Ecological relations inside plant microbiota can improve the efficacy of biocontrol agents: The case of Pichia anomala strain K against Botrytis cinerea on apple

Pichia anomala strain K is a Biological Control Agents (BCA) against apple two postharvest pathogens (Penicillium spp. and Botrytis cinerea). Progress have been made during the past two decades to understand its modes of action through various studies. To further improve and stabilize its efficacy, Massart et al. (2015) suggested to focus on benefic interactions inside host microbiota to favor BCAs. Indeed, once applied, BCAs will face a complex microbiota where ecological interactions such as competition, parasitism, mutualism and commensalism occur. In this study, we investigated the potential of apple microbiota to improve the efficacy of strain K against B. cinerea. Sampling were carried out in Belgium, by harvesting fruits of fifteen apple varieties grown in four disease management practices [no phytosanitary treatment (conservation orchard), light-organic, organic and conventional]. Epiphytic microbiota were collected by 15 min sonication and by washing apples with a phosphate buffer (pH=7.4). Apple washing solutions were stored at -80°C to generate a microbiota bank made up with eighteen different microbiota. The quantity of microorganisms (bacteria and fungi/yeast) in each microbiota type was first estimated by plating. Afterward, biological assays on wounded apple fruits have been carried out by co-inoculating each apple microbiota with the strain K, then with B. cinerea 24h later. The results show that apple skin harbors around 2 x104 ± 1,5 x104 microorganisms/cm2. The biological assays revealed that the apple microbiota can either raise till 100%, drop or have no effect on the efficacy of strain K. Thanks to next generation sequencing that makes the microbiota profiling possible, studies are ongoing to identify ecological strains/species or groups of taxa which are benefic to the strain K efficacy.