Hop stunt viroid (HSVd) newly reported from hop in Xinjiang, China

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Xinjiang is the primary region of hop (Humulus lupulus) production in China due to high quality and productivity promoted by the favorable climate, geography and soil type. Hop stunt viroid (HSVd) was first described from hops with stunt disease in Japan (Yamamoto et al., 1970). HSVd belongs to the genus Hostuviroid, family Pospiviroidae, and has the broadest host range known for any viroid. The previous detection of HSVd in grapevine, peach, plum, apricot, citrus in China (Li et al., 2006; Yang et al., 2006; Zhou et al., 2006) led to the study of its distribution. In September 2007, one hundred hop leaf samples from Marco Polo, Qingdaodahua, Zhayi, Yulebite and Fenglu varieties (20 samples of each variety) were gathered from commercial hop fields in Changji districts of Xinjiang, China. Total RNA was extracted and subjected to dot blot hybridization using a digoxigenin-labelled HSVd cRNA probe (Li et al., 1995), and RT-PCR, with oligonucleotide primers HSVdR (5′-AACCCGGGGCTCCTTTCTCA-3′) and HSVdF (5′-AACCCGGGGCAACTCTTCTC-3′) specific for HSVd (Zhou et al., 2006). Dot blot hybridization results similar to that of HSVd reference control revealed the presence of HSVd in 23 samples including all 20 from Marco polo, 2 from Qingdaodahua and 1 from Zhayi. No hybridization signals were obtained for Yulebite and Fenglu varieties as for the healthy control. A 297-bp DNA fragment was amplified by RT-PCR from 3 samples of Marco Polo, then purified, cloned into pMD18-T vector (Takara) and sequenced. Eleven different clone sequences (Acc. No. EU365348–EU365353) had higher than 98% identities with that of the hop isolate (Acc. No. AB039271) reported in GenBank. Considering the high infection rate in Marco Polo variety and low infection rate in other hop varieties in the neighbouring field, future investigation will focus on elucidating whether the result is correlated with possible levels of tolerance/resistance. This is the first report of HSVd directly detected from hop in China. This study was supported by National Basic Research and Development Program (973) of China (No. 2006CB100203), the National Natural Science Foundation of China (30771403) and an Opening Project of The Key Oasis Eco-agriculture Laboratory of Xinjiang Production and Construction Group (200502).