Initial nodulation in seven bean cultivars inoculated with two Rhizobium strains

Abstract

Early nodulation and maintenance of nodule activity after common bean (Phaseolus vulgaris L.) flowering can favor higher N₂ fixation rates with the culture. Consequently, we have tried to identify the potential of induction of rhizobial nodulation genes and the potential of attraction of rhizobia to roots of seven bean cultivars inoculated with two Rhizobium strains. Differences were found among symbioses in relation to the exudation of nod-gene-inducing compounds by the host plant and in relation to the synthesis of molecules, by the Rhizobium, responsible for the increase in the number of root hairs. These two parameters were positively related to higher nodulation and N₂ fixation rates. All cultivars have shown good adhesion of rhizobia recovering, in average, 0.72% to 8.61% of initial inoculum, respectively on the primary and secondary roots. The recovery of cells on the secondary roots of cultivars with light-brown or yellow seed coat was ten times higher than in the primary root, indicating a good potential for secondary nodulation. The best symbiotic performances were achieved by cultivars Carioca and ESAL-580 and the worst by IAPAR-20 and Rio Tibagi.