THE SESBANIA ROOT SYMBIONTS SINORHIZOBIUM-SAHELI AND S-TERANGA BV SESBANIE CAN FORM STEM NODULES ON SESBANIA-ROSTRATA, ALTHOUGH THEY ARE LESS ADAPTED TO STEM NODULATION THAN AZORHIZOBIUM-CAULINODANS
C. Boivin et al., THE SESBANIA ROOT SYMBIONTS SINORHIZOBIUM-SAHELI AND S-TERANGA BV SESBANIE CAN FORM STEM NODULES ON SESBANIA-ROSTRATA, ALTHOUGH THEY ARE LESS ADAPTED TO STEM NODULATION THAN AZORHIZOBIUM-CAULINODANS, Applied and environmental microbiology, 63(3), 1997, pp. 1040-1047
Sesbania species can establish symbiotic interactions with rhizobia fr
om two taxonomically distant genera, including the Sesbania rostrata s
tem-nodulating Azorhizobium sp. and Azorhizobium caulinodans and the n
ewly described Sinorhizobium saheli and Sinorhizobium teranga by. sesb
aniae, isolated from the roots of various Sesbania species, A collecti
on of strains from both groups were analyzed for their symbiotic prope
rties with different Sesbania species, S. saheli and S. teranga bv. se
sbaniae strains were found to effectively stem nodulate Sesbania rostr
ata, showing that stem nodulation is not restricted to Azorhizobium, S
inorhizobia and azorhizobia, however, exhibited clear differences in o
ther aspects of symbiosis, Unlike Azorhizobium, S. teranga bv. sesbani
ae and S. saheli did not induce effective stem nodules on plants previ
ously inoculated on the roots, although stem nodulation was arrested a
t different stages. For Sesbania rostrata root nodulation, Sinorhizobi
um appeared more sensitive than Azorhizobium to the presence of combin
ed nitrogen, S. saheli and S. teranga bv. sesbaniae were effective sym
bionts with all Sesbania species tested, while Azorhizobium strains fi
xed nitrogen only in symbiosis with Sesbania rostrata. In a simple scr
eening test, S. saheli and S. teranga bv. sesbaniae were incapable of
asymbiotic nitrogenase activity. Thus, Azorhizobium can easily be dist
inguished from Sinorhizobium among Sesbania symbionts on the basis of
symbiotic and free-living nitrogen fixation, The ability of Azorhizobi
um to overcome the systemic plant central appears to be a stem adaptat
ion function, This last property, together with its host-specific symb
iotic nitrogen fixation, makes Azorhizobium highly specialized for ste
m nodulation of the aquatic legume Sesbania rostrata.