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United States Department of Agriculture

Agricultural Research Service

Research Project: EVALUATION AND CHARACTERIZATION OF EXOTIC PLANT PATHOGENS FOR BIOLOGICAL CONTROL OF INTRODUCED, INVASIVE WEEDS Title: First report of leaf spot caused by Cladosporium herbarum on Centaurea solstitialis in Greece

Authors
item Berner, Dana
item Smallwood, Emily
item McMahon, Michael
item Luster, Douglas
item Kashefi, Javid - EUROPEAN BIO. CTRL. LAB

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 2006
Publication Date: April 1, 2007
Citation: Berner, D.K., Smallwood, E.L., Mcmahon, M.B., Luster, D.G., Kashefi, J. 2007. First report of leaf spot caused by Cladosporium herbarum on Centaurea solstitialis in Greece. Plant Disease. 91:463.

Interpretive Summary: Yellow starthistle (YST) is an invasive weed in California and the western U.S. and it is a target for biological control. In 2003 we found an epidemic of dying YST plants near Kozani, Greece. Plants had necrotic tan-brown leaf spots on most of the lower leaves and along the stems. Virtually all plants in a solid stand of YST (about 0.5 ha) showed disease symptoms. Diseased plants were sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD where the causative organism of the disease was isolated and identified as the fungus Cladosporium herbarum. At FDWSRU the disease was reproduced on other YST plants and the causative organism was again isolated from these plants. Results of host range tests will establish if this isolate of Cladosporium herbarum has potential as a biological control agent of YST in the USA.

Technical Abstract: In the summer of 2003, an epidemic of dying yellow starthistle (YST) plants was found near Kozani, Greece. Plants had necrotic tan-brown leaf spots on most of the lower leaves and on the decurrent leaf bases along the stems. Virtually all plants in a solid stand of YST (about 0.5 ha) showed disease symptoms. Diseased plants were sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. Based on culture growth (45 cm diam. after 2 wks at 25 deg C on malt extract agar), fungal morphology (1), and comparison to 21 ITS sequences in GenBank the organism was identified as Cladosporium herbarum (Pers.:Fr.) Link. (teliomorph= Davidiella tassiana (De Not.) Crous & U. Braun). Sixteen rosettes and bolted YST plants were inoculated with an aqueous suspension of spores (106 conidia ml-1) and placed in an environmentally controlled chamber at 25 deg C with 8 hr dew and 12 h light daily. Plants in the rosette stage were resistant, but the fungus was very aggressive on bolted plants. Within 4-6 days of inoculation necrosis developed on leaves and stems and then spread up the stems to capitula, often resulting in plant death. The fungus was reisolated from 16 bolted YST plants in two separate tests at FDWSRU and from eight of eight bolted inoculated plants at the European Biological Control Laboratory (EBCL) in Greece. Results of host range tests will establish if this isolate of Cladosporium herbarum has potential as a biological control agent of YST in the USA. To our knowledge this is the first report of a leaf spot caused by Cladosporium herbarum on YST.

Last Modified: 11/28/2014
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