Bacterial canker diseases in tomato and pepper are caused by Clavibacter michiganensis subsp. michiganensis and C. michiganensis subsp. capsici, which are Gram-positive plant-pathogenic bacteria (Figure 1). Although several virulence factors such as serine proteases and cellulase have been determined in these pathogens, pathogenesis mechanisms have not been well understood. Thus, we are trying to find critical virulence factors using diverse genomic analyses (Figure 2) and also to determine how these pathogens infect the host plants, tomato or pepper. Bacterial canker in kiwifruit is very severe in most of kiwifruit-cultivating countries, including Korea, and is caused by Pseudomonas syringae pv. actinidiae, a Gram-negative plant-pathogenic bacterium. The fire blight is also very problematic worldwide and this disease was observed in Korea since 2015. To manage these diseases, antibiotics-based chemicals are somewhat effective. However, antibiotics-resistant bacterial strains have been emerged and also in many countries, including European countries and New Zealand, the use of antibiotics is prohibited. Therefore, to find alternative methods for managing these diseases are very urgent. Bacteriophages are the viruses killing only target host bacteria very specifically (Figure 3) and recently phage therapy using bacteriophages have been reconsidered as a biological control for bacterial diseases. We are trying to develop phage therapy to manage these bacterial canker and fire blight diseases in kiwifruit and apple and pear trees. Fire blight disease caused by Erwinia amylovora was reported in Korea in 2015 (Figure 4). In addition, bacterial black shoot blight disease is very similar to fire blight disease in apple and pear. This disease was first reported in Korea and is caused by Erwinia pyrifoliae, a Gram-negative plant-pathogenic bacterium. Nationwide extensive eradication programs have been operated in Korea for these diseases. However, ecology of these diseases or pathogens has not been well studied. Now, we are trying to monitor these diseases in apple and pear orchards in Korea. First, bacterial wilt disease in tomato is caused by Ralstonia solanacearum, which is a Gram-negative plant-pathogenic bacterium. This pathogen can survive in soil for a long time. Once the host plant, tomato, is planted, a pathogen infects the plant through roots and it enters into xylem tissue eventually. Then, bacterial pathogens multiply and block water movement mostly by exopolysaccharides (EPS). Second, bacterial canker disease in tomato is caused by Clavibacter michiganensis subsp. michiganensis, which is a Gram-positive plant-pathogenic bacterium. This bacterium also infects xylem tissue and is transmitted by seeds. So far, not much tomato genetic resources to carry disease resistance against each disease have been reported. We are collecting tomato genetic resources to carry disease resistance against each disease and are aiming to study genetic factors to determine disease resistance to bacterial wilt or bacterial canker disease in tomato, using collected genetic resources. Plants have molecular mechanisms to recognize and trigger disease resistance to diverse pathogens. In particular, bacterial plant pathogens carry two different types of elicitors: PAMPs (pathogen-associated molecular patterns) such as flagellin and peptidoglycan and effector proteins. Effector proteins are proteins that are secreted from pathogens and delivered into plant cytoplasm. Mostly, they act as virulence factors. Certain plant cultivars have resistance (R) proteins to recognize corresponding effector proteins and trigger effector-triggered immunity (ETI). Once ETI is triggered, the hypersensitive response (HR), which is a localized and rapid cell death at the infection sites, is followed. Although Clavibacter michiganensis subsp. michiganensis does not carry typical effectors, it can induce HR in Nicotiana benthamiana. We are examining pathogen factors carrying HR-eliciting activity and also their mechanisms to cause HR in this plant.