V246LRPR

3841

12 mai 2021 08:23

12 mai 2021 08:36

Biocontrol using biocontrol agents (BCA) is a sustainable way to manage postharvest diseases. Nevertheless, their reliability (stability of efficacy) must still be improved to reach efficacy of synthetic chemical pesticides. Indeed, when BCA are applied on the plant surface, they meet contrasted microbial community in which ecological relationships take place, thus potentially interfering with their efficacy and stability. Understanding better the role of fruit microbiota composition in the disease development and in the efficacy of BCA is an emerging research area. This could allow the isolation of more beneficial strains or the identification of molecules that modulate host microbiota to favour BCA and to limit disease development. In this thesis, apple microbiota was deeply characterized and used in situ to improve the efficacy and stability of Pichia anomala strain K, a BCA against Botrytis cinerea rot. At first, several protocols to harvest the epiphytic microbiota were tested and compared. Results showed that a first wash harvested one third of culturable microorganisms, and that three successive washes harvested around 80% of them. There were significant differences between protocols, thus inducing potential bias among studies using different protocols to study the epiphytic microbiota. However, this bias was offset by pooling the successive washes, that besides increased overall microbial richness. Then, the metagenome of apple fruit microbiota was studied by shotgun highthroughput sequencing (HTS) on three symptomless samples of apple fruit Pinova variety. Results showed a very high fungal (79.0 %) and bacterial (13.8 %) diversity. The prevalent phyla were Ascomycota for fungi and Bacteroides for bacteria. Genera of known apple postharvest pathogens and known BCA were identified. The functional analysis showed important genes potentially involved in biocontrol activity. On the other hand, the incompleteness of current databases and the complexity of the analysis limited the complete exploitation of the results and are blockages of using such technic currently. Finally, contrasted apple microbiomes were harvested and studied to identify beneficial strains and molecules to control Botrytis cinerea. Eighteen apple microbial communities (representing fifteen cultivars and four management practices) were harvested and characterized by HTS of 16s rRNA gene and Internal Transcript Spacer (ITS) amplicons. The biocontrol efficacy against B. cinerea of these microbiotas applied alone or with a BCA was also evaluated and the metabolisation of 190 carbon sources was studied. Results showed that apple microbiota is diversified and contrasted at taxonomic level, biocontrol efficacy and carbon source metabolisation. Certain microbiota significantly raised the strain K efficacy up to 100%. The alpha diversity of the apple microbiota was not correlated to the biocontrol efficacy. Coclustering of Spearman correlations were used to drive the isolation of promising beneficial strains (BCA candidates or helper strains supporting BCA efficacy) and molecules allowing better control of the pathogen. Biocontrol efficacy of the new strains and molecules was further confirmed in vivo. Results of this work can contribute to increase the reliability of BCA in real condition.

None

• AB - Utile à l'AB
• FREDO conservation des productions
• FREDO lutte
• FREDO qualité des produits
• FREDO technologie et innovation
• GEO Belgique
• GEO Wallonie
• biocontrol
• pomme

2020-10-13

13 octobre 2020