Viroids have been used as "graft transmissible dwarfing agents" (GTDA) in several countries, mainly to reduce growth of citrus trees, thus increasing their density in orchards. In the State of São Paulo, Brazil, plants of the acid lime 'Tahiti' are usually grafted with a complex of GTDA, presumably viroids. The aim of the present work was the identification and molecular characterization of the viroids infecting trees of acid lime 'Tahiti' displaying "Quebra galho" (bark-cracking). Viroids were identified and characterized by biological indexing in 'Etrog' citron, Northern-blot hybridization, RT-PCR, cloning and complete sequencing of the RNA genomes. Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd) and Citrus dwarfing viroid (CDVd) were found in different combinations. Although we have not been able to infer a direct relationship between the agronomical performance and symptom severity with the presence of a specific viroid or viroid combination, the differences in the severity of "Quebra-galho" symptoms among different trees is probably associated with the presence (or absence) of CEVd, with its interaction with other viroids perhaps determining the different phenotypes observed in the field.
Exocortis; Cachexia; Xyloporosis; Pospiviroidae; Pospiviroid; Citrus dwarfing
