Assessing Gnomoniopsis castanea spores in two chestnut groves of Trás-os-Montes by air sampling and evaluating the application of cupric fungicides on leaves and burrs to reduce disease inoculum

Abstract

Gnomoniopsis castanea is an emerging pathogen of Castanea species, causing nut rot, bark cankers, and leaf necrosis, while also existing asymptomatically as an endophyte. This study evaluated the presence of G. castanea spores in two chestnut orchards in Trás-os-Montes (Sobreiró, Vinhais) and assessed the effect of copper-based fungicides in reducing inoculum levels in leaves and burrs. Air samples were collected weekly from May to October 2024 at two heights per tree using a SAS air sampler. Colonies identified as G. castanea were isolated and cultured for confirmation. Additionally, symptomatic leaves and burrs were treated with Nordox copper (1 g/L) and incubated in outdoor cages at Instituto Politécnico de Bragança. Air sampling from these cages was conducted between March and June to detect remaining spores. In vitro sensitivity tests were performed using copper sulphate and Copper Nordox at varying concentrations. Airborne spores were detected in both orchards, and a total of 50 G. castanea isolates were obtained, confirming species identity via molecular analysis. The in vitro trials showed increasing inhibition with higher copper concentrations. Copper Nordox was more effective, achieving up to 54.29% inhibition, compared to a maximum of 17.46% with copper sulphate, indicating its potential to reduce disease inoculum in chestnut orchards.