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Étude de la microflore colonisant les tissus ligneux de Vitis vinifera : Intérêt pour le développement d’agents de biocontrôle contre une maladie du bois de la vigne, l’esca

Abstract : Grapevine trunk diseases (GTDs) such as esca are of major concern for viticulture worldwide. In Tunisia, knowledge about the symptoms of this disease and the microflora associated with, is still incomplete despite their ability to cause considerable damage to vineyards. In France, around 13% of whole vineyard is unproductive because of GTDs, and no effective treatment currently exists. In that context, the objectives of the present PhD study were: (i) to characterize the fungal microflora inhabiting the wood tissues of Tunisian esca-foliar symptomatic vines in order to identify the pathogens responsible for wood decay. (ii) To investigate the bacterial microflora colonizing the wood tissues of Tunisian grapevines cv. Muscat d’Italie in order to find a suitable Biological Control Agent (BCA) that can be applied to vineyards. First, in order to better characterize the microflora colonizing the wood tissues of vine, samples were collected from 10 vineyards in the north of Tunisia. Fungal isolates were obtained from trunk of grapevines showing decline, small and distorted leaves and chloroses. To identify the isolated fungal species, sequencing of the Internal Transcribed Spacer region of the rDNA was performed (ITS1 and ITS4 primers). Three pathogens, i.e. Lasidiodiplodia pseudotheobromae, Neofusicoccum parvum and Schizophyllum commune, described in the literature as involved in GTDs were isolated for the first time in Tunisia. Their pathogenicity was confirmed in planta. Moreover, the coinoculation of these 3 fungi in planta, showed that they displayed a competitive inhibition effect on each other. In another study, two others pathogens involved in GTDs, i.e. Phomopsis viticola and Diploidia seriata were also isolated from the same region. This PhD also aimed at identifying the bacterial microflora inhabiting the wood tissues of escafoliar symptomatic vines, i.e. necrotic and non-necrotic wood, using microbiological and molecular approaches. Complex bacterial communities, as shown by Single-Strand Conformation Polymorphism (SSCP) analyses, colonize both types of wood tissues. After isolation, the 19 most abundant cultivable strains were sequenced (16S rRNA and rpoB genes) and identified as belonging to four genera: Bacillus, Pantoea, Pseudomonas and Curtobacterium. They were then screened for their in vitro antagonistic traits against the three pathogenic fungi L. pseudotheobromae, N. parvum and S. commune. Based on the results obtained, two bacterial strains were selected: B. subtilis (strain B6) and Pantoea agglomerans (strain S5), respectively isolated from Tunisian and French grapevines. They were then tested in planta on young vines of cv Muscat d’Italie and Cabernet Sauvignon against two fungal pathogens involved in GTDs, i.e. N. parvum (isolated from Tunisian wood) and Phaeomoniella chlamydospora (isolated from French vines). Young vines of both cultivars were inoculated by B. subtilis B6, P. agglomerans S5 or the combination of B6+S5, singly or in combination with N. parvum and P. chlamydospora. In terms of plant protection, the most efficient condition to reduce in planta necrosis caused by the fungal pathogens in the two cultivars was the combination of the two bacteria. However, bacterial treatments were significantly more efficient to reduce necrosis caused by N. parvum or P. chlamydospora in Muscat d’Italie than in Cabernet Sauvignon.
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Awatef Rezgui. Étude de la microflore colonisant les tissus ligneux de Vitis vinifera : Intérêt pour le développement d’agents de biocontrôle contre une maladie du bois de la vigne, l’esca. Mycologie. Université de Bordeaux; Université de Tunis El Manar, 2016. Français. ⟨NNT : 2016BORD0449⟩. ⟨tel-02063177v2⟩

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