Cold Tolerance in Pinewood Nematode Bursaphelenchus xylophilus Promoted Multiple Invasion Events in Mid-Temperate Zone of China

Abstract

Pinewood nematode (Bursaphelenchus xylophilus) is a highly destructive invasive species, causing extensive economic and ecological losses across Eurasia. It has recently invaded mid-temperate zone of northern China, threating large areas of coniferous forests. Herein, we evaluated the physiological and molecular basis of cold tolerance in pinewood nematode isolates from different temperature zones of China. After exposure to −5 °C and −10 °C, the survival rates of five pinewood nematode isolates from different temperature zones were 93.94%–94.77% and 43.26%–45.58% after 8 h, and 93.04%–94.85% and 9.93%–10.56% after 24 h, without significant differences among isolates. In a comparison of an isolate from a mid-temperate zone and an isolate from a subtropical zone under gradient cooling, the survival rates remained steady at nearly 95% when minimum temperature ranged from −5 °C to −15 °C, with no significant difference between isolates. In addition, phylogenetic and population structure analyses based on whole genome resequencing data suggested that isolates from mid-temperate and warm temperate zones are clustered with different isolates from subtropical zone, with no obvious geographic pattern. We did not detect significant variation in cold tolerance ability and selected gene among pinewood nematode isolates from different temperature zones. The recently invaded pinewood nematodes in the mid-temperate zone of northern China may spread by multiple invasion events from southern China, without adaptive revolution. Our research implies that it is important to reinforce quarantine inspection to control the rapid spread of pinewood nematode.