Septoria cirsii, a potential biocontrol agent of Canada thistle and its phytotoxin-ß-nitropropionic acid

Septoria cirsii causes leaf spot of Canada thistle (Cirsium arvense L.) and no other plat tested was susceptible to this pathogen. Because this pathogen possesses host specificity, and because it is so devastating to Canada thistle plants in the field, it is proposed for consideration as a biological control agenet. In culture, S. cirsii produced copious amounts of a known phytotoxin which was identified as ß-nitropropionic acid. The toxin is inhibitory to seed germination, root elongation and causes the typical symptoms of chlorosis and necrosis on the leaves of Canada thistle which is one of the most toxin-sensitive plants of all of those tested. © 1993.