First Report of Hop stunt viroid in Apricot in China.

Abstract

Hop stunt viroid (HSVd), a member of the family Pospiviroidae, was first described as the causal agent of hop stunt disease in Japan. It has since been found in a wide range of hosts including herbaceous and woody hosts (e.g., hop, cucumber, grapevine, citrus, plum, peach, pear, apricot, almond, and pomegranate). It was also detected and characterized in apricot where infection appears to be latent (1). The viroid occurs frequently in apricot. In southeastern Spain, the presence of HSVd was found to infect 81% of apricot trees (2). Apricots originated in China and are extensively cultivated, but HSVd infection in this host has not been reported. In September 2005, a single symptomatic apricot tree, 'Yin Bai', one of the most popular and widely grown cultivars in China, was discovered at the Institute of Fruit Science in Changping District in Beijing, Peoples Republic of China. Observed symptoms included a number of yellow spots with an irregular border that scattered in an irregular manner over the leaf surface. Total RNA was extracted and used for return-polyacrylamide gel electrophoresis and reverse transcription-polymerase chain reaction (RT-PCR) (4). Results of both assays were positive for HSVd. A 297-bp full-length DNA fragment was amplified by RT-PCR using primers R1 (5'-GCTGGATTCTGAGAAGAGTT-3') complementary to HSVd residues 87-106 for the RT reaction, followed by R2 (5'-AACCCGGGGCTCCTTTCTCA-3') complementary to HSVd residues 67-84 and forward primer F3 (5'-AACCCGGGGCAACTCTTCTC-3') residues 79-96 for PCR. The primers are located in the strictly conserved central region of the conserved HSVd group and contain the unique endonuclease restriction site SmaI. The amplified products were cloned into pGEM-T (Promega, Madison, WI) and selected for further analysis on the basis of the results of restriction digests. Six individual clones were sequenced and three different sequences were obtained. Nucleic acid sequence (GenBank Accession No. DQ362901) obtained from one clone was 99.3% (nucleotide changes T206→C, C233→T) identical to HSVd.apr8 (GenBank Accession No. Y09349) (3). Sequence (GenBank Accession No. DQ362904) obtained from three clones was 99.7% (nucleotide change C233→T) and a third sequence (GenBank Accession No. DQ362905) obtained from two clones was 99.3% (nucleotide changes G107→A, C233→T) identical to HSVd.apr8. Further investigation is necessary to determine whether the symptoms observed are associated with the viroid infection. To our knowledge, this is the first report of HSVd isolated from apricot in China.