Abstract: In this study, we investigated the effect of exogenous calcium and salicylic acid (SA) on Botrytis cinerea resistance in tomato seedlings. We treated a tomato strain susceptible to Botrytis cinerea with foliar spraying of water, SA, SA+CaCl₂ and SA+EGTA (Ca²⁺ chelating agent) for one to five days. During the treatment, leaves were collected to analyze the reactive oxygen species (ROS) content, phenylalanine ammonia lyase (PAL) activity, chintase and β-1,3-glucanase levels, and the expression of pathogenesis related protein 1, 2, 3 (PR1, PR2, PR3). Three days after infection, the disease index was
74.8 in control plants, and 46.9, 38.5 and 70.3 in SA, SA+Ca and SA+EGTA 〖JP〗treated plants, respectively. SA treatment significantly increased ROS leaf accumulation, and activities of PAL, chintase and β-1,3-glucanase. These values were further enhanced in SA+Ca treated plants, but decreased in SA+EGTA treated plants. Application of SA significantly increased the expression levels of PR1, PR2a and PR3b, which were further elevated by the combination treatment with Ca²⁺. These effects were counteracted by the combination treatment of SA and EGTA. The transcription levels of PR2b and PR3a were upregulated by 1-2 folds, and PR1, 2a and 3b by 2-5 folds in SA and SA+Catreated plants relative to control. These data suggested that application of Ca²⁺ could synergistically increase SAinduced resistance to B. cinerea. The resistance was associated with ROS accumulation, therefore the increase in resistance might be through ROS ability to increase the activity of defenserelated enzymes and expression levels of PR1, PR2a and PR3b.