COMPARISON OF ANTIBIOTIC RESISTANCE PROFILE FOR THE ANALYSIS OF RHIZOBIA STRAINS NODULATING PEANUT ROOTS

BOGINO, P., BANCHIO, E., RINAUDI, L. Y GIORDANO, W.

Córdoba

Congreso; XV Jornadas Científicas de la Sociedad de Biología de Córdoba; 2005

Sociedad de Biología de Córdoba

Rhizobia are symbiotic bacteria that elicit on the roots of specific legume hosts the formation of new organs (nodules), within which the bacteria proliferate, differentiate into bacteroids, and subsequently fix atmospheric nitrogen into ammonia. Peanut (Arachis hypogaea L.) is usually nodulated by native or indigenous Bradyrhizobium spp. Our objectives of the present work were to evaluate the native peanut-nodulating strains of rhizobia in soils of Argentina and to study the diversity of these strains by using their intrinsic antibiotic resistance. Resistance patterns of the isolates to six antibiotics were used to group Bradyrhizobium strains. In general, strains analyzed were sensitive to gentamicin. Spontaneous mutants of peanut bradyrhizobia resistant to gentamicin 80 m g/ml were selected from strains used as inoculant of Bradyrhizobium sp., such as C-145, USDA 4438 and USDA 3180. These were used to evaluate the validity of using antibiotic-resistant mutants to make inferences about the competitiveness of inoculant strains in soil environments. In addition the effect of inoculation of peanut seed with Bradyrhizobium sp. C-145, USDA 4438 and USDA 3180 was determined under laboratory conditions. Results obtained showed significant differences in nodule number and plant dry biomass when peanut seeds were inoculated with the strain C-145. This strain with resistance to gentamicin (C-145 GmR) was selected to determine the competitive ability compared with native rhizobia. The use of spontaneous mutants resistant to antibiotic is a useful marker to evaluate the nodule occupancy after inoculation of peanut grown in soils with indigenous bradyrhizobial populations.