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Importance de la cassiicoline en tant qu'effecteur de la Corynespora Leaf Fall (CLF) chez l'hévéa : Développement d'outils pour le contrôle de la maladie

Abstract : Rubber tree (Hevea brasiliensis) is the only source of commercial natural rubber. The “Corynespora Leaf Fall” (CLF) disease, caused by the fungus Corynespora cassiicola, has become over the last 50 years a very serious problem in the Asian and African rubber producing countries. Currently, the main methods to face the problem are the uprooting of the most susceptible cultivars and chemical treatments in case of severe outbreaks. However, the number of cultivars affected by the disease keeps increasing, and the selection of new cultivars, both tolerant and high yielding, is urgent. In this study, the gene encoding cassiicolin, a toxic glycosylated protein secreted by C. cassiicola, was characterized and its diversity analyzed. The analysis of three C. cassiicola isolates with contrasted levels of aggressiveness revealed the presence of identical cassiicolin genes in the highly and moderately aggressive isolates but none in the isolate of mild aggressiveness. The levels of aggressiveness were correlated to the cassiicolin gene transcript levels. The cassiicolin gene was preferentially expressed in the early phase of the infection. Analysis of the cassiicolin gene diversity among isolates from various host and various geographical origins revealed the existence of at least six protein isoforms (Cas1 to Cas6). The genetic structure of the isolates based on neutral markers was closely related to the genetic structure based on the cassiicolin gene. The isolates sampled on rubber tree were grouped in several specialized clades, including one clade regrouping all the Cas1 isolates, which were the most aggressive on rubber tree. However, 58 % of the isolates seemed to be deprived of cassiicolin gene, although some of them generate moderate symptoms on rubber tree, suggesting the existence of other effectors. Endophytic C. cassiicola isolates were found in asymptomatic rubber tree leaves from Brazil, a region were CLF outbreak was never reported. No expression of the cassiicolin genes carried by these isolates could be detected in interaction with rubber tree. In addition, we found that the Trichoderma and Xylaria species, all fungal endophytes of rubber tree, were antagonists of C. cassiicola, in vitro. This work opens new perspectives for the control of CLF (through early diagnosis, selection of tolerant clones, or biocontrol).
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https://tel.archives-ouvertes.fr/tel-00741952
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Submitted on : Monday, October 15, 2012 - 3:32:42 PM
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  • HAL Id : tel-00741952, version 1

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Marine Deon. Importance de la cassiicoline en tant qu'effecteur de la Corynespora Leaf Fall (CLF) chez l'hévéa : Développement d'outils pour le contrôle de la maladie. Sciences agricoles. Université Blaise Pascal - Clermont-Ferrand II, 2012. Français. ⟨NNT : 2012CLF22239⟩. ⟨tel-00741952⟩

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