Description

A poster presented at the 2012 Global Pulse Researchers Meeting, Kigali, Rwanda- “Transforming Grain-Legume Systems to Enhance Nutrition and Livelihoods”. Abstract: Common beans are reported to have the lowest percent N2 derived from N fixation among legumes. Although germplasm with superior BNF has been identified, the genetic and physiological bases for greater capacity for nitrogen assimilation is not established. The objectives of this study is to identify phenotypic traits associated with improved host-rhizobia interactions and N2 fixation. Greenhouse studies were undertaken to determine indigenous rhizobia levels all US and HC sites, characterize soil rhizobia soil populations and strain diversity sites, and bait soil rhizobia populations and analyze nodule DNA for indigenous strains. Preliminary analyses of indigenous levels of rhizobia using diluted soil extracts indicated very low levels of infection/nodulation at some HC sites. Fifty-one lines have been screened for BNF using 15N dilution. The proportion of total plant N supplied by N fixation varied from 49% 77%. Analysis of trial inoculants indicated low titer of rhizobia in some cases, and presence of enterobacteria in inoculant used in Rwanda. This result could explain variation in inoculation response observed in related field trials. Grafting studies between common bean lines and between common bean and soybean lines were conducted to assess root/shoot limitations for nodule formation and BNF. Initial results indicate both root and shoot factors control nodulation, and considerable potential exists to enhance nodule formation and effectiveness by manipulating root/shoot communication.