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Successful establishment of epiphytotics of Puccinia punctiformis for biological control of Cirsium arvense

Dana Berner, Emily Smallwood, Craig Cavin, Anastasia Lagopodi, Javid Kashefi, Tamara Kolomiets, Lyubov Pankratova, Zhanna Mukhina, Michael Cripps, Graeme Bourdôt
Biological control 2013 v.67 no.3 pp. 350-360
Cirsium arvense, Puccinia, aeciospores, basidiospores, biological control, biological control agents, dew, inoculum, leaf abscission, leaves, phenology, rust diseases, shoots, spore germination, spring, summer, teliospores, temperature, weed control, weeds, Greece, Maryland, New Zealand, Russia
Canada thistle (Cirsium arvense, CT) is one of the worst weeds in temperate areas of the world. The rust fungus Puccinia punctiformis was first proposed as a biological control agent for CT in 1893. The rust causes systemic disease, is specific to CT, and is in all countries where CT is found. Despite a 120-year lapse since biological control with the rust was proposed, establishment of epiphytotics of the rust have previously been unsuccessful due to incomplete understanding of the disease cycle. In this study, newly-emerging rosettes in the fall are proposed as the physical and temporal infection courts for basidiospores, from germinating teliospores, to systemically infect CT and give rise to systemically diseased shoots the following spring. To test this hypothesis, rosettes of CT were inoculated in the fall with either telia-bearing leaves collected in mid-summer or with greenhouse-produced teliospores. Field sites were located near Kozani, Greece, Moscow, Russia, Christchurch, New Zealand, and Ft. Detrick, Maryland, USA. Telia-bearing leaves, which were used as inoculum in 12 of 13 field sites, were collected near each field site from CT shoots in close proximity to systemically diseased CT shoots producing aeciospores in the spring. Aeciospore infections of the leaves of these nearby shoots gave rise to uredinia which turned to telia in mid- to late-summer. Temperature and dew conditions at inoculation in the fall at each site were very favorable for teliospore germination. Rosettes inoculated in the fall were marked with flags, and systemically diseased shoots emerging near these flags the following spring were recorded. In 11 of the sites in these countries, individual rosettes were inoculated 2, 4, 6, or 8 times with telia-bearing leaves. Proportions of rosettes giving rise to systemically diseased shoots, out of the number of rosettes inoculated, were analyzed. Inoculations in all 13 sites produced systemically diseased shoots. A separate study on the phenology of CT showed that the maximum rate of leaf abscission occurred at the time of maximum emergence of new CT rosettes in the fall. This period coincided with an annually occurring period of sustained dew and favorable temperatures for teliospore germination. In nature, abscising telia-bearing leaves likely come into contact with a receptive rosette during favorable conditions for teliospore germination in the fall. This study demonstrates that epiphytotics of systemic rust disease of CT can be routinely established, by mimicking the natural disease cycle.