Chestnut rots: disease incidence and molecular identification of causal agents

Dupla diplomação com a Université Libre de TunisChestnut fruits are popular fruits commercialized as fresh or processed ready to be used as products. Because of its high moisture and suitable nutrient content, the chestnut kernel has the potential to support the growth of a wide spectrum of spoilage fungi. The major postharvest problems associated with stored chestnut fruits are rots, which result in major losses in fruit quality. Although the empirical knowledge determines a high level of rot in Portuguese chestnuts, there are no scientific studies on the incidence and severity of the problem, and the causal agents have never been identified. This knowledge is of the utmost importance and urgency for industry and retailers to correctly address the issue, in an effort to reduce yield loss due to rot. The aims of this work were: i) to determine the incidence, abundance and diversity of rots in three chestnut varieties of Trás-os-Montes – Judia, Longal and Martaínha – at different postharvest stages of storage and processing, and ii) to identify the main potential agents of rots. For this purpose chestnuts were internally and externally inspected for presence of damages, infestation and infection. Samples from variety Martaínha were identified as the most resistant to fungal growth, while samples from variety Longal were less resistant to fungal growth and infestation. A high diversity of species has been molecularly identified by sequencing the ITS region: 37 different species belonging to 16 genera. The dominant fungal species found with high frequency were Mucor racemosus f. sphaerosporus (24.2% of frequency), Penicillium brevicompactum (16.7%) and Penicillium thomii (causal agents of green rot; 13.9%), Ciboria batschiana (the causal agent of black rot; 10.6%) and Botrytis cinerea (the causal agent of grey rot10.6%). Gnomoniopsis smithogilvyi, the causal agent of brown rot, was also identified with a frequency of 6.4%. The results show that the causal agents of various chestnut rots already identified in other countries are also present in Portuguese nuts. Studies must follow with the aim of developing control measures against the identified rot-causing fungi.A castanha é um fruto popular comercializado e consumido tanto em fresco como processado. Devido à sua elevada humidade e teor de nutrientes, a castanha tem o potencial de permitir o crescimento de um amplo espectro de fungos de deterioração. Os principais problemas pós-colheita associados à castanha armazenada são as podridões, que resultam em grandes perdas na qualidade dos frutos. Embora o conhecimento empírico evidencie um alto nível de podridão nas castanhas portuguesas, não existem estudos científicos sobre a incidência e gravidade do problema, e os agentes causais nunca foram identificados. Esse conhecimento é da maior importância e urgência para a indústria e os comerciantes resolverem o problema adequadamente, no sentido de reduzirem as perdas de rendimento devido à podridão. Os objetivos deste trabalho foram: i) determinar a incidência, abundância e diversidade de podridões em três variedades de castanha de Trás-os-Montes - Judia, Longal e Martaínha - em diferentes estágios pós-colheita de armazenamento e processamento; e ii) identificar os principais agentes causais das podridões. Para esse fim, as castanhas foram inspecionadas interna e externamente quanto à presença de danos, infestações e infeções. Amostras da variedade Martaínha foram identificadas como as mais resistentes ao crescimento de fungos, enquanto amostras da variedade Longal foram menos resistentes ao crescimento e infestação de fungos. Uma alta diversidade de espécies de fungos foi identificada molecularmente através da região ITS: 37 espécies diferentes pertencentes a 16 géneros. As espécies dominantes encontradas com alta frequência foram Mucor racemosus f. sphaerosporus (24.2% de frequência), Penicillium brevicompactum (16.7%) e Penicillium thomii (13.9%) (agentes causais de podridão verde), Ciboria batschiana (agente causal da podridão negra; 10.6%) e Botrytis cinerea (agente causal da podridão cinzenta; 10.6%). Gnomoniopsis smithogilvyi, agente causal da podridão castanha, também foi identificado, com frequência de 6.4%. Estes resultados mostram que os principais agentes causais das podridões da castanha se encontram também nas castanhas portuguesas. Estão em curso estudos para desenvolvimento de métodos de controlo des fungos nas castanhas.This work was developed under the scope of the project “ValorCast - Valorização da castanha e otimização da sua comercialização”, ref. PDR2020-101-032030. Funded by Fundo Europeu Agrícola de Desenvolvimento Rural (FEADER) and Portuguese Government, under the scope of Ação 1.1 «Grupos Operacionais», Medida 1. «Inovação», PDR 2020 – Programa de Desenvolvimento Rural do Continente

Impact of cultivar, processing and storage on the Mycobiota of european chestnut fruits

Sweet chestnut fruits are popular fruits commercialized as fresh or processed ready-to-eat products. The major post-harvest problems associated with stored chestnut fruits are fungal rots, which cause major losses in fruit quality. The aims of this work were to determine the incidence, abundance and diversity of rots and fungi in three chestnut varieties (Longal, Judia and Martaínha) of Portugal, collected from an industrial plant, and to identify the stages of storage and processing where fungi and rots are more significant. Thirty-three chestnut samples from the three varieties were collected from different stages of industrial processing. Nuts were internally and externally inspected for damage, infestation and infection, and internal fungi were isolated and molecularly identified. The variety Martaínha was identified as the least susceptible to fungal growth, while Longal was the most susceptible. A high diversity of fungi was detected and identified. The dominant fungi were Mucor racemosus, Penicillium spp. (the causal agents of green rots), Ciboria batschiana (black rot) and Botrytis cinerea (gray rot). Gnomoniopsis smithogilvyi, the causal agent of brown rot, was also frequently detected. Sterilization with hydrothermal bath was effective in the elimination or reduction of most of the rot-causing fungi. These results could serve as a baseline for better monitoring fungal development and chestnut decay, and to develop effective management measures to control post-harvest chestnut rots.This work was funded by the project “ValorCast—Valorização da castanha e otimização da sua comercialização”, ref. PDR2020-101-032030, funded by Fundo Europeu Agrícola de Desenvolvimento Rural (FEADER) and the Portuguese government, under the scope of Ação 1.1 “Grupos Operacionais”, Medida 1. “Inovação”, PDR 2020—Programa de Desenvolvimento Rural do Continente. The Foundation for Science and Technology (FCT, Portugal) and FEDER under Program PT2020 provided financial support to CIMO (UID/AGR/00690/2020), SusTEC (LA/P/0007/2020), CITAB (UID/AGR/04033/2020) and Inov4Agro (LA/P/0126/2020).info:eu-repo/semantics/publishedVersio

Chestnut brown rot and Gnomoniopsis smithogilvyi: characterization of the disease and of the causal agent in Portugal

Sweet chestnut (Castanea sativa Mill.) is a nutritious food with high social and economic impact in Portugal. Fungal infection and rots lead to great economic and quality losses in stored chestnut. The fungus Gnomoniopsis smithogilvyi (syn. Gnomoniopsis castaneae) is currently considered one of the major threats to the chestnut chain worldwide. Considering the lack of knowledge on both the disease and the causal agent in Portugal, studies have been conducted in an attempt to timely develop the necessary control strategies towards the mitigation of the disease. Under this scope, the chestnut brown rot and its causal agent have been characterized for the first time in Portugal. The study was performed on chestnuts from Braganca, Portugal, that were received, processed and stored in a local industry during the growing season 2018-2019. Thirty-three samples were collected from different processing stages and from three chestnut varieties (Longal, Judia and Martaínha). Several isolates of G. smithogilvyi obtained were characterized at the morphological, ecophysiological, enzymatic and molecular levels. The fungus was also characterized in terms of pathogenicity and virulence. G. smithogilvyi was confirmed as the causal agent of brown rot disease in Portuguese chestnut varieties, which showed high susceptibility. The fungus showed high adaptability to chestnut substrates. The Portuguese isolates of G. smithogilvyi are morphologically and genetically similar to those isolated in other countries, even though some physiological and enzymatic variability was observed among the Portuguese isolates. Post-harvest control strategies towards the mitigation of the disease are discussed.This work was developed under the scope of “ValorCast – Valorização da castanha e otimização da sua comercialização” (PDR2020-1.0.1-FEADER-032034), funded by Fundo Europeu Agrícola de Desenvolvimento Rural (FEADER) and the Portuguese Government (Ação 1.1 Grupos Operacionais, Medida 1. Inovação, PDR 2020 – Programa de Desenvolvimento Rural do Continente). GP, JOD and PR are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020).info:eu-repo/semantics/publishedVersio