Graduate Thesis Or Dissertation
 

Scratching the Surface of the Potato Geocaulosphere: Characterizing the Microbiome of Seed Tuber Tare Soil and its Impact on the Rhizosphere Microbiome

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rn301798c

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  • For tuberizing crops like potato (Solanum tuberosum), the geocaulosphere, or the zone of soil in contact with and influenced by the tuber, is a distinct sphere of microbial life and represents an important interface between the potato crop and the soil environment. Upon potato harvest, specific geocaulosphere soil called tare soil remains adhering to the tuber surface. Because potato is a vegetatively propagated crop, relying on the production of seed tubers in limited generations, seed tubers are transported along with their respective tare soils from seed grower farms to potato farms for fresh market production. Although tare soil is recognized as a potential avenue of pathogen inoculum to agricultural soils, little is known about tare soil associated microbes or how microbial communities on the tuber surface may vary in composition. Variability in the tare soil microbiome may influence the development of the potato microbiome as the plant grows from the seed piece. For example, microbes in tare soils may serve as a primary inoculum source for the rhizosphere, which is quickly colonized by microbes as the root system develops. Here we seek to characterize and explore the microbial communities of tare soil and ask whether they influence the potato rhizosphere microbiome. In Chapter 2, we characterized the bacterial and fungal tare soil microbiome of potato using ITS and 16S metabarcoding and identified factors important for describing variation among microbial communities. Tare soils were opportunistically collected from import seed lot trials, which included seed lot submissions from a range of seed grower sources and potato varieties. We identified a core microbiome of 61 bacterial and 26 fungal taxa, many of which had not been previously associated with potato or potato agricultural soils, have been recognized as plant growth promoters and biological control agents, or are putative potato pathogens. Finally, we examined factors influencing the tare soil microbiome and found that seed grower source explained a significant amount of variation in microbial communities. Our results also support evidence of a geospatial pattern by which tare soils grown at seed farms that were closer together geographically were also more similar in microbial community composition. In Chapter 3, we sought to explore whether microbial communities in tare soil influence the rhizosphere microbiome, which is widely recognized as an important microbial habitat contributing to plant health. We characterized the fungal and bacterial rhizosphere microbial communities of potato plants grown in a greenhouse experiment. We hypothesized that tare soil would influence rhizosphere community composition and tested this hypothesis in both an agricultural and non-agricultural soil, situating the tare soil effect within the context of an ecologically and agriculturally important known influence on the rhizosphere microbiome. To measure the effect of tare soil on rhizosphere communities, seed tubers either received a surface sterilization treatment prior to planting or were planted with their tare soil intact as a control. We found that tare soil did influence microbial communities in the rhizosphere, but more strongly for fungi than bacteria. However, this effect overall was small compared to the influence of microbial communities in the bulk soil. Overall, our findings highlight the geocaulosphere as an underrated microenvironment for potato plants with potentially significant implications for plant health. The tare soil microbiome hosts variable communities of fungi and bacteria, and we demonstrated that these communities can be important for developing microbial communities of the potato plant. This work offers a comprehensive look at the tare soil microbiome and sets the stage for future work seeking to address the functional consequences of these communities for potato health and productivity.
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  • Pending Publication
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  • 2021-03-17 to 2023-04-18

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