Abstract
The effects of bean (Phaseolus vulgaris L.) cultivars and Rhizobium strains on nodule senescence were studied under glasshouse conditions. Four common bean cultivars (Carioca 80, CNPAF-2234, Rio Tibagi and Negro Argel) were inoculated separately with four Rhizobium strains (C05, CNPAF 146, SEMIA 487 and V-23), and harvested at 35, 46 and 55 days after emergence. Nitrogenase activity, total N t ransported and ureide content in the xylem sap and number of pink nodules began to decline soon after flowering, showing an early process of nodule senescence. Nodule colour and texture, as well as the rates of acetylene reduction and N transported in the xylem sap at different harvests, were affected both by plant cultivar and Rhizobium strain, and the symbiotic combinations more promising for delayed nodule senescence showed a higher proportion of active pink nodules during the reproductive growth phase of the plants.
