Synergistic antinematodal effects of fluopyram combined with chlorfenapyr and its potential mechanism against Bursaphelenchus xylophilus.

To enhance the chemical control of pine wilt disease (PWD) and mitigate resistance arising from the prolonged use of a single-agent pesticides, the nematicides fluopyram (FLU) and chlorfenapyr (CHL) were combined (FLU_CHL) to determine the optimal ratio and assess their effects on pine wood nematodes (PWNs) and the potential synergistic mechanisms. Results revealed that the optimal synergistic mass ratio of FLU to CHL was 1:3, with nematode survival rate, egg hatchability, and population size significantly lower than with FLU or CHL alone. At this ratio, FLU_CHL also induced morphological abnormalities in nematodes, such as body swelling, lip atrophy, and shrinkage of the male tail and female clitoral cover. Transcriptome sequencing data revealed that there were 313 (83 genes upregulated, 230 genes downregulated), 251 (74 genes upregulated, 177 genes downregulated), and 258 (112 genes upregulated, 146 genes downregulated) differentially expressed genes (DEGs) in FLU_CHL vs. control, FLU vs. control and CHL vs. control comparison groups, respectively. Comparative transcriptome analysis showed that Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways enriched in DEGs in the FLU_CHL vs. control comparison group encompassed those enriched for DEGs in the FLU vs. control and CHL vs. control comparison groups. Furthermore, RNA interference and FLU_CHL stress assays indicated that nematode mortality and reproduction rates were significantly reduced after silencing the BxSrab1 gene, a unique DEG in the FLU_CHL treatment group. This study provides a robust theoretical foundation for integrated pesticide applications in PWD control and offers insights for developing novel compound agents for disease management.