SEPTORIA CIRSII, A POTENTIAL BIOCONTROL AGENT OF CANADA THISTLE AND ITS PHYTOTOXIN - BETA-NITROPROPIONIC ACID

Septoria cirsii causes leaf spot of Canada thistle (Cirsium arvense L. ) and no other plant tested was susceptible to this pathogen. Because this pathogen possesses host specificity, and because it is so devasta ting to Canada thistle plants in the field, it is proposed for conside ration as abiological control agent. In culture, S. cirsii produced co pious amounts of a known phytotoxin which was identified as beta-nitro propionic acid. The toxin is inhibitory to seed germination, root elon gation and causes the typical symptoms of chlorosis and necrosis on th e leaves of Canada thistle which is one of the most toxin-sensitive pl ants of all of those tested.