Symbiotic Nitrogen Fixation in Dry Bean Cultivars

Abstract

Dry Beans (Phaseolus vulgaris L.), is the second-most important grain legume, and North Dakota has ranked first in dry bean production. The overarching research question of my project is whether we can increase the nitrogen (N) fixing potential of dry bean cultivars with inoculation and compare the nitrogen (N) fixing potential of common dry bean cultivars. Field experiment was conducted to compare peat and liquid inoculants during 2016 and 2017 growing seasons. In the field study, N2 fixation was estimated by stable isotope (15N) dilution technique. Liquid inoculant (70.5±5.9 kg ha-1) showed similar potential to the peat based inoculant (60.5±4.7 kg ha-1) for N2 fixation, however, inoculation treatments did not increase the N2 fixation over uninoculated (control). Further, it was investigated the nifH gene (marker for N2 fixation) expression in the dry bean-Rhizobium phaseoli symbiotic system. It was found that the relative normalized nifH gene expression significantly correlates (r = 0.82) with the total amount of N2 fixed, indicating the genetic control of symbiotic efficiency. Study on N-assimilatory genes, NR for nitrate reductase and GS for glutamine synthetase, showed that N2 fixation alone could not support plant N need in the later stages of growth (i.e. late flowering) and supplementary application of mineral-N is necessary for better plant growth and economic-yield. Dry bean cultivars did not response to inoculation and genetically, they differed significantly in N2 fixation potentials.