Simple artificial infection method of Cirsium arvense (L.) Scop. with the obligate pathogen Puccinia punctiformis and regrowth from  root. 

Søren Sørensen
Hedmark college Research Unit, Dept. Agricultural and Natural Science, Hedmark college, Norway
Soren.Sorensen[at]lnb.himh.no

Cirsium arvense, Creeping or Canada thistle is an increasing problem for farmers. Several attempts to use biological control have been studied. As pathogen to C.arvense. Rostrup1 (1873) noticed the increased number of infected plants by Puccinia punctiformis with increased density of the weed and in 1923 this pathogen was tested in laboratory and in fields. Berestetskii (1997) surveyed the fungal ecology of C.arvense and found 70 different pathogens in 150 specimens. Some have been tried as an agent for mycoherbicide on  C.arvense 2,3,4,5,6.  In contrary to other pathogens P. punctiformis is an obligate parasite to C.arvense. The pathogen is ubiquitous, easy to distinguish and to extract. 

In spring, 2002, we transplanted 120, apparently healthy, plantlets of C.arvense at 8-10 leaf stadium were in tubes, containing surface soil, with 10 plants in each tube. The dimension of the tubes was150 cm long, Ø 40 cm.
In late June, P.punctisformis infected thistle were collected outside the trial area. About 50 leaves were swilled in 1 l of water for 1 hour, with a drop of detergent. The suspended spores were harvested by sieving and centrifugation at 7000 rpm for 10 min and applied to the test  plants in 9 tubes by household atomizer. The application was repeated once in mid-July. In August, all treated plants had developed uredosori. All adventitious shoots were heavily infected by the pathogen and died off before end of season. In October, the roots were harvested and stored at 3°C for 6 weeks. 25-30 cm pieces of roots, from the superficial part, were laid out in buckets in sterilized soil. The buckets where kept moist at 10-12°C in 16 hour light. In February, the plants and roots in the buckets were harvested. Green shoots and emerging shoots, the number of healthy or infected shoots, numbers of shoot buds, healthy or diseased, and degree of root infection, was assessed. 

Shoots emerging in buckets showed both pycnium and uredium to a various degree. The two forms appeared on shoot from the same root piece. This suggest that the fungus can become systemic after a secondary infection. Roots from P.punctisformis infected plants exhibited increased sprouting compared to roots from non-infected plants. Increasing infection in root increased also senescence of shoots and shoot bud. 

The increased sprouting in roots from infected plants will consume energy resources, thus weakening the ability of the plant to generate new shoots. The increased sprouting and senescence of buds in diseased root can be utilized in a weed strategy to decrease C.arvense population in combination with fallow in agricultural fields.

References 
1.	 Rostrup 1873 in Ferdinansen 1923
2.	Ferdinansen C. 1923 Nordisk Jordbrugsundersøgelser pp. 475-487
3.	Green S., Mortensen K., Bailey K.L. 2001 Biol.Cont.vol.20 pp. 57-64
4.	Guske S., Boyle C., Schulz B. 1994 2nd Int.conf.on hamful and benef.microorg. in Grassl. Pastures and Turf. Eds Krohn K., Volker H.P. pp. 281-290
5.	Hurrell G.A., Bourdot G.W., Saville D.J. 2001 Biocont.Sci.Tech. Vol.11 pp.317-330
6.	Vurro M., Bottalico A., Zonno M.C. Inform.Fitopatol.vol.43.pp.53-55