First Report of Hop stunt viroid Infecting Japanese Plum, Cherry Plum, and Peach in Greece

Abstract

Dapple plum and peach fruit is a widely distributed disorder of plum and peach resulting in significant economic losses (4). During a survey for the presence of Hop stunt viroid (HSVd) on stone fruit trees in Greece, samples from 30 European plums (Prunus domestica L., cvs. President, Tuleu Grass), 45 Japanese plums (Prunus salicina Lindl., cvs. Angeleno, Diamond, Santa Rosa), 12 cherry plums (Prunus domestica L. var. insititia (L.) Fiori & Paoletti of unknown cultivar), and 107 peaches (Prunus persica (L.) Batsch, cvs. Red Haven, Elberta, June Gold, Spring Crest, Lemonato) were collected in several orchards around Greece. Their fruit skin symptomatology indicated viroid infection (reddish dappling blotches and cracks in European and Japanese plum, green dappling in cherry plum, and light colored blotches and lines in peach). Samples were screened with tissue-print hybridization (TPH) for HSVd using a full length DIG-labelled riboprobe deriving from in vitro transcription of the positive control, a citrus isolate of HSVd (G. Vidalakis, CCPP, University of California, Riverside). In total, 44 out of the 194 trees surveyed were HSVd-positive with TPH. For a small number (40) of TPH-positive field samples, TNA phenol extraction from fruit skin, leaves, and bark and one-tube two-step reverse transcription (RT)-PCR assays followed, using a standardized protocol (3) with two different primer pairs, one new primer pair (this study) and a previously reported primer pair (2). RT-PCR analysis showed the presence of HSVd in peach and Japanese plum in prefectures Pella (Central Macedonia), Achaia, and Korinthia (Peloponnesus) and in cherry plum in Achaia (Peloponnesus). Six of 11 Japanese plums (cvs. Angeleno, Santa Rosa), 2 of 12 cherry plums, and 8 of 12 peaches (cvs. Spring Crest, Red Haven) examined were found HSVd-infected, but none of the five European plums were. Nucleotide sequence analyses of purified and cloned amplicons from peaches and Japanese and cherry plums revealed sizes of 297 to 308 nt and similarity to sequence variants of other HSVd isolates previously characterized: 95 to 97% identity with the Moroccan isolates apr.9, apr.10, apr.11, and apr.12 and the Spanish isolate apr.4 from apricot (1) (GenBank Accession Nos. AJ297825 to AJ297828 and Y09346, respectively). For confirmation of HSVd presence in field trees, 10 Japanese plums cv. Angeleno, 10 peaches cv. June Gold, and 10 peaches cv. Spring Crest, HSVd-negative (TPH), were bud- or chip-grafted from two of the aforementioned Japanese plums cv. Angeleno and two of the aforementioned peaches cv. Red Haven. Two years later, five Japanese plum trees (cv. Angeleno) and five peach trees (three cv. Spring Crest and two cv. June Gold) were found HSVd-positive with TPH; no fruits were observed to produce fruit symptoms as the grafted trees were kept in an insect-proof greenhouse (no bees for cross-pollination). To our knowledge, our investigation reports for the first time the occurrence of HSVd infecting Japanese plum, cherry plum, and peach in Greece, emphasizing the need for a certification program for the prevention of spreading stone fruit tree viroids in this country. References: (1) K. Amari et al. J. Gen. Virol. 82:953, 2001. (2) N. Astruc et al. Eur. J. Plant Pathol. 102:837, 1996. (3). F. Faggioli et al. Acta. Hort. 550:59, 2001. (4) T. Sano et al. J. Gen. Virol. 70:1311, 1989.