Project Number: 8042-21000-285-000-D
Project Type: In-House Appropriated
Start Date: May 9, 2018
End Date: May 8, 2023
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]
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.