COMPARISON BETWEEN BREEDING METHODS TO ENHANCE NITROGEN FIXATION IN THE COMMON BEAN (Phaseolus vulgaris L.)

Abstract

The common bean productivity can be improved by the increment of its capacity of nitrogen fixation in the symbiosis with bacteria of genus Rhizobium. This study had the objective to compare two breeding methodologies - F2 derived lines (LDF2) and single seed descent (SSD) in a cross among the cultivars Negro Argel (good Symbiotic N2 fixer) and Rio Tibagi (poor symbiotic N2 fixar) conducted with Rhizobium inoculation or mineral nitrogen. Eighteen families were selected on F4 in the LDF2 method based on nitrogen content in the grains and at the SSD method sixty seeds were carried out to F5 without selection. Families selected on F4 generation (LDF2) were superior for N2 fixation potential and grain yield in comparison with families that were conducted without selection (SSD) bean families selected in the F4 generation under mineral nitrogen treatment showed a tendency to respond less to inoculation then families selected under Rhizobium treatment. Furthermore, families selected under Rhizobium treatment showed better response when grown under the mineral nitrogen treatment. The same tendency was observed for families which respond to both sources of nitrogen. In this study was observed that selection under Rhizobium pressure provide a opportunity to plant breeders to select bean genotypeswith enhance nitrogen fixation potential and high grain yield.

KEY-WORDS: Nodulation; total N; grain yield.