Citrus is the most important fruit crop served as fresh fruit and for processing in the tropical and subtropical countries worldwide. Many different cultivars of citrus are cultivated in wide distribution in different areas from tropical, subtropical and temperate zones. Citrus systemic diseases of greening (HLB), and viruses such as citrus tristeza closterovirus (CTV), citrus tatter leaf cappilovirus (CTLV) and citrus exocortis viroid (CEVd), have been causing considerable damage to fruit yield and quality, and have become serious constraint for the citrus industry in the Asian and Pacific region in recent decades. This is due to their systemic invasion and common spread through infected budwoods, vegetatively propagated seedlings, and transmission by insect vector and by mechanical way. These systemic serious diseases are effectively controlled by integrated measures of disease management such as: 1) establishment of virus-free citrus cultivar repository, which is primarily important in preventing prevalence of the diseases; 2) precise and rapid disease indexing techniques indispensable for management of pathogen-free (PF) nursery system through health certificate of PF seedlings; 3) establishment of shoot-tip micrografting technique for obtaining PF germplasm foundation; and 4) performance of health management for preventing reinfection of PF trees in the field through IPM of vector insects.
The above-mentioned integrated techniques have been well-developed and performed for the improvement and development of the citrus industry in Taiwan. Also, Southeast Asian countries look forward to Taiwan’s technological support to prevent growers' losses due to the citrus greening and virus diseases. In recent decades, citrus greening disease (HLB) has been devastating citrus orchards in the Asian and Pacific region, and causing serious strain to the citrus industry in these areas. Basic information on the evolution of HLB strains in terms of pathogenicity and disease resistance is primarily important in formulating adequate measures for controlling the HLB disease.
For Year 2, the project shall have the following targets: