Resistance genes mediate differential resistance to pine defensive substances α-Pinene and H2O2 in Bursaphelenchus xylophilus with different levels of virulence

The pine wood nematode (PWN), Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, is the pathogen of pine wilt disease (PWD) which can devastate forests. PWN can be of high or low severity and the mechanisms underlying the differences in virulence are unclear. Therefore, it is necessary to study the relationship between differentiation of PWN severity and its resistance to the main defensive substances of pine species (i.e., α-pinene and H2O2). The feeding rate and fecundity of PWN was examined at different levels of virulence under conditions of α-pinene and H2O2 stress. Moreover, the expression patterns of the main resistance genes of PWN with different virulence were determined under conditions of α-pinene and H2O2 stress. The feeding rate and fecundity of the high virulence strain AMA3 were higher than those of the low virulence strain YW4. The expression levels of the autophagy gene BxATG5, cytochrome P450 gene BxCYP33D3, and glutathione S-transferase genes BxGST1 and BxGST3 in AMA3 increased significantly upon exposure to α-pinene for 2 h, while these genes showed smaller degrees of upregulation in YW4. Under conditions of H2O2 stress, the expression levels of BxATG5, catalase genes Bxy-ctl-1and Bxy-ctl-2, and the 2-cysteine peroxiredoxin gene BxPrx in AMA3 were higher than those in YW4. These findings suggest that high virulence PWN has greater resistance to pine defensive substances α-pinene and H2O2 than low virulence PWN, and resistance genes mediate the differential resistance of PWN strains. This study will contribute to the clarification of the mechanism underlying virulence differentiation of PWN and will advance understanding of the pathogenic mechanism of PWD.