Biological characterization of citrus viroid VII

Area of Science:

• Plant Pathology
• Virology
• Horticultural Science

Background:

• Citrus viroid VII (CVd-VII) is an apscaviroid first identified in Australian lemon trees in 2015.
• Limited information exists on CVd-VII's biological characteristics and impact on citrus.

Purpose of the Study:

• To investigate the host range, transmission routes, and interactions of CVd-VII with other citrus viroids.
• To assess the potential threat of CVd-VII to citrus health and productivity.

Main Methods:

• Mechanical transmission experiments were conducted across various Citrus species and other plant families.
• Seed transmission was evaluated through detection in testa and embryo, followed by grow-out tests.
• Viroid detection in different plant tissues was performed to assess titres.
• Greenhouse trials were used to evaluate the effects of CVd-VII co-infection with other citrus viroids.

Main Results:

• CVd-VII successfully infected various Citrus species and varieties asymptomatically.
• Non-host species from different botanical families were identified.
• CVd-VII was detected in seed components but was not found to be seed-transmissible.
• Viroid titres varied significantly across different tissue types in infected plants.
• Co-infection with CVd-VII intensified symptoms, especially when combined with citrus dwarfing viroid and citrus exocortis viroid.

Conclusions:

• CVd-VII has a defined host range within Citrus but does not appear to be seed-borne.
• Accurate pathogen detection requires careful consideration of sample tissue type due to variable viroid titres.
• Co-infection with CVd-VII can significantly worsen disease severity, posing a threat to citrus production.