Location: Foreign Disease-weed Science ResearchTitle: Some dynamics of spread and infection by aeciospores of Puccinia punctiformis, a biological control pathogen of Cirsium arvense Author
|Bruckart, William - Bill|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2015
Publication Date: 5/7/2015
Publication URL: http://handle.nal.usda.gov/10113/61430
Citation: Berner, D.K., Smallwood, E.L., Vanrenterghem, M., Cavin, C.A., Michael, J.L., Shelley, B.A., Kolomiets, T., Pakratova, L., Bruckart, W.L., Mukhina, Z. 2015. Some dynamics of spread and infection by aeciospores of Puccinia punctiformis, a biological control pathogen of Cirsium arvense. Biological Control. 88:18-25. Interpretive Summary: Canada thistle is an invasive perennial weed of agroecologies in the temperate areas of the world. In research conducted at the ARS Foreign Disease Research Unit, Ft. Detrick, MD, researchers from Bordeaux Sciences Agro-INRA, the All-Russia Research Phytopathology Institute, and the All-Russia Research Institute for Biological Means of Plant Protection found that asexual spores of the Canada thistle biological control rust fungus could travel only short distances and did not germinate well. However, infection of Canada thistle by these spores resulted in infections that traveled up the shoots of plants. This type of infection seems to compensate for short distance spread of the spores and poor germination. Ultimately, this type of infection may increase the presence of a spore type that leads to long-term infection of Canada thistle roots, and lead to effective strategies for biological control of this important invasive weed.
Technical Abstract: In this study, effective spread of aeciospores from an area source in a field was fit to an exponential decline model with a predicted maximum distance of spread of 30 m from the area source to observed uredinia on one leaf of one C. arvense shoot. However, the greatest number of shoots bearing leaves with uredinia/telia was observed within 12 m of the area source, and there were no such shoots observed beyond 17 m from the area source. Aeciospore germination under laboratory conditions was inherently low, with a maximum of about 10 percent. Temperatures between 18 C and 25 C were most favorable for germination with maximum germination at 22 C. Temperature and dew point data collected from the Frederick, MD airport indicated that optimum temperatures for aeciospore germination in the spring occurred from about May 18 to June 20. Dew conditions during this period were also favorable for aeciospore germination. A total of 122 lower leaves, 2 per shoot, on 61 C. arvense shoots were individually inoculated in a dew tent in a greenhouse by painting suspensions of aeciospores onto the leaves. Of these inoculated leaves, 47 produced uredinia within an average of 21.2 + 6.9 days after inoculation. Uredinia continued to be produced until 48 days after inoculation. An average of 3.9 + 3.75 percent of the leaf areas produced uredinia. Uredinia were also produced, in the absence of dew, on 17 non-inoculated leaves of 12 shoots. These leaves were up to 4 leaves above leaves on the same shoots that had been individually and separately inoculated. Results of PCR tests for the presence of the fungus in non-inoculated non-diseased leaves, showed that 44 leaves above inoculated leaves on 27 shoots were positive for the presence of the fungus. These leaves were up to 5 leaves above inoculated leaves on the same shoot. Uredinia production and positive PCR results on leaves above inoculated leaves on the same shoot indicated that aeciospore infection was weakly systemic. In other tests in which all leaves of plants were spray-inoculated with aeciospores, uredinia were produced by 10 days after inoculation and converted to telia and sole production of teliospores in about 63 days after inoculation. Given the apparent systemic nature of aeciospore infection, successful aeciospore infections from about May 18 to June 20, at Frederick, MD, would be expected to result in uredinia production in excess of a 1:1 ratio of aeciospore infections to uredinia, and ultimately telia production. In turn, systemic aeciospore infection favors re-establishment of systemic disease by increased density of telia on telia-bearing leaves that lead to systemic infection in the fall.