Physiological markers of senescence in petunias. The fourth leaf from the top of 8‐week‐old plantlets was collected and painted with 30 μm dexamethasone (DEX) or 0.18% dimethylsulphoxide (DMSO) (v/v) in 0.6% agar medium. After 2 days, leaves were inoculated with two 10‐μL droplets using a spore suspension of Botrytis cinerea or mock solution. (a) The chlorophyll content in E9G plantlets infected with B. cinerea. Data represent two independent replicates [± standard error (SE), n = 10]. The chlorophyll content of detached leaves (b), malondialdehyde (MDA) level of detached leaves (c), catalase (CAT) level of detached leaves (d) and superoxide dismutase (SOD) level of detached leaves (e) at the indicated time points in vitro. Data represent three independent experiments (± SE, n = 120). Data were subjected to one‐way analysis of variance (ANOVA). Significant differences are indicated by letters (P < 0.05). 9XB, DEX treatment–B. cinerea inoculation on E9G; 9DB, DMSO treatment–B. cinerea inoculation on E9G; 7XB, DEX treatment–B. cinerea inoculation on E7H; 7DB, DMSO treatment–B. cinerea inoculation on E7H; 9XM, DEX treatment–mock inoculation on E9G; 9DM, DMSO treatment–mock inoculation on E9G; FW, fresh weight.