Location: Soybean Genomics & Improvement Laboratory
2021 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
Progress was made to back up Rhizobium trifoli accessions 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 assessed the needs of the agri-business and research community, defined gaps in the Collection and acquired new rhizobium accessions. The effort continues to prepare cultures for long long-term storage at the USDA-ARS National Center for Genetic Resources Preservation in Fort Collins, Colorado. A total of 354 strains have been sent to Fort Collins, Colorado, for preservation. This ensures these agronomically important and irreplaceable resources will always be available for the benefit of U.S. agriculture.
All stakeholder requests for inoculant production for the current growing season were filled even during the reduced access to campus due to the Maximized Teleworking of FY2021. A total of 438 rhizobium cultures were provided to 39 research institutions, non-profit organizations, state and private universities. Rhizobium cultures and technological support were also provided to a number of U.S. commercial enterprises specializing in the production of rhizobium inoculants for legume crops, including Bio-Next (Wichita, Kansas), Biozyme Inc. (St. Joseph, Missouri), Corteva Agriscience (Indianapolis, Indiana), Everyday Minerals, Versailles, Kentucky, Grassland Oregon, Inc. Salem, Oregon, Terramax, Inc. (Bloomington, Minnesota) and Visjon Biologics (Wichita Falls, Texas). The Collection continues its collaboration with the University of Virginia, a historic African American University, to develop a winter hardy faba bean by providing 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 the U.S. soybean belt and determine efficiency on 8 soybean lines. Soil samples were obtained from soybean production fields in Warnock, Calhoun, Bosket Counties in Arkansas, Bosket Counties in Arkansas, and Boone, Dekalb, and Perry Counties in Missouri. Isolation of strains and test of their nitrogen fixation efficiency are in progress.
The Collection has selected and helped to activate and grow approximately 250 Bradyrhizobium and other strains for the DNA isolation and whole-genome sequencing. The sequence information will facilitate the characterization of genetic diversity of the USDA Rhizobium Germplasm Collection.
The Collection updated the online database. Data that only existed as hard copy notes have been added to describe better and define accessions. Information concerning the geographical origin, greenhouse test results, the names of those who had contributed the strains, and comments from previous curators was incorporated into the searchable database.
Accomplishments
1. Resource for biological nitrogen fixation research and inoculant production. Rhizobia can provide all the nitrogen a legume crop needs through biological nitrogen fixation, but not all rhizobia have this ability. Frequently, researchers and inoculant producers do not possess the best rhizobia cultures for their legume crops. The USDA-ARS Rhizobium Germplasm Collection assesses the nitrogen-fixing ability of rhizobia in the Collection and has the expertise to make recommendations for the best choice of rhizobia for inoculant production. This year, the Collection provided recommendations for Rhizobia inoculant and supplied over 438 cultures and strain information to 39 institutes, universities, government agencies, and seven private companies. Researchers, producers, and farmers used the strains and the information to investigate biological nitrogen fixation, produce pure inoculants for crop application, register the inoculants for use in the United States and for export abroad, and preserve these cultures for use long term preservation.
