ELISA evaluation of the competitive abilities of two Rhizobium meliloti strains

Abstract

The double antibody sandwich enzyme-linked immunosorbent assay (DAS-EL1SA) was used to determine the competitive abilities of Rhizobium meliloti strains BALSAC and NRG-185 which are used in commercial alfalfa inoculants for eastern and western Canada, respectively. The ratio of NRG-185:BALSAC in the inoculum applied to aseptically grown alfalfa (Medicago sativa L.) was adjusted to 0:100, 1:99, 50:50, 90:10, 99:1, or 100:0. The ratios between nodules containing only the BALSAC strain and nodules containing only strain NRG-185 were similar to their respective inoculum strain ratios. Nodules containing both strains occurred only with the inoculum strain ratio of 50:50. Total plant weights were highest with the two single strain inocula and were decreased 5–19% with dual strain inoculation. The decrease in total plant weight was significantly correlated with decreases in nodule number and nodule weight. The results suggest that R. meliloti strains BALSAC and NRG-185 have equal competitive abilities, but are somewhat antagonistic, resulting in decreased nodulation and plant growth when both are present in an inoculum.