Fate of GM rhizobial inoculants: lessons from Europe and elsewhere

摘要

The nitrogen-fixing symbiosis between leguminous plants and bacteria of the Rhizobiaceae has been exploited in agriculture for millennia. Commercial rhizobial inoculants, applied to legume seed where insufficient compatible rhizobia are present in soil, have been available for over a century. Their agronomic importance, familiarity and the relatively good knowledge of their biology and genetics, has made rhizobia a target for improvement by genetic manipulation (GM). For example, Sinorhizobium meliloti genetically modified to increase nitrogen fixation was field-tested in the USA in 1994 and given commercial approval by the US Environmental Protection Agency in 1997. In a programme of research funded by the EU, survival in the field of Rhizobium leguminosarum biovar viciae inoculants marked by GM has been monitored since 1987. At Rothamsted, populations declined sharply in the months following application but then stabilised although at two other sites the same inoculant could not be detected the year following application. Dispersal from the inoculation site was consistent with root growth and soil movement due to ploughing and no genetic interactions between the inoculant and native strains was detected in the field. There was evidence that the symbiotic plasmid of R. leguminosarum biovar viciae (which carries genes for host plant nodulation and nitrogen fixation) confers a survival advantage in the rhizosphere of both host and non-host plants. These observations are compared to results from other releases of GM rhizobia in Europe and the USA.