Carposphere microbiome of pear harbours potential microbial biocontrol agents against Stemphylium vesicarium.

Stemphylium vesicarium, the causal agent of brown spot of pear (BSP), is responsible for important economic losses in the main pear-producing areas of Italy, particularly in Emilia Romagna, where the highly susceptible cultivar Abbé Fétel is widely cultivated. The pear microbiome is a rich reservoir of microorganisms, offering a valuable source of potential microbial biocontrol agents (mBCAs) against major diseases. Using a culturomics approach, eight isolates, selected over 1000 initial bacteria and yeasts isolated from the pear carposphere in orchards located in Emilia Romagna provinces, were tested for their antagonistic activity in vitro, using dual-culture assays, against a set of S. vesicarium strains. A bioassay on detached leaves was then conducted to assess their biocontrol potential in vivo. The candidate yeasts and bacteria were identified by sequencing the ITS regions and 16S rRNA gene, respectively. Antagonistic yeasts were identified as Aureobasidium pullulans, Metschnikowia sp., Rhodotorula babjevae, and Rhodotorula sp.; bacterial isolates belonged to the genera Bacillus, Pseudomonas, and Pantoea. In vitro antagonistic activity of the selected isolates was slightly variable, depending on the S. vesicarium strains tested. On detached leaves, both bacterial and yeast isolates significantly reduced BSP severity. Interestingly, results from in vitro assays were not always consistent with those from pear leaf bioassays, suggesting different biocontrol mechanisms. Further investigations are needed to identify the mechanisms of action of these mBCA candidates against S. vesicarium. Finally, in planta assays are currently ongoing to assess their ecological behaviour and potential for effective BSP control. This study was funded by the Emilia Romagna region within Reg. Law 17 del 27/10/2022. Type of operation “Urgent interventions to support the agricultural, agrifood, fishing and reclamation sectors” Art. 1 “Interventions for innovation in the agricultural and agri-food sector” – Project “A.MA.PERO - Approcci innovativi indirizzati a contrastare la Maculatura bruna del Pero”. Research was conducted in collaboration with the framework of the EU-COST action CA22158 (MiCropBiomes: Exploiting Plant-Microbiomes Networks and Synthetic Communities to improve Crops Fitness).