گزارش ویروئید کوتولگی رازک (Hop stunt viroid) از درختان کامکوآت استان مازندران

Viroids are one of the most important pathogens in citrus, among which the pathogenic isolates of Hop stunt viroid (HSVd) cause Cachexia. In citrus, CVd-IIb and CVd-IIc variants of Hop stunt viroid differ from non-pathogenic variants in a six-nucleotide region with specific sequences in their variable region. During the visits of Kumquat (Citrus japonica) trees in the orchards of Mazandaran province, symptoms of gumming of the bark, stunting, yellowing of leaves, stem pitting and decline were observed. In this study, Biological indexing was performed in a greenhouse under controlled temperature (40˚C day and 28˚C night) using Etrog citron (C. medica) and Parson's Special mandarin (C. reticulata) both grafted on Rough lemon (C. jambhiri) and Citrang (Poncirus trifoliata × C. sinensis), respectively as common indicator plant for citrus viroids and specific indicator of Cachexia. The plants were inoculated with the inoculum from severe symptomatic trees of cachexia isolates from the origin of trees with signs of decline. After four months, RNA was extracted from the leaf vein and bark tissues of the shoots of the Etrog plants by SDS/Potassium acetate method. The expected fragments with a size of about 300 bp were obtained following reverse transcription polymerase chain reaction (RT-PCR) based on specific HSVd primers, and electrophoresis of products on 1% agarose gel. Sequencing analyzes showed the similarity of the studied isolates from declining trees with the pathogenic variants of HSVd. This is the first report of the occurrence of Hop stunt viroid as the cause of Cachexia in Kumquat trees in Mazandaran province.