Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Biological Science (MBioSci)

Department

Plant, Soil, and Environmental Sciences

First Committee Advisor

Jianjun (Jay) Hao

Second Committee Member

Robert P. Larkin

Third Committee Member

Bee Chim

Abstract

Verticillium wilt of potato caused by Verticillium dahliae is among the most economically impactful in potato production, resulting in as much as a 50% reduction in potato yield. Chemical fumigation with metam sodium has been commonly used for controlling this pathogen. The impacts of repeated and successive treatments of fumigation on soil microbial communities are still being explored. Furthermore, decreased efficacy of metam sodium after repeated or successive applications on the same soil have been reported. The goals of this project were to determine the efficacy of three fumigation-rotation plans in treating Verticillium wilt of potato, to explore the impacts of fumigation-rotation on soil microbial community diversity, and to identify candidate microbes for the xenobiotic degradation of metam sodium in repeatedly fumigated soils. A three-year field trial was conducted in Presque Isle, Maine starting in September 2021 and ending in August 2024. Three fumigation-rotation treatment groups and a non-fumigated control were established: Once-fumigated, twice-fumigated, and thrice-fumigated. V. dahliae inoculum was broadcast spread in the field every fall before fumigation. Additionally, during the second year of the trial (2023) half of the field was planted with Golden mustard (Brassica juncea) with the goal to induce further abundance of microbes capable of metam sodium degradation. Tubers were harvested, weighed, and evaluated for Verticillium wilt incidence and disease severity every fall, and soil samples were collected at three points each growing season for bacterial and fungal DNA sequencing. Despite inoculating the field with V. dahliae each fall, disease presence was minimal all three years, and there was no significant impact of fumigation or fumigation-rotation on Verticillium wilt disease or tuber yield during this experiment. Soil microbial alpha and beta diversity were significantly impacted by metam sodium fumigation, bacteria more so than fungi. Additionally, there was evidence of decreased efficacy of metam sodium after a third, successive application in both disease and yield response data and in impact to soil microbial diversity. In year three, high incidence of scab diseases occurred so disease data were collected. Mustard rotation and biofumigation impacted soil microbial community and scab disease incidence and severity more in the final year of the project than was expected, and biofumigated soil had significantly less scab severity than potato-monocropped soil and produced marginally higher yields. In the final year of the study, microbial diversity was higher in non-fumigated plots compared to fumigated plots, but including mustard-potato-rotation to fumigated soil reduced these effects and improved microbial diversity. Metam sodium and mustard applications significantly altered microbial abundance. Differential abundance analysis identified candidate microbes for metam sodium degradation: two Pseudomonas sp., one Pseudarthrobacter sp. and two Massilia sp. Further research is suggested to confirm these degradative capabilities.

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