Sesbania-Rhizobium Specificity and Nitrogen Fixation

Abstract

The compatibility of potentially nitrogen fixing associations between ten Rhizobium strains and six Sesbania accessions (species) was studied under glasshouse conditions. The rates of N₂ (C₂ H₂) fixation (u moles C₂ H₄ /plant/h) were determined. The various Sesbania accessions responded differently to inoculation with the strains tested. The ANOVA test revealed that there are real accessions (P = 0.01) and strains (P = 0.05) differences. In general the results obtained indicated that the highest mean rate of N₂ (C₂ H₂) fixation and the highest degree of compatibility with strains under test was shown by Sesbania bispinosa (accession BA12). Sesbania grandiflora (accession GL 2.02) ranked next. The performance of Sesbania pachycarpa (accession PCI), Sesbania macrantha (accession MNI), and Sesbania sesban (accession SBIO) in the N₂ (C₂ H₂) assay is lower than that of accessions BAI2 and GL2.02, thus indicating the possibility of lack of compatibility between these three accessions and almost all of the Rhizobium strains studied. Plants of Sesbania rostrata (accession RSI) produced either extremely low or no ethylene (C₂ H₄) quantities in the N₂ (C₂ H₂) assay thus indicative of high specificity or that this legume is not promiscuous at all. However, inoculated and fertilized Sesbania rostrata performed quite satisfactorily and formed profuse N₂-fixing nodules on roots and stems when grown in potted soil under Central Saudi Arabia climatic conditions. The results obtained indicated high variability among treatments in nodule number.