Location: Soybean Genomics & Improvement Laboratory
2020 Annual Report
Objectives
Objective 1: Manage the USDA-ARS National Rhizobium Germplasm Resource Collection in Beltsville, Maryland, by preserving and curating germplasm, defining gaps in the collection, acquiring new accessions, distributing isolates to customers and stakeholders and updating a public, electronic database of the collection that is easily accessible to all users. [NP301, C2, PS2A]
Objective 2: Isolate and characterize Bradyrhizobium strains from major soybean growing regions in the United States to produce region-specific soybean inoculants for greater nitrogen fixation efficiency in commercial soybean production. [NP301, C1, PS1A]
Approach
For Objective 1, rhizobial cultures will be managed by their preservation, quality control and disbursement to ARS customers upon request. Technical information about rhizobia, their isolation, culturing and symbiosis and advice will be given. New rhizobial cultures will be isolated from soil samples. Emphasis will be placed on preparing and sending cultures for long-term backup at the USDA, ARS, National Center for Genetic Resources Preservation, Fort Collins, CO. For Objective 2, soil samples will be taken from prime farmland from areas of soybean production in the Midwest. Three counties from each of the top ten states (IL, IA, MN, IN, NE, OH, MO, SD, AR, and ND) with the highest recorded production of soybean will be selected for sampling. The soil will be collected from different soil series. Isolation of rhizobia will be performed using ‘Lee’ as a capture host. Rhizobia living in the rhizosphere will be recovered on selective media. If the sequence of the isolate is unique, the isolated rhizobia will be grown in liquid culture and used as inoculant on 8 milestone soybean cultivars: ‘Adams’, ‘Forrest’, ‘Harosoy’, ‘Hutcheson’, ‘Kent’, ‘Lee’, ‘Mercury’ and ‘Williams 82’, which capture 75% of the genetic diversity of 562 North American commercial cultivars in the USDA-ARS Soybean Germplasm Collection. Nitrogen fixation efficiency will be determined by measuring the chlorophyll content of soybean leaves. Bradyrhizobium spp. that meet or exceed nitrogen fixation efficiencies of controls on any of eight milestone cultivars will be used in subsequent field experiments. The seed yield and protein content of three widely-used commercial cultivars inoculated with and without each strain and inoculated with the most commonly used strain control (USDA 110) will be compared. Desirable strains should provide similar or superior yield and protein content compared to the control.
Progress Report
The two milestones of Objective 1a are to back up 527 accessions of Sinorhizobium meliloti and Rhizobium trifoli from the Rhizobium Collection to the long-term storage facility at Fort Collins and to fulfill the requests of all stakeholders of the USDA-ARS Rhizobium Germplasm Resource Collection in a timely manner. The collection is curated by assessing the needs of the agri-business and research community, to define gaps in the collection and to acquire new rhizobium accessions to meet these needs. Preserving the collection is of the utmost importance. The effort continues in the preparation of cultures for long-term storage at the USDA-ARS National Center for Genetic Resources Preservation in Fort Collins, Colorado. This action ensures these agronomically important and irreplaceable resources will always be available for the benefit of U.S. agriculture. This year, 490 strains have been sent to Fort Collins for long-term preservation. We timely provided rhizobium cultures and technological support to businesses and to non-profit organizations specializing in the production of rhizobium inoculants for legume crops as soon as we received the requests. This year the Collection provided more than 200 cultures to meet the needs of scientists at universities and governmental agencies and customers who produce rhizobium mixtures for crop application. Five of the commercial enterprises assisted by the collection are U.S.-owned businesses. These are Bio-Next (Wichita, KS), Biozyme Inc. (St. Joseph, MO), Corteva Agriscience (Indianapolis, IN), Terramax, Inc. (Bloomington, MN) and Visjon Biologics (Wichita Falls, TX). We also provided rhizobial cultures and technical assistance to support 1890 Institutions and other state and private universities. The USDA Rhizobium Collection is providing support in a collaboration with the University of Virginia to develop a winter hardy faba bean. Project staff spent many hours consulting stakeholders by telephone and email and dispensed advice on recommended strains for each legume, protocols on media preparation, and optimal culture growth conditions.
The milestone of objective 1b is to capture Bradyrhizobium on soybean cultivar Lee from soil samples taken from geographical regions in the U.S. soybean belt, and to determine efficiency on 8 soybean lines. Soil samples were obtained from soybean production fields in Knox, Montgomery and Trumbull Counties in Ohio, and from Morgan, Noble and Spencer Counties in Indiana. Some isolates were identified by DNA sequencing as being Bradyrhizobium japonicum and will be evaluated for efficiency in nitrogen fixation on soybean.
Accomplishments
1. New isolates of nitrogen-fixing bacteria for soybeans. USDA-ARS in Beltsville, Maryland, is home to the U.S. rhizobium collection. Rhizobia are bacteria that form root nodules on legumes like soybeans, and they allow them to grow naturally without added topical fertilizer. Seeking to add new rhizobium strains to the collection, USDA-ARS scientists in Beltsville, Maryland, collected soils from different areas of the U.S. where soybeans are grown. The scientists identified six isolates of Bradyrhizobium japonicum, the species that fixes nitrogen for soybeans. A DNA test confirmed that these isolates were not in the collection. All six isolates demonstrated the ability to nodulate and fix nitrogen on eight different varieties of soybean. If the isolates are proven to be superior nitrogen fixers, the collection will distribute them to soybean farmers to help improve U.S. soybean production.
