Screening Rhizobium spp. strains associated with Gliricidia sepium along an altitudinal transect in Veracruz, Mexico

Abstract

In order to characterize Rhizobium strains naturally associated with Gliricidia sepium (Jacq.) Walp. and to determine their effectiveness for seedling inoculation, morphologic traits of G. sepium nodules and Rhizobium strains isolated from them, collected along on altitudinal transect (10—970 m above sea level) in northern Veracruz were studied. The Rhizobium strains isolated (three from each of eight sampling sites) were evaluated in terms of dry matter production, total nitrogen and nodulation capability on six month-old G. sepium seedlings inoculated under greenhouse conditions. Even though all isolated strains belong to the Hup+ group, differences in both morphological and physiological traits of nodules and Rhizobium strains were observed, associated to site elevation. Nodules from low elevation sites ( 500 m) were branched, with strains sensitive to salt. Thirteen strains (two from sites below 100 m and 11 from sites above 100 m) significantly increased seedling biomass, and nine of them also increased nitrogen content without negatively affecting the physiological nitrogen use efficiency (PEI) as compared to control seedlings. The relative effectiveness index (REI) of these Rhizobium strains varied between 2.0 and 2.4. However, no significant trend (r = 0.25) was found between PEI values of strains and site elevation. Nodular mass (NM) varied from 1.1 up to 1.7 mg dry weight with significant differences among strains, even though no significant elevational trend was found in this trait.