Evaluation of two Sustainable Practices for Plant Pathogen Eradication
Open Access
- Author:
- Harvey, Robert Jonathon
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 27, 2018
- Committee Members:
- John Andrew Pecchia, Dissertation Advisor/Co-Advisor
John Andrew Pecchia, Committee Chair/Co-Chair
David Michael Geiser, Committee Member
Maryann Victoria Bruns, Committee Member
Rachel Alice Brennan, Outside Member
Donald Durwood Davis, Dissertation Advisor/Co-Advisor - Keywords:
- boxwood blight
plant pathology
Calonectria
mycology
constructed wetlands
composting
compost
eradication
ammonia - Abstract:
- Boxwood blight is a disease impacting much of the United States, at least 26 states as of the time of this writing. Caused by the pathogens Calonectria pseudonaviculata and C. henricotiae, the disease is found worldwide. Currently, only C. pseudonaviculata is found in the United States, while both species are found in Europe. Like other species in the genus, both C. pseudonaviculata and C. henricotiae are prolific microsclerotia producers. Due to the resistant nature of these survival structures, extended survival under extreme environmental conditions is possible, which could then lead to subsequent dissemination of the pathogen. During the past 10-20 years, much attention has been given to diverting organic matter from our landfills, with composting often being the proposed method for the disposal of organic matter. However, if infected plant material containing microsclerotia are present in the organic waste stream, it is possible that the pathogen could survive the composting process, therefore the use of finished compost could inadvertently serve as a vector for the pathogen. Another area of concern potentially leading to the spread of the pathogen is through water runoff from nurseries. This wastewater can also be high in nutrients, like nitrate and ammonium, spurring eutrophication processes in bodies of water in which they discharge. Capturing and reusing this wastewater can help reduce fertilizer costs, and prevent pollution, however it may also lead to pathogen levels building up due to water recirculation in these systems. Treatment solutions like constructed wetlands could possibly serve to mitigate this problem. To address these challenges, two systems were constructed, one consisting of nine composting bioreactors, and one consisting of nine constructed wetlands. To evaluate compost survival, microsclerotia of C. pseudonaviculata were grown on cellophane and inoculated into compost. Survival was compared at 24, 48, and 72 h at temperatures of 40, 50, and . Based on the results of these experiments, it was conclusively demonstrated that microsclerotia survival in compost ≥ for 24 h or longer is not expected. Survival in compost was less than that of heat alone, leading to an experiment evaluating the impacts of ammonia. Both species of Calonectria were evaluated for ammonia sensitivity at the USDA BSL-3 facility housed at Ft. Detrick (Frederick, MD). Based on these results no significant differences in ammonia sensitivity between the two species were observed. Exposing the C. pseudonaviculata microsclerotia to gaseous ammonia at for 24 h reduced survival rates compared to heat alone, but still not as efficient as compost. Similar work was done to evaluate C. pseudonaviculata survival in a wetland, with a few key differences. Due to the regulatory nature of C. pseudonaviculata research, Verticillium dahliae was used as a proxy. Microsclerotia were grown on cellophane and inoculated into the wetlands. Nine wetlands were constructed using one of three different substrates: unplanted gravel, planted gravel, and planted gravel/spent mushroom compost mix, with three cells per treatment. None of the three treatments caused complete eradication of the microsclerotia through 7 days. This indicates that while constructed wetlands could serve as a filter reducing the number of pathogens in the irrigation water system, survival of the pathogens can be expected, leading to future reintroduction. While not ideal for plant pathogen eradication, both planted treatments showed promise in nitrate removal. All findings and results discussed do not necessarily reflect the views of any of the funding agencies.