Persistence of Phytoplasma and Control Efficacy of Oxytetracycline Tree Injection for Elaeocarpus sylvestris (Lour.) Poir. var. ellipticus (Thunb.) H.Hara Decline Disease

Elaeocarpus sylvestris (Lour.) Poir. var. ellipticus (Thunb.) H.Hara, an evergreen tree species native to Jeju Island, South Korea, has experienced a progressive decline associated with phytoplasma infection. This study aimed to evaluate the efficacy of oxytetracycline-based tree injection for suppressing phytoplasma and improving tree vitality. Two formulations—oxytetracycline hydrochloride (4.3%) and oxytetracycline calcium alkyltrimethyl ammonium (17%)—were administered to 40 infected individuals across two sites using a gravity-fed injection system. Treatment efficacy was evaluated based on chlorophyll content as an indicator of physiological recovery, while phytoplasma presence was assessed by PCR at 150 days after injection. The oxytetracycline hydrochloride group showed the highest suppression, with a 70% phytoplasma non-detection rate as determined by PCR analysis. Treated trees exhibited significantly higher chlorophyll content compared to untreated infected controls. These findings suggest that minimally invasive tree injection using oxytetracycline can provide temporary suppression of phytoplasma and support physiological recovery in E. sylvestris.