Dear Editor,Citrus bacterial canker (CBC),one of the most destructive diseases of citrus,has a severe economic impact on citrus industries in tropical and subtropical countries (Das,2003).It has been widely known that Xanthomonas cirri subsp.cirri (Xcc) causes the CBC by transferring the type-Ⅲ effectors (T3SEs) to the interior of the plant cell through type-Ⅲ secretion system (T3S) to modulate transcription of host plants to trigger CBC disease (Schaad et al.,2006).Pathotype A,the Asiatic form of Xcc,has a wide host range,is pathogenic on almost all citrus varieties,and contains a major virulence gene pthA encoding a T3S-secreted transcriptional activator-like effector (TALE) that promotes cellular hypertrophy (Al-Saadi et al.,2007).However,the susceptibility gene in citrus being responsible for the CBC and matching PthA of Xcc is largely unknown.