Citrus canker, caused by a bacterial pathogen Xanthomonas
axonopodis pv. citri, is a widespread bacterial disease, which has
caused great economical loss in many citrus-producing countries
worldwide (Civerolo, 1984). The disease affects numerous
species including cultivars, and hybrids of citrus and citrus relatives.
There is no effective method available to deracinate citrus
canker, so it is still a severe worldwide quarantine disease.
Therefore, it is imperative to develop canker-resistant citrus cultivars.
However, conventional breeding aiming to improve canker
resistance has proved to be ineffective due to lack of diseaseresistant
germplasm (Brunings and Gabriel, 2003). Therefore,
genetic engineering offers an attractive and promising strategy
to protect susceptible commercial varieties against pathogens