First report of Hop stunt viroid from plum in China

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. It has since been found in a wide range of herbaceous and woody hosts, including cucumber, grapevine, citrus, plum, peach, pear, apricot, almond and pomegranate (Astruc et al., 1996). HSVd has been isolated from plums with dapple fruit disease in Japan (Sano et al., 1989), where the viroid occurs frequently. However, while plums originated in China and are extensively cultivated there, HSVd infection in this host in China has never been reported.

In September 2005, six plum varieties were collected from the Institute of Fruit Science in Changping district in Beijing, Peoples Republic of China. Total RNA was extracted (Li et al., 1995) from leaves and used for dot blot and reverse transcription-polymerase chain reaction (RT-PCR). Results of dot blot and RT-PCR showed that one of the six samples was positive for HSVd. The positive sample came from one of the most popular and widely grown varieties in China (‘Dashizaosheng’). There were no clear symptoms on leaves or bark when the samples were collected. A 297 bp DNA fragment was amplified from the sample by RT-PCR using primers R1 (5’-GCTGGATTCTGAGAAGAGTT-3’) for the RT reaction, followed by R2 (5’-AACCCGGGGCTCCTTTCTCA-3’) and F3 (5’-AACCCGGGGCA ACTCTTCTC-3’) for PCR, with both R2 and F3 primers including SmaI sites. The primers were complementary to residues 87-106 (R1), 67-84 (R2) and 79-96 (F3) of HSVd sequence Accession no. Y09349 respectively. Amplified products were cloned into pGEM-T (Promega, Madison, USA) and positive clones were selected by digestion with SmaI. Five clones were sequenced and two different sequences were obtained for those parts of the amplicons between the primers. Both were more than 99% identical to Acc. No. AB098501. One sequence (Acc. No. DQ648600) obtained from three clones had a single nucleotide change (G¹⁰⁷->A). The other one sequence (Acc. No. DQ648601) obtained from two clones had two nucleotide changes (C⁵⁹->T; G¹⁰⁷->A).

Many varieties of plum are grown in China. In further investigation HSVd was detected in a further 7 samples, of various varieties, out of 38 samples collected in China. To our knowledge, this is the first report of HSVd isolated from plum in China.