Variability for Biological Nitrogen Fixation Capacity in Beans

Authors: Cichy, Karen

Submitted to: Saginaw Valley Bean and Beet Farm Report
Publication Type: Experiment Station
Publication Acceptance Date: 4/1/2011
Publication Date: 6/1/2011
Citation: Cichy, K.A. 2011. Variability for Biological Nitrogen Fixation Capacity in Beans. Saginaw Valley Bean and Beet Farm Report. p. 60-63.

Interpretive Summary:

Technical Abstract: As legumes, common beans have the capacity to form a symbiotic relationship with soil bacteria called rhizobia and fix nitrogen from the atmosphere. Common beans however are considered to be poor nitrogen fixers as compared to other legumes. Identification of genetic variability for N fixation capacity is an important step to breed beans that require less nitrogen fertilizer. In this study dry bean lines of diverse origin were evaluated for their ability to fix nitrogen. Sixteen dry bean lines were planted in 2010 at the Saginaw Valley Research Farm under low fertility with two treatments: 1) rhizobium inoculum 2) no rhizobium inoculum. When the bean plants reached the stage of maximum aboveground biomass (mid pod fill), two plants per entry was harvested. Samples were oven dried and ground to a fine powder. These samples were analyzed for total nitrogen content and the ratio of stable nitrogen isotopes (15N and 14N). Since the 15N/14N ratio of nitrogen from the atmosphere (fixed) is lower than the ratio of N mineralized in the soil it is possible to use this method to determine the amount of nitrogen in a sample that originated from N fixation. One requirement to do this analysis is to include a plant that does not fix nitrogen in the experiment. In common beans, mutants have been identified which do not nodulate and therefore do not fix nitrogen. One such mutant was included in this experiment. It is R99, which is a mutant identified in the navy bean cv. OAC Rico. Variability for concentration of nitrogen in the shoot was observed among the cultivars. The average percent N of the shoot was similar (2.3%) under both the seed inoculated with rhizobium and the non inoculated seed. The bean variety with the highest nitrogen concentration in the shoot was Puebla 152. The average percent nitrogen derived from fixation was higher in the inoculated seed treatment (39%) as compared to non inoculated seed treatment (29%).