Resistance to antibiotics and fungicides associated with symbiotic effectiveness of Rhizobium Phaseoli strains

Abstract

Experiments with Phaseolus vulgaris L. grown in sand irrigated with N-free nutrient solution were conducted to evaluate the mutagenic stability, infectivity, and N₂-fixing ability of R. phaseoli spontaneous mutants resistant to antibiotics and fungicides. There were variations on resistance levels among the Rhizobium strains to the different biocides. Loss of infective ability or decrease in efficiency for N₂ fixation observed for several mutants were not related to the type of antibiotic and fungicide nor to the different concentration used. Some mutant strains exhibited a higher N₂-fixing ability when compared to SEMIA 487 and SEMIA 492 which are being used by inoculant manufacturers. The mutant SEMIA 4002-ST₁ was mutagenically stable. The results support the idea about the possibility of using spontaneous mutants in ecological of Rhizobium as long as they have mutagenic stability and have no cross-resistance to the antibiotics.