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., Souissi, T., Berner, D.K. 2010. Evaluation of Puccinia carduorum for biological control of Italian thistle (Carduus pycnocephalus). Biocontrol Science and Technology. 20:787-790. Interpretive Summary: During surveys for diseases of weeds in northern Tunisia, a rust fungus was found to be widespread on Italian thistle. This weed is problematic in Tunisia and is a target for biological control. Tests of the fungus on Italian thistle showed that younger plants with 8 leaves or less were very susceptible to the fungus. When the fungus was applied several times to the weeds, as would occur in nature, there was a reduction in weights of the roots and above-ground shoots. Each successive application of the fungus to the weeds reduced these weights even more. Tests of the fungus on artichoke and safflower showed that these economically important plants were not susceptible to the fungus. Because the fungus is native to Tunisia, extensive host-range testing is not necessary to safely use the fungus in Tunisia. Rather, there are possibilities to increase spores of the fungus to augment naturally occurring levels of spores and achieve control in areas difficult for mechanical cultivation and/or impractical for herbicide use, e.g., pasturelands, orchards, and vegetable production areas. This is the first report of this fungus parasitizing Italian thistle in Tunisia.
Technical Abstract: The rust fungus Puccinia carduorum is a candidate for biological control of Italian thistle (Carduus pycnocephalus). In Tunisia, rusted Italian thistle has been found in many fields during surveys conducted in the north region of the country. The pathogenicity of Puccinia carduorum was evaluated under greenhouse conditions and it was found to be most aggressive on younger growth stages of the weed (2-5 leaves) and least aggressive on old growth stages (more than 8 leaves). 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 not able to parasitize artichoke and safflower plants. Because the rust is endemic to Tunisia, extensive host-range testing is not necessary to to safely use the fungus in Tunisia. Rather, there are possibilities to increase urediniospores of the rust to augment naturally occurring levels of inoculum and effect control in areas difficult for mechanical cultivation and/or impractical for herbicide use, e.g., pasturelands, orchards, vegetable production areas. This is the first report of P. carduorum parasitizing C. pycnocephalus in Tunisia.