PopW, a protein elicitor, reduces tomato bacterial spot disease caused by Xanthomonas euvesicatoria (X.e.) with a significantly decreased titer of X.e., achieving more than 50% biocontrol efficacy. Along with phenotype changes, apparent reactive oxygen species (ROS) burst and callose deposition were triggered by PopW at the cellular level; The mRNA abundance of PAMP-triggered immunity (PTI)-associated marker genes (PTI5, LRR22, GRAS2) was increased by PopW at the molecular level. These results demonstrated that PopW, as a PAMP, triggers early immunity of tomato against X.e. to reduce tomato bacterial spot disease. (C) 2015 Elsevier Inc. All rights reserved.