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First Report of Onion yellow dwarf virus in Leek (Allium ampeloprasum var. porrum) in Spain

Fernández-Tabanera, E., Fraile, A., Lunello, P., García-Arenal, F., Ayllón, M. A.
Plant disease 2018 v.102 no.1 pp. 256
Allium porrum, Iris yellow spot virus, Leek yellow stripe virus, Onion yellow dwarf virus, RNA, Shallot latent virus, alternative hosts, amino acid sequences, coat proteins, crop losses, crops, flowers, garlic, gels, greenhouses, leaves, leeks, mixed infection, nucleotide sequences, onions, reverse transcriptase polymerase chain reaction, roots, seed quality, seeds, spring, stems, viruses, Iran, Spain
Leek (Allium ampeloprasum var. porrum) is one of the most important culinary plants in the world. Spain is the sixth European producer and the crop makes a considerable fraction of the total area of vegetable production (MAPAMA 2016). Leek is often affected by different viruses such as Iris yellow spot virus, Leek yellow stripe virus, and Shallot latent virus (Katis et al. 2012). Onion yellow dwarf virus (OYDV, genus Potyvirus) is one of the most widespread viruses in garlic and onion and affects the development and quality of the crops (Katis et al. 2012). OYDV causes mosaic and yellow streak striping in garlic leaves and in onion causes stem distortion, reduced number of flowers and seeds, and a loss of seed quality (Conci et al. 2003; Katis et al. 2012). However, OYDV has been found in leek only in Iran (Naderi Saffar et al. 2013), and had not been reported in leek in Spain. The aim of this study was to analyze the presence of this virus in leek crops from the northern half of Spain. In spring of 2015, 30 leek plants of four different varieties (Curling, Custeau, Megaton, and Pluston), showing symptoms of inverted roots and cracked stems, were collected from fields near San Pablo de la Moraleja, Valladolid (Castilla y León, Spain). Total RNA was extracted from 100 mg of leaf tissue of the 30 symptomatic field plants and healthy greenhouse plants (negative control) with the RNeasy Plant Mini kit (Qiagen, Germany) according to the manufacturer’s instructions. An RNA-DIG labeled probe, designed for the detection of a partial sequence of OYDV coat protein sequence (Ayllón et al. 2012), was used in a dot-blot assay. Nine out of the 30 analyzed symptomatic leek plants (30%) tested positive, while negative controls remained negative. To confirm the presence of OYDV, a two-step RT-PCR was performed using the same specific primers designed to amplify the region corresponding to the RNA probe (Ayllón et al. 2012). Amplicons of the expected size (234 bp) were obtained from the nine dot-blot positive samples and from another four plants; in total, 13 out of the 30 analyzed plants tested positive. OYDV was detected in leeks of all varieties analyzed. The presence of OYDV was not apparently related to the symptomatology observed in the leeks since it was not detected in all symptomatic samples, and no specific symptomatology of OYDV was observed in these plants. All RT-PCR products were purified with the gel extraction kit (Agilent) and their nucleotide sequence determined in both directions. The sequence of the amplicons, eliminating the primer regions, was identical in all 13 analyzed plants, and BLAST search indicated that it showed higher similarity to the Italian isolates (Parrano et al. 2012), with the highest (99%) identity to the Italian garlic isolate 218-OYDV6 (GenBank accession no. GQ475367.1) showing only one nucleotide difference. The presence of OYDV in leek plants in the field would represent an alternative host for the infection of onion and garlic crops, and could increase leek crop losses in mixed infections with other viruses. To our knowledge, this is the first report of the detection of OYDV in leek from Spain.