Evaluation of Inhibitory Effect and Mechanism of Euphorbia Factor L3 against Phytophthora capsici

Phytophthora capsiciis a highly destructive phytopathogenic oomycete with a broad host range and is responsible for tremendous losses. Euphorbia factor L3(EFL3) is a natural plant-derived compound that has been widely studied in medicine and cosmetic applications. In this study, the sensitivity of 105P. capsiciisolates to EFL3was determined, and the biological activity and physiological effects of EFL3againstP. capsiciwere investigated. The median effective concentration (EC50) values for EFL3inhibition mycelial growth and spore germination ranged from 0.66 to 8.94 μg/mL (mean, 2.96 ± 0.91 μg/mL) and 1.63 to 13.16 μg/mL (mean, 5.30 ± 1.64 μg/mL), respectively. EFL3treatment resulted in cell wall and cell membrane damage ofP. capsici, which was revealed by morphological and ultrastructural observations, propidium iodide (PI) and calcofluor white (CFW) staining, and measurements of relative conductivity as well as malondialdehyde (MDA) and glycerol contents. In addition, the contents of phospholipid and cellulose, which are the major components of cell membrane and cell wall, were significantly reduced following EFL3treatment. Furthermore, EFL3provided protective as well as curative efficacies againstP. capsicion detached tomato leaves and pepper seedlings in vivo. These data show that EFL3exhibits strong inhibitory activity againstP. capsici, thereby suggesting that it could be an effective alternative for controllingP. capsici-induced diseases.Keywords:baseline sensitivity;botanical fungicide;Euphorbia factor L3;action mechanism;Phytophthora capsici