Pathogenicity of Gnomoniopsis smithogilvyi on four cultivars of sweet chestnut from Galicia (NW-Spain)

Gnomoniopsis smithogilvyi is an emergent pathogen that causes brown rot on nuts and burrs of sweet chestnut (Castanea sativa Mill.) in the main European producing countries, significantly reducing the production of this crop. In Galicia (northwestern Spain), this fungus was detected for the first time in 2021. In this region C. sativa is a species with high economic value, because it covers 66% of Spain’s plantations and produces 90% of the national nut production. The aim of this work was to evaluate the pathogenicity of two G. smithogilvyi strains on four cultivars of sweet chestnut from Galicia (‘Negral’, ‘Longal’, ‘Parede’ and ‘Xudía’). Nuts were surface disinfected and a superficial wound was made in the pericarp of each nut. A 5-mm mycelial agar plug of a 10-day-old culture of each G. smithogilvyi strain was inoculated. Ten nuts were treated for each strain and ten nuts inoculated with sterile PDA agar discs were used as a control. Tests were carried out twice. All of the nuts were kept in a moist chamber at 25°C. Two inoculated and two control nuts were inspected for the presence of rot symptoms every seven days. Three weeks after inoculation, the remaining nuts were examined and a disease severity index (DSI) establishing a scale of 0 to 4 was used to measure the damage. All the cultivars were affected by the pathogen with a range of disease of 0.8-2.7, while the controls remained healthy. Significant differences in severity between fungal strains of G. smithogilvyi were observed only for ‘Parede’. In all the inoculated nuts, the pathogen was re-isolated from symptomatic tissues and the identity was assessed by morphological and molecular analysis, confirming to be G. smithogilvyi.