Identification and characterisation of microbial isolates from pear carposphere and their possible role in brown spot disease management

Brown spot of pear (BSP) caused by Stemphylium vesi¬carium (Sv) is one of the most important fungal diseases in Europe, as it may cause more than 90% yield losses. In Abate Fétel pear orchards, located in five Emilia Romagna provinces (Modena, Bologna, Ferrara, Ravenna and Forlì- Cesena) and under different pest management strategies (integrated or organic), studies on the carposphere micro¬biota helped us to identify bacterial and yeast epiphytes suitable to be exploited as microbial biocontrol agents (mBCAs) against Sv. During the summer of 2023, a total of 359 bacterial and 233 yeast strains were isolated and tested in vitro against Sv DLS2021 (UNIMORE collection). The dual-plate assay showed a reduction of Sv mycelial growth higher than 65% for nine bacteria and nine yeasts, later taxonomically identified. Based on ITS regions (spanning ITS1, 5.8S rRNA and ITS2) sequencing, antagonistic yeasts were attributed to the species Aureobasidium pullulans, Metschnikowia pulcherrima, Rhodotorula babjevae, Rho¬dotorula glutinis, and Sporobolomyces patagonicus. For bacterial isolates, the partial sequencing and NCBI blast of the 16s rRNA gene confirmed their identity as members of the genera Bacillus, Pseudomonas, Pantoea, and Erwinia. Putative mBCAs were checked for their biocontrol activ¬ity in vivo on detached fruits, under laboratory conditions. The tested bacterial and yeast isolates were able to reduce the BSP lesion severity on fruits by up to 55%. Our study may help to understand the epidemiological importance of culturable microbiota residing on the pear carposphere and the selection of effective mBCAs suitable for implementing sustainable management of BSP. 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, agri-food, 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”.