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

Some dynamics of spread and infection by aeciospores of Puccinia punctiformis, a biological control pathogen of Cirsium arvense

“…The distance of effective dispersal from the source area to shoots bearing leaves with uredinia and or telia was less than 17 m (Fig. 2), and this short-distance spread partially explains why systemic disease of CT caused by P. punctiformis is not wide-spread; the initiating spores (aeciospores) for epidemics are not dispersed long distances and neither are telia-bearing leaves that result from aeciospore infections (Berner et al, , 2015. Although these results are from one location only, and higher wind speeds in other locations might result in longer absolute dispersal distances, increased absolute dispersal distances may not increase effective dispersal distances, i.e., distances aeciospores are dispersed and result in infections that produce uredinia.…”

“…Artificially initiating epidemics of systemic disease by applying ground telia-bearing leaves, collected in mid-to late-summer, to newly emerging CT rosettes in the fall ) is a simple approach to establish effective biological control of CT (Berner et al, 2015). This can be done anywhere the rust is found on CT, which is virtually every state and country where CT is found (Farr and Rossman, 2015).…”

“…Thus, the probability of successful systemic infection resulting from one-to-several telia is low, and the dispersal distance to establish adequate numbers of telia for successful basidiospore infections is probably much less than effective aeciospore dispersal distance measured by the presence of one-to-several uredinia/telia. Once telia are formed in leaves and the leaves abscise in the fall, the dispersal of these leaves is also short distance (Berner et al, 2015). Thus the fungus is not dispersed far from systemically-diseased aeciospore-producing shoots that emerge in the spring, and establishment of epidemics of systemic disease that are widespread enough for effective biological control will require manipulation by man.…”

“…Aeciospores are voluminous, extremely friable, and readily wind-blown while urediniospores are neither voluminous nor particularly friable. Rather, they are embedded in leaf tissue and gradually transition to diploid telia and teliospores in late summer (Cockayne, 1915;Buller, 1950;Menzies, 1953;Bailiss and Wilson, 1967;Kirk et al, 2001;Berner et al, 2015) (Fig. 1).…”

“…Systemically diseased plants and all of the shoots on infected root systems eventually die (Watson and Keogh, 1980). Gradually, entire systemically diseased CT patches die and disappear (Berner et al, 2015). In 2013, Berner et al clarified the disease cycle of the rust and demonstrated that rust epiphytotics can be easily initiated by inoculation of rosettes in the fall with telia-bearing leaves.…”