Early Diagnosis of Pine Wood Nematode Disease Based on Chlorophyll Fluorescence Parameters and Organic Acids

Pine wood nematode disease is a destructive disease to the ecological environment and forest resources. The disease is produced by Bursaphelenchus xylophilus, and the onset rate is extremely fast and the pathogenesis of the disease is not clear. Prevention of this disease is still important in production, so it is of great significance to explore its early diagnosis. In this study, the changes of chlorophyll fluorescence dynamic induction parameters, non-photochemical quenching parameters and organic acid content in needles of 7-year-old-infected Pinus hwangshanensis were studied by chlorophyll fluorescence technology and organic acid mass combined technology. The results showed that in the chlorophyll fluorescence dynamic induction group, Fm/Fo, Fv/Fo, Fm, Psi_o and Pi_Abs showed a significant downward trend, while Phi_Do, ABS/RC, TRO/RC and DIO/RC showed a significant uptrend. In non-photochemical quenching, Fm showed a downward trend, while Qp_L1, Qp_L2, QY_L1, QY_L2 and QY_Lss showed a significant upward trend. In the change of organic acid content, ferulic acid, syringic acid, gallic acid and jasmonic acid showed a significant increasing trend, while benzoic acid and salicylic acid showed a first increasing trend and then decreasing trend. Experimental results show that pine wood nematode had significant effects on photosynthesis and the organic acid content of pine before it showed symptoms of the disease. After comprehensive analysis, chlorophyll fluorescence dynamic induction parameters Pi_Abs, Fm, Phi_Do, TRO/RC, Psi_o, non-photochemical quenching parameters QY_L2, Qp_L1, QY_Lss, QY_L1 and organic acids ferulic acid, syringic acid, benzoic acid and gallic acid contents are ideal indicators for early diagnosis of pine wood nematodiasis.