Asymptomatic systemic disease of Canada thistle (Cirsium arvense) caused by Puccinia punctiformis and changes in shoot density following inoculation

• Published in: Biological control Vol. 86; pp. 28 - 35
• Main Authors: Berner, D.K., Smallwood, E.L., Cavin, C.A., McMahon, M.B., Thomas, K.M., Luster, D.G., Lagopodi, A.L., Kashefi, J.N., Mukhina, Zhanna, Kolomiets, Tamara, Pankratova, Lyubov
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-07-2015
• Subjects: Biological control; Canada thistle; Chemiluminescence western slot blot; Cirsium arvense; Epidemics; Rust fungus; Systemic disease; Rust fungus; Epidemics; Biological control; Canada thistle; Systemic disease; Chemiluminescence western slot blot; Cirsium arvense
• ISSN: 1049-9644; 1090-2112
• DOI: 10.1016/j.biocontrol.2015.02.006

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•P. punctiformis was found in 50–60% of roots from asymptomatic C. arvense plants.•C. arvense shoot densities declined in all 10 sites after inoculation.•C. arvense shoot density reduction after inoculation averaged 73% by 54months.
Canada thistle (Cirsium arvense) is one of the worst weeds in temperate areas of the world. A rust fungus, Puccinia punctiformis, was first proposed as a biological control agent for C. arvense in 1893. The rust causes systemic disease which ultimately kills C. arvense plants. In 2013 it was demonstrated in four countries, that inoculation of C. arvense rosettes in the fall with ground telia-bearing leaves can initiate epidemics of systemic rust disease with an average of 28% of inoculated rosettes producing a systemically diseased shoot the following spring. Other rosettes that emerged near inoculation points in spring were stunted and appeared diseased. To determine whether other rosettes were diseased, a chemiluminescence western slot blot test, applying polyclonal antibodies raised against P. punctiformis antigens, was developed to detect the fungus in roots. Rosettes were inoculated with telia-bearing leaves in the fall in Maryland, USA and Veroia, Greece. Roots of asymptomatic rosettes that emerged adjacent to inoculation points the following spring were tested for the presence of the fungus with the slot blot test. Rosettes that had diseased shoots were recorded. Based on the slot blot tests, 50–60% of the asymptomatic rosettes adjacent to inoculation points were positive for presence of the rust and likely to be systemically diseased. To demonstrate that systemic disease leads to C. arvense decline, C. arvense shoot densities were measured annually at 10 sites, in three countries, that had been inoculated with telia-bearing leaves in the fall between 2008 and 2012. Changes in C. arvense shoot densities over time were calculated. Average reductions in C. arvense density across the 10 sites were 43.1±10.0% at 18 months after inoculation, 63.8±8.0% at 30months after inoculation, and 80.9±16.5% at 42months after inoculation, and 72.9±27.2% at 54months after inoculation; the 54month reduction was, however, based on only two sites.