‘ Candidatus Liberibacter asiaticus ’ is the causal agent of citrus huanglongbing, the most serious disease of citrus worldwide. We have developed and applied immunization and affinity screening methods to develop a primary library of recombinant single chain variable fragment (scFv) antibodies in an M13 vector, pKM19. The antibody population is enriched for antibodies that bind antigens of ‘ Ca. Liberibacter asiaticus’ . The primary library has more than 10 7 unique antibodies and the genes that encode them. We have screened this library for antibodies that bind to specifically-chosen proteins that are present on the surface of ‘ Ca. Liberibacter asiaticus ’. These proteins were used as targets for affinity-based selection of scFvs that bind to the major outer membrane protein, OmpA; the polysaccharide capsule protein KpsF; a protein component of the type IV pilus (CapF); and, two flagellar proteins FlhA and FlgI. These scFvs have been used in ELISA and dot blot assays against purified protein antigens and ‘ Ca. Liberibacter asiaticus ’ infected plant extracts. We have also recloned many of these scFvs into a plasmid expression vector designed for the production of scFvs. Screening of these scFvs was more efficient when phage-bound, rather than soluble scFvs, were used. We have demonstrated a technology to produce antibodies at will and against any protein target encoded by ‘ Ca. Liberibacter asiaticus ’. Applications could include advanced diagnostic methods for huanglongbing and the development of immune labeling reagents for in planta applications. [ABSTRACT FROM AUTHOR]