Fungal community and toxigenic taxa in chestnut fruits in postharvest conditioning process and storage.

BACKGROUND: Chestnut fruit quality is affected by fungal contamination. The study of the patterns of contamination in the postharvest is crucial to individuate the critical phases and propose solutions. To understand how fungal colonization varies on fruits, the composition of mycobiota was investigated in postharvest handling and in between tissues (shell and kernel). RESULTS: Fungal sequences were clustered into 308 operational taxonomic units (OTUs). Biodiversity was higher in shell than kernel tissues. Results evidenced the risk of new contamination in specific phases such as the 'cold bath' and storage. Genera known as mycotoxin producers were detected in all phases. Specifically, 47 OTUs belonging to Penicillium, eight to Fusarium and two to Aspergillus genera were identified. While Fusarium spp. was sensitive to 'warm bath' phase, Penicillium spp. was largely insensitive and accumulated in storage conditions. Surprisingly, Aspergillus spp. was poorly represented. Aflatoxin, ochratoxin A, fumonisins and T-2/HT-2 detection was performed for shell and kernel, and process phases. Higher contamination was observed on shell than in kernel samples. While aflatoxins were within the European Union (EU) limits for dry fruits, Ochratoxin exceeded the EU limits. The present study represents the first report of fumonisins and T-2/HT-2 detection in chestnuts. CONCLUSION: Fungal contamination taxa is high in chestnut fruits following postharvest handling and storage. A parametrization of process phases such as the 'warm bath' is functional to reduce the risk for some taxa. For other spoilage and mycotoxigenic genera strict sanitation procedures of equipment and water must be individuated and implemented to reduce their impact. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Hybrid de novo genome assembly and comparative genomics of three different isolates of Gnomoniopsis castaneae.

The first genome assemblies of Gnomoniopsis castaneae (syn. G. smithogilvyi), the causal agent of chestnut brown rot of kernels, shoot blight and cankers, are provided here. Specifically, the complete genome of the Italian ex-type MUT401 isolate was compared to the draft genome of a second Italian isolate (GN01) and to the ICMP 14040 isolate from New Zealand. The three genome sequences were obtained through a hybrid assembly using both short Illumina reads and long Nanopore reads, their coding sequences were annotated and compared with each other and with other Diaporthales. The information offered by the genome assembly of the three isolates represents the base of data for further application related to -omics strategies of the fungus and to develop markers for population studies at a local and global scale.

Impact of 'brown rot' caused by Gnomoniopsis castanea on chestnut fruits during the post-harvest process: critical phases and proposed solutions.

BACKGROUND: The brown rot fungus, Gnomoniopsis castanea, is the main organism responsible for the outbreak of chestnut postharvest decay that is threatening the sustainability of the chestnut market in Europe. Currently, no specific strategy is available to mitigate the impact and remediate the high losses of fruits in postharvest storage. In the present study, the different phases of chestnut handling in a standard facility plant were analyzed by evaluating the amount of fruit rot and infection by G. castanea at each phase. RESULTS: The warm bath (48 °C) was identified as the critical phase, requiring strict parametrization to effectively inactivate G. castanea in fruits. Laboratory tests indicated that maintaining fruits at 50 °C for a maximum of 45 min provided optimal conditions to completely inactivate G. castanea inoculum during postharvest handling. However, the warm bath at 50 °C and over was not effective in inactivating the complex of fungal taxa responsible for contamination and development of molds. Higher temperatures and extended treatment times caused significant losses in fruit quality, as indicated by taste panel evaluation. Upscaling of postharvest facilities is discussed and critically evaluated. CONCLUSION: The warm bath (50 °C for 45 min) is effective in completely inactivating G. castanea in fruits but did not reduce the impacts of the complex of molds responsible for external contamination and mycotoxin production. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.