Primer sequences used in this study. from Enhancement of oxidative stress contributes to increased pathogenicity of the invasive pine wood nematode

Reactive oxygen species (ROS) play important roles in defence response of host plants versus pathogens. While generation and detoxification of ROS is well understood, how varied ability of different isolates of pathogens to overcome host ROS, or ROS contribution to a particular isolate's pathogenicity, remains largely unexplored. Here, we report that transcriptional regulation of ROS pathway, in combination with the insulin pathway, increases the pathogenicity of invasive species Bursaphelenchus xylophilus. The results showed a positive correlation between fecundity and pathogenicity of different nematode isolates. The virulent isolates from introduced populations in Japan, China and Europe had significantly higher fecundity than native avirulent isolates from the USA. Increased expression of Mn-SOD and reduced expression of catalase/GPX-5 and H2O2 accumulation during invasion are associated with virulent strains. Additional H2O2 could improve fecundity of B. xylophilus. Furthermore, depletion of Mn-SOD decreased fecundity and virulence of B. xylophilus, while insulin pathway is significantly affected. Thus, we propose that destructive pathogenicity of B. xylophilus to pines is partly due to upregulated fecundity modulated by insulin pathway in association with ROS pathway and further enhanced by H2O2 oxidative stress. These findings provide a better understanding of pathogenic mechanisms in plant–pathogen interactions and adaptive evolution of invasive species.This article is part of the theme issue ‘Biotic signalling sheds light on smart pest management’.