Specificity and competitiveness of rhizobium strains in Centrosema under controlled conditions

Abstract

Two green-house experiments with a sand-vermiculite substrate were conducted to compare the efficiency of 11 Rhizobium strains with three centrosema species (C. macrocarpum CIAT 5065, Centrosema sp GC 312/79, and an interspecific hybrid between C.pubescens, C.virginianum and C. brasilianum (Itaguaí hybrid), and to study the competitivity of four strains of Rhizobium in the Itaguaí hybrid, Strain C-106 isolated from C. pubescens was superior to the others in all centrosemas tested when inoculated as single strain. However, in the presence of strain C-551 (also isolated from C. pubescens) it did not cause the Itaguaí hybrid to nodulate, and formed only few nodules in a mixture with two other strains. The strain C-551, in spite of its low efficiency, has shown high competitiveness and formed from 70% to 100% of the nodules when inoculated in a mixture with three strains. Among the centrosemas studied, the Itaguaí hybrid was superior in nodulation, growth, and nitrogen fixation.