Authors
T.
Widmer
,
European Biological Control Laboratory, USDA/ARS, Campus International de Baillarguet, CS 90013, Montferrier sur Lez, 34988 St. Gely du Fesc, France
;
L.
Castlebury
and
A.
Rossman
,
Systematic Botany and Mycology Laboratory, USDA/ARS, 10300 Baltimore Blvd., Beltsville, MD 20705, USA
Phoma exigua Desm. (teleomorph Didymella exigua (Niessl) Sacc.) was isolated from wilted Centaurea solstitialis L. (yellow starthistle) plants displaying necrosis of the crown that were found near Krasnodar, Russia. The fungus was identified using morphological and cultural characteristics (1,2) and confirmed by sequencing the complete internal transcribed spacer region of the nuclear rDNA (GenBank Accession No. AY089978). P. exigua is a relatively common soilborne fungus that is weakly pathogenic on a diverse range of primarily dicotyledonous plants throughout the world (1). To our knowledge, it has never been reported previously on members of the genus Centaurea. Yellow starthistle is native to eastern Europe and the Mediterranean Region, and is now a noxious weed in North America for which P. exigua is being investigated as a potential biological control agent. Repeated pathogenicity studies (N = 30) resulted in a mortality of 80 and 93% within 7 days when 1-week-old seedlings were transplanted in soil infested with P. exigua-colonized wheat seed at rates of 6.7 and 10% (vol/vol), respectively. Symptoms of the seedlings included necrosis of the stem and wilting of the seedling. Pycnidia were observed in the roots of dead seedlings. The isolate of P. exigua has been deposited as a dried specimen at the U.S. National Fungus Collections, Beltsville, MD (BPI 841766) and as a living culture at the CBS collection in Utrecht, Netherlands (CBS 110211).
References: (1) G. Morgan-Jones and K. B. Burch. Mycotaxon 32:477, 1988. (2) H. A. Van Der Aa et al. Persoonia 17:435, 2000.
