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First Report of Puccinia jaceae var. solstitialis Pycnia on Yellow Starthistle in the United States

The rust fungus Puccinia jaceae (Otth) var. solstitialis field isolate FDWSRU 84-71 (formerly TR 84--96) was first released in California for the biological control of yellow starthistle (YST; Centaurea solstitialis) in July 2003. This isolate was collected by S. S. Rosenthal in 1984, east of Yarhisar and Hafik (SIVAS), Turkey. It is macrocyclic and autoecious (1), completing its entire life cycle on YST. Observations were made in field plots west of Woodland, CA that had been inoculated on a monthly regimen between January and June of 2005. On February 22 and March 2, 2006, pycnia were observed in and around one of the plots (38°42.767′N, 121°53.732′W at an altitude of 57 m). Pycnia were yellow, flask shaped, and small (less than 100 μm in diameter), occurring in clusters on abaxial leaf surfaces or on petioles. DNA was isolated from pycnial and uredinial samples collected from the site and used for polymerase chain reaction amplification of the ITS2 region with P. jaceae specific primers. Sequences of amplicons from both samples were identical to FDWSRU 84-71 (GenBank Accession No. AF047728). Further amplification of pycnial DNA with PCR primers specific to the released P. jaceae isolate (2) produced the expected 851-bp amplicon. To our knowledge, this is the first report of pycnia from Puccinia jaceae var. solstitialis in the United States, suggesting that the YST rust is fully functional and completes its life cycle in California.

References: (1) D. B. O. Savile. Can. J. Bot. 48:1553, 1970. (2) L. F. Yourman and D. G. Luster. Biol. Control 29:73, 2004.