Biological Control Research

My PhD research at Penn State is focused on the biological control of the invasive weed Canada thistle (Cirsium arvense). The rust fungus Puccinia punctiformis systemically infects Canada thistle, killing diseased shoots.  The pathogen has been investigated as a biocontrol agent in the past, but has been limited by low disease intensity within thistle patches.  I have taken an integrated approach to this problem by focusing on the many factors involved in biological control.  I am investigating the potential genetic resistance of Canada thistle to different strains of the pathogen; the exact conditions needed for the pathogen to successfully infect; and the pathogen's ability to move throughout the landscape. This research has involved many different techniques including greenhouse propagation, molecular genotyping, GIS mapping, field data collection, and many lab methods.



The wind-blown seeds of Canada thistle (L) a Canada thistle shoot systemically infected with P. punctiformis (R)

Canada thistle has multiple infection strategies, producing localized lesions on leaves from urediniospores and systemic infection through basidiospores.  Systemic disease leads to higher mortality, so biological control is often focused on the introduction of basidiospores (via teliospores) to healthy plants. Thistle rust is an obligate biotroph, meaning that it needs a living host to complete its lifecycle.  It cannot be grown in culture, so delivering the pathogen to healthy patches requires utilizing living plants.



basidiospores (blue) germinating from teliospores (brown) of P. punctiformis