Abstract: [Objective] This study was to observe the trends of chemical signals when the different resistant individuals of Pinus massoniana had been inoculated with pine wood nematodes, in order to provide the theoretic support for clarifying the resistant mechanism of infected trees of P. massoniana.[Method] The high resistant and susceptible clones had been selected following a serious of breeding produce. The dynamic variation of signal moleculars including H₂O₂, O₂^-·, NO and Ca²⁺ was detected in needles of different resistant clones at 1, 3, 7, 15 and 30 d post inoculation (dpi).[Result] The results showed that a large number of pine wood nematodes were detected in different parts of susceptible clones, while no nematodes were found in the high resistant clones. The H₂O₂ content significantly increased in different resistant clones at 1, 3 and 7 dpi. The H₂O₂ content in high resistant ones was returned to the health level after 15 dpi but the susceptible ones rose sustainably. As a result, the H₂O₂ content in susceptible clones was 1.77 times higher than that in resistant ones. The O₂^-· content also significantly increased in both resistant and susceptible clones during 1 to 15 dpi. They had a same trends and no significantly differences. The high resistant clones reduced the O₂^-· content at 30 dpi but the susceptible ones still increased it. There was no significant difference in NO content between high resistant clones and the control group during 1 to 15 dpi. It was significantly higher than control group at 30 dpi. However, the NO content in susceptible ones was significantly higher than that of the control group and high resistant ones at each time point. The variation trend of Ca²⁺ content was similar between different resistant clones post inoculation. They both performed in an up-down-up-down trend. The Ca²⁺ content of high resistant clones was significantly higher than that of control group and susceptible ones at 1 dpi and 15 dpi. However, the Ca²⁺ content of high resistant clones maintained at an ordinary level at the other time points. The Ca²⁺ content of susceptible clones was significantly higher than that of control group at each point.[Conclusion] The content of H₂O₂, O₂^-· and Ca²⁺ would increase rapidly when the pines were invaded by nematode. They could induce defensive response as signal moleculars. The high resistant clones had an effective way to control signal molecular content and finally returned to normal physiological metabolism. However, the susceptible ones could not control and the excessive ROS and Ca²⁺ would damage the plants. NO content was stable in the high resistant clones post inoculation. But it was accumulated at each time point in susceptible ones. The redundant NO is harmful for P. massoniana metabolism.

Key words: Pinus massoniana, pine wood nematode, resistant, susceptible, signal molecular