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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 rust caused by Puccinia carduorum on Italian thistle in Tunisia

Authors
item Mejri, Dorsaf - INSTITUT AGR. DE TUNISIE
item Souissi, Thouraya - INSTITUT AGR. DE TUNISIE
item Berner, Dana

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2007
Publication Date: January 1, 2008
Citation: Mejri, D., Souissi, T., Berner, D.K. 2008. First report of rust caused by Puccinia carduorum on Italian thistle in Tunisia. Plant Disease. 92:174.

Interpretive Summary: Italian thistle is a common weed in rangelands, pasturelands, and cereal crops in Tunisia and is also a problematic invasive weed in the western United States and a target of biological control efforts. In surveys conducted in northern Tunisia, from 2003 to 2005, eighty-five isolates of a rust fungus were collected from Italian thistle. Spores of all isolates of the rust were similar in morphology, and their characteristics matched the description of Puccinia carduorum. Comparison of DNA sequences of a representative isolate of the fungus matched (97%) other sequences from P. carduorum. Spores were used to inoculate six plants in each of three developmental stages: 2-5, 6-8, and >8 leaf stage. All plants in each stage became diseased and produced spores. Plants in the 2-5 leaf stage were more severely diseased than plants in the other stages. To our knowledge, this is the first report of Puccinia carduorum parasitizing Italian thistle in Tunisia.

Technical Abstract: Italian thistle (Carduus pycnocephalus L.), family Asteraceae, is a common weed in rangelands, pasturelands, and cereal crops in Tunisia where it is rapidly spreading and becoming agriculturally important due to its competitive ability. It is also a problematic invasive weed in the western United States and a target of biological control efforts. In surveys conducted in northern Tunisia, from 2003 to 2005, eighty-five isolates of a rust fungus were collected from Italian thistle. Urediniospores and teliospores of all isolates of the rust were similar in morphology, and their characteristics matched the description of Puccinia carduorum. Comparison of the ITS1, 5.8S ribosomal DNA, and ITS2 regions of a representative isolate with ITS sequences in GenBank indicated that the rust sequences were 97% similar to sequences from P. carduorum from Carduus nutans. Urediniospores were used to inoculate rosettes of six plants in each of three developmental stages: 2-5, 6-8, and >8 leaf stage. All plants in each stage became diseased and produced uredinia. Plants in the 2-5 leaf stage were more severely diseased than plants in the other stages. To our knowledge, this is the first report of Puccinia carduorum parasitizing Italian thistle in Tunisia.

Last Modified: 11/24/2014
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