Unveiling the nitro-oxidative dimension of copper toxicity in Phytophthora infestans

Copper (Cu) is an essential heavy metal widely used as a component of fungicides against pathogens, including Phytophthora infestans (Mont.) de Bary, the main cause of late blight disease. Despite the widespread use of Cu-based pesticides, data on their accumulation and long-term effects on economically important plant pathogens remain scarce. Therefore, this study assessed Cu-dependent alterations in nitro-oxidative homeostasis within P. infestans structures, as imbalances in reactive oxygen and nitrogen species (ROS/RNS) may disrupt pathogen development and host interaction. Biochemical and molecular methods were used to analyze two P. infestans genotypes with contrasting virulence toward potato cv. Bzura. Our results idicate that exposition of Avr/vr P. infestans to Cu stress reduced pathogen viability and increased the formation of ROS (superoxide radical anion, hydrogen peroxide) and RNS (nitric oxide, peroxynitrite, nitroxyl) within the pathogen structures. In the Avr genotype, Cu enhanced overall ROS production, whereas in the vr genotype only hydrogen peroxide was increased. Furthermore, Cu treatment induced genotype-specific nitro-oxidative DNA/RNA modifications: the Avr genotype showed elevated apurinic/apyrimidinic sites in DNA along with increased 8-OHG and 8-NG levels in RNA, while the vr genotype exhibited only higher 8-NG levels in DNA. To assess the impact of Cu exposure on P. infestans pathogenicity, disease index and molecular analyses of disease progression were conducted, revealing Cu-dependent acceleration of pathogen growth and host colonization. Overall, Cu-induced responses varied according to the pathogen's virulence profile, indicating distinct heavy-metal stress adaptation strategies among P. infestans genotypes and offering a potential explanation for the inconsistent effectiveness of Cu-based disease management strategies.