2.1. Plant material and pathogen inoculum.

Sterile PT2P line was harvested during their petiole extension period from an experimental tissue culture room at Zunyi Medical University in Guizhou province, China. First, P. carotovorum was cultivated with LB liquid medium to OD value of 0.6, which was measured at a wavelength of 600 nm. Then, PT2P line materials were inoculated with the same batch for research, set 0 h group and 20 h group, and set up a control group at the corresponding time point. The test group was co-cultivated by a PT2P line with 5 ml of P. carotovorum solution with an OD value of 0.6, and each group was repeated three times. The control group was co-cultured on the PT2P line with 5 ml of LB medium, and three repetitions were performed in each group. The co-cultivation conditions were maintained at 2000 Lx light intensity, 12 h/d illumination time and 25 ± 1°C of culture temperature.