Growth, physiological and biochemical responses of Pinus tabulaeformis to the infestation of Bursaphelenchus xylophilus

Pine wilt disease, a quarantine forest disease caused by Bursaphelenchus xylophilus, has brought huge threats to the forest ecosystems worldwide. The disease system is relatively complex, involving multiple factors such as nematodes, pine trees, and the environment. Its pathogenic mechanism and the disease-resistant mechanism of plants have not been fully elucidated yet. Pinus tabulaeformis is a key forest tree species with significant ecological importance. However, the physiological and biochemical response mechanisms of P. tabulaeformis to pine wilt disease are still not clear at present. Therefore, in this study, three-year-old potted seedlings of P. tabulaeformis were used as the research materials. For each treatment (control and nematode inoculation), a total of 9 potted seedlings with uniform growth were selected, with 3 pots for observing symptoms, 3 pots for measuring physiological and biochemical parameters, and 3 pots kept as spares. The growth, physiological, and biochemical parameters of the needles of P. tabulaeformis after inoculation with B. xylophilus were observed and measured. The results demonstrated that in comparison with the control group, nematode inoculation caused the content of chlorophyll a + b in the needles of P. tabulaeformis increased by 20.1 % at 1 day post inoculation (p > 0.05), but decreased by 4.8 % (p > 0.05), 24.1 % (p < 0.01), 52.9 % (p < 0.01), and 48.9 % (p < 0.001) at 3, 7, 15, and 30 days post inoculation (dpi), respectively. Meanwhile, nematode inoculation led to the withering and yellowing of some needles during the later stage of inoculation. Besides, nematode infestation causes a significant increase in electrolyte leakage (EL) by 12.9 % at 30 dpi (p < 0.01). Furthermore, the production rate of superoxide anion radicals (O₂^˙¯) increased by 55.3 % at 7 dpi (p < 0.01) under nematode infestation, followed by a 30.2 % significant reduction at 30 dpi (p < 0.05). Moreover, B. xylophilus inoculation resulted in a reduction in catalase (CAT) activity and total phenolic content while inducing a higher level of salicylic acid (SA) and jasmonic acid (JA) content and superoxide dismutase (SOD) activity. These findings demonstrate that nematode infestation causes certain harm to pine trees, but some disease-resistant substances within the pine trees will also be activated to resist the invasion of pine wood nematode. The results obtained from this research will lay a foundation for further understanding the disease resistance mechanism of pine wilt disease as well as its prevention and control.