new hosts and comparison of biological and molecular characteristics of fig, mulberry, and citrus isolates of hop stunt viroid in iran

plant samples were collected from yazd, isfahan, fars and tehran provinces and examined for their possible infection by hop stunt viroid (hsvd). the experimental host range of the viroid was determined by injection of infected sap into greenhouse grown seedlings and subsequent assay of inoculated plants by rt-pcr. fig, mulberry and citrus isolates of the viroid were compared with respect to host range and molecular characteristics. among 120 samples collected from different regions and hosts, 13 samples from mulberry, fig, apple, quince, apricot, peach and citrus were infected with hsvd. the mulberry samples showed vein clearing and leaf deformation symptoms while usually no specific symptoms were observed in the fig samples. apple, quince, apricot, peach and citrus samples were also symptomless hosts. in greenhouse tests, mulberry isolate induced more severe symptoms. comparison of primary and secondary structures of the viroid isolates showed a closer similarity between the fig and mulberry isolates while the latter were less similar to citrus isolate. most differences of these isolates were in the pathogenicity, variable and terminal right regions which may determine the type and severity of symptoms