Study on the pathogenicity differences of two geographic populations of pine wood nematodes from North and South China on three larch species in Northeast China

The continuous expansion of Bursaphelenchus xylophilus (pine wood nematode) to the north and west poses a serious threat to the pine forest resources in Northeast China. Clarifying the pathogenicity of B. xylophilus to common larch tree species in this region is of great significance in effectively preventing the northward expansion of B. xylophilus.

Using manual inoculation, B. xylophilus strains collected from Fushun (Liaoning Province) and Changde (Hunan Province), were inoculated onto 3-year-old seedlings of Larix principis-rupprechtii, L. olgensis, and L. kaempferi. The pathogenicity of B. xylophilus to three types of larch along with the changes in physiological indicators such as water content, needle chlorophyll content, and defense enzyme activity were analyzed.

On the 30^th day, the incidence rate of L. principis-rupprechtii, L. olgensis and L. kaempferi inoculated with Changde strain were 100%, 100% and 86.7% respectively, and the disease index was 90, 85 and 82.1 respectively. The water contents of needle leaves were 11.46%, 35.35%, and 15.21%, respectively. The water contents of pine stems were 14.26%, 16.13%, and 15.82%, respectively. For the Fushun strain, the incidence rate of L. principis-rupprechtii, L. olgensis and L. kaempferi on the 30th day was all 100%, and the disease indeces were 100, 100 and 96.4 respectively. The water contents of needle leaves were 13.96%, 9.53%, and 9.25%, respectively. The water contents of pine stems were 11.53%, 12.2%, and 17.53%, respectively. The Fushun insect strain exhibited higher pathogenicity against these three types of larch. The effects of two populations of B. xylophilus on the chlorophyll content of three types of larch needles were similar, with L. principis-rupprechtii having the lowest chlorophyll content on the 30^th day after inoculation. In addition, defense enzyme activities such as APX, CAT, PAL, POD, and SOD showed significant changes and differences in the early stages of inoculation among the three types of larch, with greater fluctuations observed in response to the Fushun strain.

By inoculating two geographical populations of B. xylophilus onto three types of larch, it was found that the B. xylophilus strain from Fushun demonstrated stronger pathogenicity compared to the Changde strain. Among them, the L. kaempferi had a later onset of disease, while the L. principis-rupprechtii was more susceptible to B. xylophilus infection.