Physiological and Biochemical Responses of Idesia polycarpa to Botryosphaeria dothidea Infection at Different Stages of Stem Canker Disease

Botryosphaeria dothidea (Moug. ex Fr.) Ces. & De Not. is a major pathogenic fungus causing stem canker in Idesia polycarpa, posing a significant threat to the growth and survival of its plantations. To elucidate the physiological and biochemical responses of the host under pathogenic stress, this study used two-year-old potted seedlings of I. polycarpa (provenance: ‘Emeishan No. 1’) and conducted artificial inoculation. Dynamic changes in physiological and biochemical indices at different disease stages were systematically monitored. The results revealed a distinct stage-specific response pattern: in the early infection stage, the activities of antioxidant enzymes (POD and SOD) increased rapidly, accompanied by significant elevations in osmotic regulators such as proline and soluble protein. In the mid-stage, malondialdehyde (MDA) content increased, while the levels of photosynthetic pigments—especially chlorophyll b and carotenoids—declined, indicating intensified oxidative damage. In the late stage, antioxidant capacity and osmotic adjustment weakened, and the photosynthetic system was continuously impaired. Correlation analysis further demonstrated significant synergistic relationships among antioxidant defense, membrane stability, osmotic regulation, and photosynthetic function. These findings enhance our understanding of the disease resistance mechanisms in I. polycarpa and provide a theoretical and practical reference for resistance evaluation and precise management of canker disease in woody species.