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چکیده
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Grapevine-infecting viroids do not induce symptoms, except for Grapevine yellow speckle viroid-1 (GYSVd-1) and Grapevine yellow speckle viroid-2 (GYSVd-2), the agents of yellow speckle (YS), a disease characterized by yellow spots or flecks scattered on the leaf blade. The association of these viroids with Grapevine fanleaf virus (GFLV) is thought to elicit vein banding (VB), a syndrome characterized by chrome yellow flecks localized along the main veins and progressing into the interveinal areas of affected vines. The occurrence of these diseases and their causal agents was investigated in north-west Iran with a survey in which 137 vines were tested by multiplex RT-PCR for the presence of the five known grapevines viroids. GYSVd-1, GYSVd-2, Australian grapevine viroid (AGVd) and Hop stunt viroid (HSVd) were detected in 91%, 64%, 95%, and 100% of the tested samples, respectively, whereas Citrus exocortis viroid (CEVd) was not found. Combinations of three and four different viroids were present in most plants (88%) whereas GFLV was found in 50 samples (37%). The Iranian isolates of GYSVd-1, GYSVd-2, HSVd and AGVd showed minor molecular changes compared with the respective reference strains from grapevine. VB occurred in 22 vines infected by GYSVd-1, GYSVd-2 and GFLV, whereas YS symptoms, which occurred in 10% of the tested plants, were always shown by vines infected by GYSVd-1 and/or GYSVd-2. These findings are in line with the notion that assigns to GYSVd-1 and GYSVd-2 a role in the induction of YS and to both viroids and GFLV the genesis of VB.
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