Improving Alfalfa Seedling Establishment: Understanding and Managing the Components of Wet Soil Syndrome
2022-05
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Improving Alfalfa Seedling Establishment: Understanding and Managing the Components of Wet Soil Syndrome
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2022-05
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Alfalfa stand health and persistence is dependent on rapid and uniform seedling emergence. Pathogens such as Aphanomyces euteiches, Phytophthora medicaginis, Pythium spp., Fusarium spp., and Rhizoctonia solani plague alfalfa seedlings leading to decreased stand health and an overall decrease in yield over an alfalfa stand’s life. The objectives of this study were to test the efficacy of fungicides when used as seed treatments for control of seed rot and damping-off of alfalfa under field conditions, identify the microbial communities (bacteria, fungi, and oomycetes) associated with infected alfalfa seedlings and soil samples from sites with poor alfalfa establishment, and quantify the abundance of known seed rot and seedling root rot pathogens from sites with poor alfalfa establishment. Field trials were conducted in Wisconsin in 2020 and 2021 in fields with previous alfalfa stand establishment issues to test the efficacy of the five different fungicide seed treatments. Rhizosphere soil, bulk soil, and root samples were taken from each field trial site and DNA was extracted from the samples. The DNA samples were submitted to the University of Minnesota Genomics Center (UMGC) to identify the entire microbial community of the sites. qPCR assays were conducted using the rhizosphere soil and root DNA samples to identify the abundance of the pathogens present. Results from the field trial indicated seed treatments may aid in stand establishment and an increase in yield. Results from growth chamber assays indicated fungicide seed treatments do aid in protecting alfalfa from Pythium spp. and Phytophthora medicaginis but did not add any control to Aphanomyces euteiches. Seed treatments also added control in field soils when tested under controlled environments and results indicated that experimental fungicides not currently labelled for alfalfa offered more control as compared to fungicides currently used on alfalfa today. Oomycete sequencing revealed A. euteiches was the dominating pathogen at the plot locations in Wisconsin followed by P. medicaginis. Pythium diversity was high in the rhizosphere. Phytophthora sansomeana was identified in relatively high abundance. This pathogen could be contributing to seed rot and damping-off in alfalfa seedlings and may have gone previously unrecognized as contributing to wet soil syndrome in alfalfa. Fungal sequencing revealed pressure from potentially unrecognized pathogens, Paraphoma radicina and Plectosphaerella cucumerina. qPCR results confirmed high A. euteiches quantities at all plot locations and higher A. euteiches pressure in the race 2 susceptible cultivar, Ameristand, as compared to the race 2 resistant cultivar, MegaTron AA. P. medicaginis and Pythium spp. quantities were lower than A. euteiches, which is consistent with sequencing relative abundance results. Sequencing of the microbial community identified pathogens that could be contributing to alfalfa seedling diseases and qPCR assays allowed for quantification of known pathogens. Results from this study will inform future alfalfa breeding efforts to ultimately lead to increase profitability for alfalfa producers that are plagued with alfalfa establishment failure due to wet soil syndrome.
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University of Minnesota M.S. thesis. May 2022. Major: Applied Plant Sciences. Advisors: Deborah Samac, Craig Sheaffer. 1 computer file (PDF); vi, 148 pages.
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Larsen, Leta. (2022). Improving Alfalfa Seedling Establishment: Understanding and Managing the Components of Wet Soil Syndrome. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/241256.
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