsterile peat and irradiation contributed to a better growth and_ survival of Rhizobium, which after 180 days remained with a number of agriculturally viable cells above 10 ⁸ .The death rates during storage at 5°C of the streptomycin resistant mutants were smaller than those of spectinomycin resistant mutants, specially in the nonsterile peat. Other experiments carried out with nonsterile peat confirmed a better survival of the mutants' to streptomycin in comparison to those resistant to spectinomycin and novobiocin, even when inoculated both together and at rates ten times lower. The results demonstrate the advantageous use of mutants in studies involving the action of biotic and abiotic factors on Rhizobium survival in nonsterile peat.