FIRST REPORT OF SILYBUM MARIANUM AS A HOST OF PUCCINIA PUNCTIFORMIS

Authors: Berner, Dana; Paxson, Larry; Bruckart, William; Luster, Douglas - Doug; McMahon, Michael - Mike; Thomas, Jami

Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: 6/1/2002
Publication Date: 11/1/2002
Citation: BERNER, D.K., PAXSON, L.K., BRUCKART, W.L., LUSTER, D.G., MCMAHON, M.B., MICHAEL, J.L. FIRST REPORT OF SILYBUM MARIANUM AS A HOST OF PUCCINIA PUNCTIFORMIS. PLANT DISEASE. 86:1271. 2002.

Interpretive Summary: The rust fungus, Puccinia punctiformis, is well known as a pathogen of Canada thistle throughout the world. Recently we found the fungus parasitizing milk thistle, another invasive weed, in our quarantine greenhouse. Analysis of DNA from fungal spores that developed on the two hosts showed the organism from each host to be the same. The spores from milk thistle were then applied to healthy milk thistle plants, and the disease developed in these plants as well. In nature, Canada thistle and milk thistle occupy different ecological areas: Canada thistle is found predominately in temperate habitats while milk thistle is found in habitats with a Mediterranean climate. Life cycles of each host are also different: Canada thistle is a perennial that emerges in spring and dies back in winter, while milk thistle is a winter annual that emerges in fall and dies in late spring. Thus, the rust from Canada thistle may rarely encounter susceptible milk thistle plants in the field. However, since fungal spores can be produced routinely, there might be potential to use the rust for biological control of milk thistle. This would depend on understanding rust-milk thistle interactions.

Technical Abstract: The rust fungus, Puccinia punctiformis, is well known as a pathogen of Cirsium arvense throughout the world. Recently we found the fungus parasitizing Silybum marianum in our quarantine greenhouse. Analysis of ribosomal internal transcribed spacer sequences from fungal spore DNA isolated from the two hosts showed the organism to be the same. As the fungus infection developed on S. marianum, uredinia and urediniospores were produced. Urediniospores from infected leaves were harvested and sprayed onto young S. marianum plants grown in isolation from P. punctiformis. These plants also became infected and produced urediniospores. In nature, C. arvense and S. marianum occupy different ecological areas: C. arvense is found predominately in temperate habitats while S. marianum is found in habitats with a Mediterranean climate. Life cycles of each host are also different: C. arvense is a perennial that emerges in spring and dies back in winter, while S. marianum is a winter annual that emerges in fall and dies in late spring. Thus, P. punctiformis from C. arvense may rarely encounter susceptible S. marianum plants in the field. However, since fungal spores can be produced routinely, there might be potential to use P. punctiformis for biological control of S. marianum. This would depend on understanding P. punctiformis-S. marianum interactions.