Viroid Prevalence in Tunisian Citrus.

Area of Science:

• Plant Pathology
• Horticulture
• Virology

Background:

• The Tunisian citrus industry relies on local cultivars, with sour orange as the primary rootstock.
• Tristeza disease poses a significant threat to Tunisian citrus production.
• Viroid sensitivity in promising rootstocks necessitates an assessment of current citrus cultivar infection status.

Purpose of the Study:

• To survey symptomless citrus cultivars in Tunisia for viroid infections.
• To identify specific viroids and their combinations present in Tunisian citrus.
• To inform the selection of alternative rootstocks for tristeza-tolerant citrus production.

Main Methods:

• Graft-inoculation of Etrog citron with tissue from 174 symptomless citrus sources.
• Observation of viroid infection symptoms in indicator plants.
• Analysis using sequential polyacrylamide gel electrophoresis and molecular hybridization with viroid-specific probes.

Main Results:

• All surveyed citrus sources were infected with at least two viroids.
• Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd), and Citrus viroid III (CVd-III) were highly prevalent.
• CEVd+HSVd+CVd-III and CEVd+CVd-III were the most frequent viroid combinations found.

Conclusions:

• Widespread viroid infection in Tunisian citrus cultivars presents a challenge for developing tristeza-tolerant rootstock/scion combinations.
• The high prevalence of CEVd, HSVd, and CVd-III indicates a need for careful rootstock selection.
• Further research is required to identify and implement alternative rootstocks resistant to both tristeza and prevalent viroids.