The movement and distribution of citrus tristeza virus and citrus exocortis viroid in citrus seedlings1

The systemic movement of citrus tristeza virus (CTV) in sour orange (Citrus aurantium) seedlings and of citrus exocortis viroid (CEVd) in Etrog citron (C. medica) seedlings was studied. The movement of the two pathogens was analysed by detection in sections of roots and stems at different time intervals. Both pathogens were detected initially in the basal parts and the roots and subsequently spread to the shoot. CTV and CEVd moved in young citrus seedlings at similar rates. The findings are consistent with long distance phloem transport of the virus and the viroid. The practical implications of the pattern of systemic movement for diagnosis of infected trees are discussed.