Bursaphelenchus xylophilus: An Important Pathogenic Factor of Pine Wilt Disease and Its Relationship with Bursaphelenchus mucronatus

Pine wilt disease is the most devastating pine disease caused by Bursaphelenchus xylophilus. Bursaphelenchus mucronatus is morphologically similar to B. xylophilus and geographically overlaps in its distribution. Although interspecific hybridization of the two nematodes has been performed in vitro, the dynamic regularity of hybrid formation and its risk in forests has not been well evaluated. In this study, a hybrid of B. xylophilus and Bursaphelenchus mucronatus mucronatus was identified in the laboratory and fields by molecular markers. The heterozygosity of ITS-5.8S loci for identification was unstable in the hybrid population, and the allele inherited from B. m. mucronatus was lost over several generations. We also provided evidence that hybrids existed in some new epidemic areas, while old epidemic areas were usually dominated by B. xylophilus. Hybrids could be generated when B. m. mucronatus was invaded by B. xylophilus, and the pathogenicity of the hybrids was similar to that of B. xylophilus. These findings may improve the understanding of the natural hybridization between B. xylophilus and B. m. mucronatus and pathogenic variation in pine wilt disease, providing new insights for future studies on disease detection, transmission, and quarantine.