| The continuous expansion of B. xylophilus 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 Northeast China is of great significance in effectively preventing the northward expansion of B. xylophilus. Using manual inoculation, B. xylophilus strains collected from Fushun, Liaoning and Changde, Hunan 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 and the changes in physiological indicators such as water content, needle chlorophyll content, and defense enzyme activity were analyzed. On the 30th 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 moisture content of needle leaves is 11.46%, 35.35%, and 15.21%, respectively; The moisture content of pine stems is 14.26%, 16.13%, and 15.82%, respectively. The incidence rate of L.principis rupprechtii, L. olgensis and L. kaempferi inoculated with Fushun worm strain on the 30th day was 100%, and the disease index was 100, 100 and 96.4 respectively; The moisture content of needle leaves is 13.96%, 9.53%, and 9.25%, respectively; The moisture content of pine stems is 11.53%, 12.2%, and 17.53%, respectively. The Fushun insect strain has high 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 30th 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. Among them, after inoculation with the Fushun B. xylophilus strain, the defense enzyme activities of the three types of larch showed significant differences. By inoculating two geographical populations of B. xylophilus onto three types of larch, it was found that the B. xylophilus strain from Fushun has 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. |
