Application of Iron Chlorine E6 alleviate on growth defect of Cunninghamia lanceolata caused by Colletotrichum gloeosporioides

: To investigate the alleviation effect of a novel plant growth regulator, 0.02% iron chlorin e6 (ICE6) water-soluble powder, on Cunninghamia lanceolata growth under stress caused by Colletotrichum gloeosporioides, this study used C. gloeosporioides as the test pathogen and 2-year-old C. lanceolata seedlings from Yangkou Forest Farm, Fujian Province as experimental materials. Seedlings were treated with iron chlorin e6 solutions at different concentrations (0.01, 0.02, 0.04, and 0.08 μg·mL⁻¹), and each treatment group was sprayed with a C. gloeosporioides spore suspension (5 × 10⁶ spores·mL⁻¹). The impacts of different concentrations of 0.02% ICE6 on induced resistance in C. lanceolata, malondialdehyde (MDA) content in leaves, and the activity of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were measured.Results showed that: (1) Plate antibacterial assays indicated no significant differences in the inhibition rates of C. gloeosporioides among different concentrations of ICE6. (2) Under C. gloeosporioides stress, spraying 0.08 μg·mL⁻¹ iron chlorin e6 solution significantly enhanced C. lanceolata resistance to C. gloeosporioides. (3) Biofilm damage assessments revealed that after spraying iron chlorin e6 solutions at various concentrations and subsequent inoculation with C. gloeosporioides, MDA content in plant leaves was significantly lower than in the control group, with the 0.08 μg·mL⁻¹ treatment group exhibiting the lowest degree of membrane lipid peroxidation damage. (4) Antioxidant enzyme activity assays demonstrated that spraying 0.08 μg·mL⁻¹ iron chlorin e6 significantly increased SOD, POD, and CAT activities in C. lanceolata leaves. (5) Scanning electron microscopy (SEM) observation of leaf ultrastructure showed that treatment group leaves were smoother than control leaves, with no hyphal invasion observed in mesophyll tissues. In summary, application of 0.02% ICE6 water-soluble powder at various concentrations alleviated the occurrence of C. lanceolata anthracnose. Prolonged treatment activated the host’s systemic defense responses and enhanced seedling resistance to C. gloeosporioides. Among these, plants sprayed with 0.08 μg·mL⁻¹ iron chlorin e6 solution exhibited the mildest disease severity, the least damage to the cell membrane system, and the strongest activity of the antioxidant enzyme system after pathogen inoculation.