Characterization of viroids infecting grapevine in India

Abstract

Several viroids infect grapevine worldwide. They are smallest infectious pathogens. Present study was undertaken to detect viroids in commercial grapevine genotypes in India. Four viroids viz., Grapevine yellow speckle viroid-1 (GYSVd-1), Grapevine yellow speckle viroid-2 (GYSVd-2), Australian grapevine viroid (AGVd) and Hop stunt viroid (HSVd) were detected in reverse transcriptase-polymerase chain reaction (RT-PCR) based assay. These viroids were found to present either alone or in different combinations. None of the samples showed the presence of citrus exocortis viroid. Few genotypes like Beauty Seedless and Black Mustard did not showed the presence of any of the five viroids. Thompson Seedless, Sharad Seedless and Black Prince were found to be associated with all the four viroids. Blast analysis of Indian GYSVd-1 isolate revealed a close identity of 99% with Q4-III isolate from Pakistan, and Indian GYSVd-2 isolate was found to have close identity of 100% with VB-108 isolate from Croatia. While Indian HSVd isolate showed close identity of 99% with SDLY-20 isolate from China and AGVd Indian isolate was found to have close identity of 99% with AGVd-Iran isolate. GYSVd-2 association with grapevine was found for the very first time from the Indian conditions. Nucleotide substitutions, additions and deletions were observed in the sequenced isolates of these viroids. Variation was observed in the secondary structure of Indian Hop stunt viriod (HSVd) isolate. Characterization of all the detected viroids indicated that they might have been introduced in India from Asian or European countries.