Classical and omic approaches to the analysis of acid-stressed alfalfa nodulating rhizobia.

DRAGHI, W. O.; DEL PAPA, M. F.; PISTORIO, M.; LOZANO, M. J.; GIUSTI, M. A.; TORRES TEJERIZO, G.; HELLWEG, CH.; WEIDNER , S.; NIEHAUS, K.; PÜHLER, A.; LAGARES, A.

Los Cocos, Córdoba-Argentina

Congreso; XXIII Reunión Latinoamericana de Rizobiología (RELAR 2007); 2007

Asociación Latinoamericana de Rizobiología

Alfalfa-nodulating rhizobia present in agricultural soils from Argentina and Uruguay: Diversity, acid tolerance, symbiosis, and genotypic characteristics.Soil acidity is a worldwide distributed stress-factor (von Uexküll y Mutert, 1995) that severely restricts rhizobial survival and symbiosis in agricultural soils (Glenn y Dilworth, 1994). Thus, diverse experimental approaches have been used to increase knowledge on the survival, persistence, and biology of rhizobia in the acid underground.In Argentina, large areas of arable lands have progressively acidified over the last 10 to 20 years, where the continuous cultivation over time without crop rotation are thought to be main factors that favored soil acidification.In central Argentina a gradual acidification of a significant proportion of cultured soils has been observed during the last 20 years. Such observation, together with the known sensitivity of Sinorhizobium mellioti to the hydrogen ions moved our laboratories to investigate the kind and characteristics of the alfalfa-nodulating rhizobia present in the acidic soils from Argentina and Uruguay. As a result, Del Papa et al. (1999) identified in the local soils the presence of two kinds of rhizobia: a major group represented by S. meliloti, and a second group geno/phenotypically related to the previously described Or191 isolate recovered from a soil of Oregon, USA. The Or191-like rhizobia recovered from our soils showed to be promiscuous, markedly acid tolerant, inefficient to fix atmospheric nitrogen, and highly competitive to nodulate alfalfa (Del Papa et al., 1999; Segundo et al., 1999; Wegener et al., 2001). Such evidences prompt us to investigate more deeply the symbiosis and ecology of such rhizobia in order to estimate both their evolution in local soils, and the impact on the population of efficient S. meliloti. Thus, we analyzed the