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Concatenated sequence analysis with 16S rRNA, rpoB and fusA genes identified a bacterial strain (IRBG74) isolated from root nodules of the aquatic legume Sesbania cannabina as a close relative of the plant pathogen Rhizobium radiobacter (syn. Agrobacterium tumefaciens). However, DNA:DNA hybridization with R. radiobacter, R. rubi, R. vitis and R. huautlense gave only 44%, 5%, 8% and 8% similarity respectively, suggesting that IRBG74 is potentially a new species. Additionally, it contained no vir genes and lacked tumour-forming ability, but harboured a sym-plasmid containing nifH and nodA genes similar to those in other Sesbania symbionts. Indeed, IRBG74 effectively nodulated S. cannabina and seven other Sesbania spp. that nodulate with Ensifer ( Sinorhizobium)/ Rhizobium strains with similar nodA genes to IRBG74, but not species that nodulate with Azorhizobium or Mesorhizobium. Light and electron microscopy revealed that IRBG74 infected Sesbania spp. via lateral root junctions under flooded conditions, but via root hairs under non-flooded conditions. Thus, IRBG74 is the first confirmed legume-nodulating symbiont from the Rhizobium ( Agrobacterium) clade. Cross-inoculation studies with various Sesbania symbionts showed that S. cannabina could form fully effective symbioses with strains in the genera Rhizobium and Ensifer, only ineffective ones with Azorhizobium strains, and either partially effective ( Mesorhizobium huakii) or ineffective ( Mesorhizobium plurifarium) symbioses with Mesorhizobium. These data are discussed in terms of the molecular phylogeny of Sesbania and its symbionts. [ABSTRACT FROM AUTHOR]

Abstract: A screenhouse experiment was conducted to evaluate the effects of inoculation with Meloidogyne javanica (uninoculated nematode control, low level [1000 eggs pot−1] and high level [10,000 eggs pot−1]) and rhizobial strains (uninoculated rhizobial control, strains KFR 647 and MBS1312) on nematode infection, nodulation and growth of Sesbania sesban (L.) Merr. (sesbania) provenances (Kisii and Kakamega). Heavy nematode infection of sesbania was noted for all three rhizobial inoculation treatments 2 months after sowing, and nodulation and plant growth were affected negatively at the high nematode inoculum level. Shoot dry weights showed negative and positive relationships with nematode infection (gall index) and number of effective rhizobium nodules, respectively. At 3 months, negative effects of the high nematode inoculum level on nodulation and plant growth were observed for rhizobial strain KFR 647 and the uninoculated control, but not for strain MBS 1312. Low nematode inoculum levels did not negatively affect nodulation or plant growth. The two sesbania provenances had similar growth at the high nematode inoculum level, but the Kisii provenance showed better growth than the Kakamega provenance at the low nematode inoculum level. [Copyright &y& Elsevier]