Progeny analysis of Iranian Citrus exocortis viroid isolate in two sensitive and tolerant rootstocks

Citrus exocortis viroid (CEVd) is the causal agent of exocortis disease, the economically important viroid disease of citrus. In this research, sequence polymorphism and population structure of CEVd were investigated in CEVd tolerant and sensitive hosts (sour orange (Citrus aurantium L.) and citrange (Poncirus trifoliata (L.) Raf. × C. sinensis (L.), respectively) seedlings. Full-length in vitro transcript of single sequence CEVd-S1 isolate was used for mechanical inoculation. The genetic diversity of CEVd populations was estimated in two citrus hosts by single-strand conformation polymorphism (SSCP) and sequencing. The analysis of cloned DNAs recovered from infected hosts by this isolate demonstrated that host species was effective on the variability within a single CEVd isolate. The amount and composition of the genetic diversity were different among the two hosts, and was higher in the tolerant host compared with the sensitive one. Furthermore, the analysis of thermodynamic secondary structures illustrated that nucleotide changes identified in this study did not induce major modifications in the viroid rod-like secondary structure.