Innovation in pre- and post-harvest biocontrol: novel strategies against Botrytis cinerea for grape preservation

Driven by the demand for sustainable agriculture, biocontrol is emerging as a crucial alternative to chemical fungicides for crop protection. This strategy focuses on the use of living microorganisms, their metabolites or other natural compounds, to counteract plant diseases and preserve food quality. A critical problem in the wine industry is Botrytis cinerea infection, which compromises grape quality. Current management is based on chemical fungicides, but their use is limited in pre-harvest stages to avoid residues in the final product, pushing towards natural solutions such as biocontrol. However, the number of microorganisms registered as active substances in the European Union is still limited, highlighting the need for improved selection and application processes [1].

In this context, the purpose of this work is to assess the performance of new microbial isolates (grapevine wood endophytes) as bioprotective microorganisms and comparing them with commercial agents already in use, such as Metschnikowia fructicola (currently reclassified as M. pulcherrima) [2,3] and Aureobasidium pullulans. The study firstly focuses on post-harvest application, with particular attention to the storage phase, which represents a critical moment for the protection of fruit quality.

The bio-protective potential of some bacterial isolates, primarily Actinobacteria [4], previously selected through in vitro assays [5], was evaluated on grape bunches. Initial trials conducted under controlled conditions (laboratory-scale treatment of table grapes with controlled Botrytis cinerea infections) allowed to evaluate the ability of different microbial strains to colonize the grape surface and maintain viability during storage, essential traits for effective biocontrol agents. Monitoring of disease incidence and severity indices revealed a significant reduction in the growth of Botrytis cinerea mycelium on treated bunches. In this context, the tested isolates demonstrated biocontrol efficacy comparable to that of reference microorganisms known for their bioprotective capacities[1], which were confirmed.

Further trials under industrial conditions (withering warehouses for passito wine production) were carried out for determining the most suitable application conditions to reduce the development of naturally present Botrytis cinerea. The experiments, conducted at two different wineries, tested the effectiveness of the microorganisms, both alone and in microbial consortia containing multiple strains, also considering the use of adhesives to improve the effectiveness of the treatments.

The results, particularly encouraging in contexts characterized by high botrytis pressure, indicate promising application as an alternative to chemical control.

1. Sellitto, V.M.; Zara, S.; Fracchetti, F.; Capozzi, V.; Nardi, T. Microbial Biocontrol as an Alternative to Synthetic Fungicides: Boundaries between Pre- and Postharvest Applications on Vegetables and Fruits. Fermentation 2021, 7, 60, doi:10.3390/fermentation7020060.

2. Sipiczki, M. Metschnikowia Pulcherrima and Related Pulcherrimin-Producing Yeasts: Fuzzy Species Boundaries and Complex Antimicrobial Antagonism. Microorganisms 2020, 8, 1029.

3. Sipiczki, M. Taxonomic Revision of the Pulcherrima Clade of Metschnikowia (Fungi): Merger of Species. Taxonomy 2022, 2, 107–123, doi:10.3390/taxonomy2010009.

4. Bertazzoli, G.; Nerva, L.; Chitarra, W.; Fracchetti, F.; Campedelli, I.; Moffa, L.; Sandrini, M.; Nardi, T. A Polyphasic Molecular Approach to Characterize a Collection of Grapevine Endophytic Bacteria with Bioprotective Potential. J. Appl. Microbiol. 2024, lxae050, doi:10.1093/jambio/lxae050.

5. Sandrini, M.; Nerva, L.; Moffa, L.; Giudice, G.; Favaretto, F.; Chitarra, W. Actinomycetes Come to Rescue of Viticulture Sustainability. In Proceedings of the Convegno AISSA# under40; Sassari, 2021; Vol. Poster.