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ARS Home Midwest Area St. Paul, Minnesota Plant Science Research Research





- Samac, Deborah - Debby
- Soil and Air (212)
- Grass, Forage, and Rangeland Agroecosystems (215)
- Plant Genetic Resources, Genomics and Genetic Improvement (301)

Research Project: **Location:
                            Plant Science Research** Project Number: 5062-21500-001-006-S
                        
                        Project Type: Non-Assistance Cooperative Agreement Start Date: Jun 1, 2020
                        
                        End Date: May 31, 2025 **Objective:**
                        
                        Objective 1: Develop recommendations on optimum harvest schedules for new alfalfa varieties based on economic return.
Objective 2: Identify potential positive associative effects between alfalfa and corn silage on improving the amount and efficiency of milk protein and milk fat yield in high producing cows.
Objective 3: Determine the relationship of alfalfa plant population densities and stem density with forage yield of modern alfalfa varieties with fall dormancy ratings 4 and 5 over a range of alfalfa stand ages.
Objective 4: Test efficacy of fungicides when used as seed treatments for control of seed rot and damping off of alfalfa under field conditions.
Objective 5: Identify the entire microbial communities (bacteria, fungi, oomycetes and nematodes) associated with infected alfalfa seedlings and soil samples from sites with poor alfalfa establishment.
Objective 6: Quantify the abundance of known seed rot and seedling root rot pathogens sites with poor alfalfa establishment. **Approach:**
                        
                        For Objective 1, plots with 10 alfalfa cultivars ranging in fall dormancy will be harvested at 21-, 28-, and 35-day intervals. Forage yield and quality will be measured at each harvest. Stand establishment and persistence will be determined by counting stems 4 weeks following seeding, in the fall of the seeding year, and in the spring of the following years. Data will be used to calculate relative feed value, relative forage quality, milk Mg ha ̄1 and net economic return. 

For Objective 2, following a 2-wk covariate period, cows will receive a treatment diet for 4 weeks. Diets will consist of five ratios of chopped alfalfa hay-to-corn silage: 90:10, 70:30, 50:50, 30:70, and 10:90. Animal measurements will include: dry matter intake, milk yield and composition, feed efficiency, and body weight and body condition score. 

For Objective 3, two varieties at fall dormancy 4 or 5 at seven densities will be used to determine stem counts and forage yields. Data will also be collected from production hay fields planted to alfalfa varieties with fall dormancy 4 or greater. Ten sampling sites each of 3 ft -square area will be selected for stem counts, plant count and yield determination. Agronomically optimum plant population and stem density will be determined based on the relationship between yield and plant populations and stem density. 

For Objective 4, commercially available fungicides will be tested for efficacy under field conditions at five locations. Plant counts will be done approximately 10 days after planting (dap), 30 dap, and 60 dap. Forage yields will be measured, plants rated for disease symptoms, and plant dry weight measured. 

For Objective 5, seedlings and soil will be sampled from control plots used for Objective 4. Approximately 20 seedlings and surrounding soil will be removed from the plots. DNA will be extracted from plant and soil samples then submitted for amplicon sequencing to identify bacteria, fungi, oomycetes, and nematodes to identify the organisms causing seedling diseases in soils with poor seedling establishment. 

For Objective 6, we will use the DNA extracted from roots and soil for Objective 5 in quantitative PCR assays to measure the abundance of Phytophthora medicaginis, Aphanomyces euteiches, Pythium irregulare, P. sylvaticum, and P. ultimum. In 2021, we will index soils using the quantitative PCR assays from sites in Wisconsin, Minnesota, South Dakota and request soils from other locations with poor alfalfa stand establishment. Soils will also be used in bioassays to determine the race of Aphanomyces euteiches present. These experiments will help identify which pathogen(s) is most prevalent in soils and diseased alfalfa roots and therefore likely causing the most damage.


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