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Title: Evaluation of Puccinia carduorum for biological control of Carduus pycnocephalus in Tunisia

Author
item MEJRI, DORSAF - Tunisian National Institute Of Agronomy
item Berner, Dana
item SOUISSI, THOURAYA - Tunisian National Institute Of Agronomy

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2010
Publication Date: 5/12/2010
Citation: Mejri, D., Berner, D.K., Souissi, T. 2010. Evaluation of Puccinia carduorum for biological control of Carduus pycnocephalus in Tunisia. Biocontrol Science and Technology. 20(8):787-790.

Interpretive Summary: The rust fungus Puccinia carduorum is a candidate for biological control of Italian thistle in the USA. In Tunisia, rusted Italian thistle has been found in many fields during surveys conducted in the north of the country. The pathogenicity of Puccinia carduorum was evaluated under greenhouse conditions and it was found to be more aggressive on leaf growth stages of young weeds than on old growth stages. Repeated inoculations of the thistle with spores of P. carduorum under greenhouse conditions reduced the growth of roots and rosettes of the weed, compared to controls. Results of tests of specificity conducted under greenhouse conditions on the weed showed that P. carduorum was unable to parasitize artichoke and safflower plants. Because the rust is endemic to Tunisia, extensive host-range testing is not necessary to safely use the fungus in Tunisia. Augmenting naturally occurring levels of spores may lead to effective control of Italian thistle where mechanical or chemical options are impractical.

Technical Abstract: The rust fungus Puccinia carduorum is a candidate for biological control of Carduus pycnocephalus in the USA. In Tunisia, rusted C. pycnocephalus has been found in many fields during surveys conducted in the north of the country. The pathogenicity of Puccinia carduorum was evaluated under greenhouse conditions and it was found to be more aggressive on 2-5 leaf growth stages of the weed than on old growth stages (> 8 leaf). Repeated inoculations of the thistle with urediniospores of P. carduorum, simulating secondary cycles of the rust, under greenhouse conditions reduced the growth of roots and rosettes of the weed. Each successive inoculation reduced root and shoot dry weights below those of the non-inoculated control. After four inoculations, root and shoot dry weights were reduced by 66 percent and 70 percent, respectively, compared to controls. Results of tests of specificity conducted under greenhouse conditions on the weed with species of economic importance, i.e., artichoke and safflower, showed that P. carduorum was unable to parasitize artichoke and safflower plants. Because the rust is endemic to Tunisia, extensive host-range testing is not necessary to safely use the fungus in Tunisia. Rather, there are possibilities to increase urediniospores of the rust to augment naturally occurring levels of inoculum that may lead to effective control where mechanical or chemical options are impractical.