The invention is related to a symbiotic system comprising a plant of the Leguminosae family, and a bacterium of the rhizobium family, wherein in said bacterium a gene coding for a flavohemoglobin protein is over expressed. The present invention is also related to a method for delaying the senescence of symbiotic nodules, comprising inoculating a plant of the Leguminosae family with a bacterium of the rhizobium family, wherein said rhizobium overexpresses a gene coding for a flavohemoglobin protein. A method for cultivating a plant of the Leguminosae family is also disclosed.
