Viruses, greening bacterium and viroids associated with citrus (Citrus species) decline in India.
Three viruses, citrus tristeza closterovirus (CTV), citrus ringspot virus (CRSV) and citrus mosaic virus (CMV), the greening bacterium (GB), recently identified as Liberobacter asiaticum, and viroid infections were identified as the major pathogens associated with citrus decline in India. Information on characterization and development of diagnostic reagents for their rapid detection provide new avenues for their management. Variation in strains of pathogens and biotypes in the vectors was helpful in the management of vector-borne viruses through cross-protection. CRSV and CMV are newly discovered viruses and their incidence in Indian citrus was between 10 and 70%. Both viruses were transmitted through buds and hence can be effectively managed by bud selection. The monoclonal antibodies developed for CTV and GB have been used for pathogen-specific detection in ELISA. However, CMBV and GB were also detected by nucleic acid probes in DNA-DNA hybridization, whereas CRSV was detected only by serological methods and viroids by PAGE and specific nucleic acid probes. It is suggested that these methods will be of use in the development of sound indexing programmes for budwood certification.