ASSESSMENT OF N2 FIXATION BY THREE Arachis pintoi ECOTYPES USING THE ISOTOPE DILUTION TECHNIQUE

Abstract

The nitrogen derived from N2 fixation was measured by the 15N isotope dilution method, in three Arachis pintoi (Ap) ecotypes: CIAT 17434, 18744 and 18748, using a Bradyrhizobium strain (BS) CIAT 3101, and native strains (NS) from Veracruz, Mexico, on greenhouse conditions. The reference plants were: a non-nodulating Arachis hypogaea, Brachiaria arrecta, Brachiaria brizantha and Cynodon nlemfuensis. Plant material received a 15N-enriched solution at 5 atom % 15N. Five harvests were done, where dry matter yield was highest (Pï‚£0.001) in Ap ecotypes+BS (53.9 ±5.2 g pot-1), vs Ap ecotypes+NS (19.7 ± 0.7 g pot-1). N yield (mg pot-1) of Ap ecotypes+NS was: 439 ± 19.6 mg pot-1 vs 1538 ± 117.0 mg pot-1 (Pï‚£0.001) from Ap ecotypes+BS. Values of atom% 15N in excess of legume shoots were lower (0.027 ± 0.01) with BS, compared to NS group (0.052 ± 0.002). The proportion of N2 fixed was greater than 0.5 in the three Ap ecotypes+ BS, using grasses as reference plant. Arachis pintoi ecotypes CIAT 17434 and CIAT 18744 fixed more N than ecotype CIAT 18748; and the improved Bradyrhizobium strain CIAT 3101 was more efficient to fix N2 than the native strains.