Bacterial pathogens of citrus: Citrus canker, citrus variegated chlorosis and Huanglongbing

Abstract Worldwide, there are literally hundreds of species of pathogens (fungal, bacterial, and viral) that attack citrus, yet there are only a very few that cause severe disease in epidemic proportions. Three bacterial genera contain species among these few are the subject of this chapter: (1) Xanthomonas species which requires no vector and causes hyperplastic cankers, with pathogen growth limited to intracellular mesophylic spaces of citrus leaves and stems; (2) Xylella fastidiosa subsp. pauca strains requires a vector and causes citrus variegated chlorosis (CVC), with pathogen growth limited to citrus xylem, and (3) Ca. Liberibacter species requires a vector and causes Huanglongbing (HLB), with blotchy mottling of leaves, much premature fruit drop, tree decline, and death, with pathogen growth limited to citrus phloem. Liberibacters are arguably the most destructive of all citrus pathogens, including viruses, viroids, oomycetes, bacteria, and fungi.