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Physiology and Biochemistry

Induction of Systemic Aecial Infection in Canada Thistle (Cirsium arvense) by Teliospores of Puccinia punctiformis. R. C. French, Plant physiologist, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Bldg. 1301, Frederick, MD 21701; A. R. Lightfield, biological laboratory technician, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Bldg. 1301, Frederick, MD 21701, Current address: USDA-ARS, ERRC, MACS, Rm. 1123, 600 E. Mermaid Lane, Philadelphia, PA 19118. Phytopathology 80:872-877. Accepted for publication 19 February 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-872.

Systemic aecial infections of secondary Canada thistle shoots were observed 4?6 weeks after inoculation of root cuttings with teliospores of Puccinia punctiformis. Pretreatment with a stimulatory thistle root extract sometimes increased infection. Inoculation of dormant buds was the most effective way to induce infection of root cuttings. Aqueous soil extracts from potted Canada thistle plants stimulated teliospore germination. The active component in the soil was soluble in hexane, volatile, and was similar in nature to the hexane extract of steam-distilled Canada thistle roots. Optimum temperature range for stimulated teliospore germination on 1% agar was 16?20 C at 7 days.