Genetic Improvement of Biological Nitrogen Fixation in Common Bean Genotypes (Phaseolus vulgaris L.)

Fift y common bean genotypes were cultivated in two separately fi eld trials at the research station of Islamic Azad University, Khorasgan Branch during 2008-2009. Th e experimental design was randomized complete block. Bean seeds were inoculated by Rhizobium legominosarum biovar Phaseoli isolate L-109 in one of the experiments before sowing. Th e dose of Rhizobium for seed inoculation was 7 miligrams of bacteria for 1 kilogram of seed. Th e second experiment was control. Th e second experiment was analyzed in the same way as the fi rst except for biological nitrogen fi xation. Th e results showed defi nite positive and signifi cant correlation in percentage of nitrogen fi xation with some other been characters. Step-wise regression designated that total nitrogen percentage in shoot, number of nodules per plant and biomass yield accounted for 93.8% of variation expect for nitrogen fi xation percent. Path analysis indicated that total nitrogen percentage in shoot, number of nodules per plant and biomass yield have direct and positive eff ect on nitrogen fi xation index. Hence, total nitrogen percentage in shoot, number of nodules per plant and biomass yield are promising indirect selection criteria for genetic improvement of nitrogen fi xation capability in common bean genotypes.