Effects of Bursaphelenchus xylophilus Infestation on Physiological Indexes of Larix kaempferi

The dynamic changes of photosynthetic pigment content, osmotic regulatory substances, phenylalanine ammonia lyase and antioxidant enzyme system were determined to explore the response of Larix kaempferi to the infection of Bursaphelenchus xylophilus from the physiological and biochemical perspectives. Three-year-old potted L. kaempferi was used as the experimental material. Two thousand B. xylophilus were inoculated by artificial skin grafting method. The chlorophyll content, soluble protein content, antioxidant enzymes(superoxide dismutase SOD, catalase CAT and peroxidase POD) activities and phenylalanine ammonia lyase(PAL) activities were collected and measured on the 0, 5, 10, 20, and 30 days after inoculation. The results showed that a large number of B. xylophilus were detected in the upper and lower parts of the inoculated site of L. kaempferi, and the number of nematodes in the lower part was significantly higher than that in the upper part(P<0.01). The contents of chlorophyll a and b both decreased significantly on the 10^th day, and then began to increase, which had no significant difference with the control group. After 10 days of inoculation, the content of soluble protein gradually increased and was significantly higher than that of the control group(P<0.05). The SOD activity increased significantly after B. xylophilus inoculation, which was significantly higher than that of the control group at each time point(P<0.01). CAT activity decreased slightly at first and then increased gradually, which was significantly higher than that in the control group at 30 days(P<0.01). POD activity decreased first and then increased, and increased rapidly after 5 days, which was significantly higher than that of the control group at each time point(P<0.05). The activity of PAL increased at first and then decreased. The activity at 10 and 20 days after inoculation was significantly higher than that in the control group(P<0.05). The changes of chlorophyll content, soluble protein content, antioxidant enzymes and PAL activities were closely related to the disease resistance of L. kaempferi infected with B. xylophilus. The results of this study can provide a reference for the screening of resistance lines and the resistance mechanism of L. kaempferi infected with B. xylophilus.