THE ROLE OF HOST-PATHOGEN-ENVIRONMENT INTERACTIONS IN SUCCESSFUL BIOLOGICAL CONTROL OF CIRSIUM ARVENSE WITH THE RUST FUNGUS PUCCINIA PUNCTIFORMIS
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Open Access
- Author:
- Conaway, Steven Andrew
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 25, 2016
- Committee Members:
- Scott Alan Isard, Dissertation Advisor/Co-Advisor
Scott Alan Isard, Committee Chair/Co-Chair
Donald Durwood Davis, Committee Member
Katriona Shea, Committee Member
David A Mortensen, Outside Member
Gary W Moorman, Committee Member - Keywords:
- biological control
invasive weeds
canada thistle
rust fungus
cirsium arvense
puccinia puntiformis - Abstract:
- The noxious weed Canada thistle, Cirsium arvense, causes extensive problems in agricultural and conservation land worldwide. Systemic infections of the host-specific rust pathogen Puccinia punctiformis produce severe impacts on C. arvense survival and the pathogen has been explored as a potential biological control agent since 1893. Implementing successful biological control has been limited by ineffective inoculation methods, low disease incidence within weed patches, inconsistent disease latency, and lack of spread across the landscape. Overcoming these hurdles requires knowledge of P. punctiformis epidemiology, specifically the interplay of host-pathogen-environment, in producing severe and widespread disease. Experiments were conducted to determine the infection court and seasonal timing required for systemic P. punctiformis disease. Statewide Pennsylvania field trials were conducted to test a novel technique utilizing living, diseased C. arvense transplants as an inoculum source. Late season root inoculations with teliospores were found to be most effective at producing systemic disease. Transplanting diseased plants did not produce significant infections compared to control patches. The role of C. arvense landscape distribution, genetic diversity, and host resistance in limiting biological control efficacy was investigated by testing natural C. arvense populations from three sites in Pennsylvania. Landscape surveys of C. arvense density showed aggregated weed distributions, but with high connectivity between patches. Host diversity within and between patches was determined with SSR markers and unique genotypes were clonally propagated and challenged with inoculations. Highly variable host resistance was observed within patches of C. arvense. Pathogen movement and spread was investigated with a series of experiments to evaluate production and dispersal characteristics of the two infective P. punctiformis spore types. Aerial spore concentrations were measured with volumetric spore traps in naturally infected C. arvense patches. Dispersal gradients were measured by releasing spores in windy field conditions and capturing spores at different distances from the source. Timing and quantity of spores released were evaluated in systemically infected thistle patches. Terminal velocities of spores were also compared in a particle settling tower. By all measures, aerial movement is significantly different between the two major spore types but both are capable of escape from weed patch canopies and landscape scale dispersal given the right meteorological conditions. Better understanding of infection conditions, pathogen dispersal and host resistance helps progression towards prescriptive applications of P. punctiformis for effective biological control but the litany of natural limitations delimited by this research explains why success with this pathosystem has remained elusive for so long.