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

Fifty common bean genotypes were cultivated in two separately field trials at the research station of Islamic Azad University, Khorasgan Branch during 2008-2009. The 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. The dose of Rhizobium for seed inoculation was 7 miligrams of bacteria for 1 kilogram of seed. The second experiment was control. The second experiment was analyzed in the same way as the first except for biological nitrogen fixation. The results showed definite positive and significant correlation in percentage of nitrogen fixation 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 fixation percent. Path analysis indicated that total nitrogen percentage in shoot, number of nodules per plant and biomass yield have direct and positive effect on nitrogen fixation 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 fixation capability in common bean genotypes.