Towards sustainable control of chestnut brown rot: An in vitro evaluation of conventional and biobased solutions.

Chestnut brown rot, caused by Gnomoniopsis smithogilvyi (syn. Gnomoniopsis castanea) (Gnomoniaceae, Diaporthales, Ascomycota), is a major threat to global chestnut production due to its latent infections and post-harvest symptom expression. This study investigated the role of temperature in pathogen biology and post-harvest disease development during storage. Mycelial growth and sporulation were optimal at 25 °C but, although reduced at extreme temperatures, they were not completely inhibited. Post-infection assays demonstrated that pathogen activation during storage is strongly influenced by the interaction between temperature and incubation period, underscoring the potential for disease progression under suboptimal storage conditions, even in asymptomatic chestnuts. The in vitro efficacy of synthetic fungicides, natural compounds, and biological control agents (BCAs) against G. smithogilvyi was also evaluated. Among the nine compounds tested, BIOCLEAN (whey, chitosan hydrochloride, and Equisetum arvense extract) and the Difenoconazole (SCORE) completely inhibited mycelial growth and sporulation. Boscalid + Pyraclostrobin (Signum) and Fosetyl-Al (Aliette) showed strong inhibition (>95 %), while moderate inhibition (78-85 %) was observed with Fluxapyroxad (Sercadis) and Fluopyram + Tebuconazole (Luna Experience). Potassium phosphonate and ionic copper formulations (Ocion ICC, Phozel) displayed limited efficacy. Among BCAs, Trichoderma simonsii exhibited the highest antagonism (72 % inhibition), followed by Bacillus amyloliquefaciens. Overall, the findings provide compelling evidence that rigorous temperature management during post-harvest storage, in combination with the application of targeted preharvest treatments in the field, can markedly reduce the incidence of brown rot. These results lay a solid foundation for the development of region-specific, integrated management strategies aimed at minimizing G. smithogilvyi-associated losses in commercial chestnut production.