Occurrence of Gnomoniopsis smithogilvyi in Chestnut Under Different Management Systems in Northeastern Portugal

Chestnut brown rot caused by Gnomoniopsis smithogilvyi represents an increasing threat to Castanea sativa production, although its endophytic behaviour and response to pre-harvest management strategies under field conditions remain poorly understood. This study evaluated the occurrence of G. smithogilvyi in different chestnut tissues and assessed the effects of targeted field treatments on pathogen colonisation and fruit quality in commercial orchards located in north-eastern Portugal. Field trials included applications of a biological fungicide (Problad®), an inorganic micronutrient fertilizer (Fungicrops Bio®), a sulfur-micronutrient fertilizer (KSC Mix®), and a potassium-phosphonate chemical fungicide (Fosetyl-Al®), alongside untreated control orchards. Samples of leaves, branches, burrs, and nuts were subjected to microbiological and molecular analyses, while fruit external quality parameters were also assessed. G. smithogilvyi was detected in all analysed organs, confirming its widespread endophytic occurrence. Treatment effects were more pronounced in reproductive tissues, with Problad® and Fosetyl-Al® significantly reducing pathogen incidence in burrs and nuts compared with the control. KSC Mix® promoted fruit development but did not significantly reduce fungal incidence. Treated orchards generally showed improved fruit quality and lower insect infestation. Phylogenetic analysis confirmed the identity of all isolates as G. smithogilvyi. Overall, the results highlight the complexity of managing chestnut brown rot and support the need for integrated and sustainable disease management strategies.