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Estimation du potentiel de résistance de Botrytis cinerea à des biofongicides

Abstract : Gray mould, caused by Botrytis cinerea, is a severe disease on a wide range of crops. Disease control generally relies on chemicals, although biological control strategies have been intensively studied over the last decades. This pathogen can withstand a wide variety of fungitoxic compounds including fungicides and natural molecules. This capacity to adapt to different stress might, potentially, compromise the durability of biological control methods. The global purpose of that work was to estimate the potential of B. cinerea to overcome the efficacy of biological control agents. Knowledge on the potential development of resistance to biological control agents can help to devise or improve resistance management strategies. In this work, efforts have been focused on the antibiotic pyrrolnitrin produced by various bacteria described as potential biological control agents against B. cinerea. The specific objectives of the study were (i) to evaluate the diversity in susceptibility to pyrrolnitrin among natural population of B. cinerea, (ii) to estimate the risk of loss of efficacy of pyrrolnitrinproducing biological control agent due to selection pressure exerted by pyrrolnitrin and (iii) to study the mechanism of resistance to pyrrolnitrin in B. cinerea. An important range of sensitivity to pyrrolnitrin with an 8.4-fold difference in EC50 values between the most sensitive and the least sensitive isolates was observed within the 204 isolates tested. The production of 20 generations, for 4 isolates of B. cinerea, on increasing doses of pyrrolnitrin, resulted in the development of mutants of B. cinerea with high levels of resistance to the antibiotic and a reduced sensitivity in vitro to the pyrrolnitrin-producing Pseudomonas chlororaphis PhZ24. Comparison of the pyrrolnitrin-resistant mutants and their sensitive parent isolates for mycelial growth, sporulation and aggressiveness on plant tissues revealed that the high level of resistance to pyrrolnitrin has resulted in a high fitness cost. Additional cytohistological investigations revealed that while the sensitive isolate spread throughout the petiole and rapidly invaded the stem via the abscission zone, the pyrrolnitrinresistant mutant failed to extend beyond petiole to invade the stem. Moreover, the pyrrolnitrin-resistant mutant formed abnormal mycelium and chlamydospore-like cells. The comparison of resistance to pyrrolnitrin and to the iprodione fungicide in B. cinerea revealed that fungicide pressure exerted on the fungus is able to build-up resistance to pyrrolnitrin. Comparison of sequences of the osmosensing class III histidine kinase encoding gene bos1 revealed different mutations in pyrrolnitrin- and iprodione-resistant mutants. However, resistance to pyrrolnitrin and to iprodione was not systematically associated with a point mutation in the Bos1 gene. Finally, no changes were observed in the allele size at nine microsatellite loci whatever the four selective pressure endured by the fungus despite their phenotypic changes. This study provides evidence that a fungal plant pathogen is able to gradually build-up resistance to an antibiotic produced by a biocontrol agent
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  • HAL Id : tel-02823602, version 1
  • PRODINRA : 37928

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Sakhr Ajouz. Estimation du potentiel de résistance de Botrytis cinerea à des biofongicides. Sciences agricoles. Université d'Avignon et des Pays de Vaucluse, 2009. Français. ⟨tel-02823602⟩

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