First Report of Barley Yellow Dwarf Virus-PAV Infecting Oats (Avena sativa) in Taiwan

Abstract

Barley yellow dwarf virus is a group of positive-sense single stranded RNA viruses with many species belonging to the family Luteoviridae and known to cause significant yield losses of cereal crops worldwide (Irwin and Thresh 1990). Oat (Avena sativa L.), a temperate cereal crop usually grown as forage in subtropical regions, has been recently reintroduced into Taiwan as a local winter forage source. In April 2017, yellowing, V-shape reddening, and purple symptoms were observed on 7.9% of the mature leaves of the oat plants grown in the experimental field of National Taiwan University (NTU) in Taipei city, Taiwan. We collected 37 leaf samples with suspected virus-infection symptoms in the experimental field for virus screening. The samples were expressing varying degrees of yellowing, browning, or typical barley yellow dwarf virus (BYDV)-associated V-shape reddening and purple symptoms. An additional five samples with no symptoms were also collected. These 37 samples belong to 22 oat lines, including two registered cultivars and 20 unreleased breeding lines. Some lines were replicated in the field and therefore were sampled more than once. A specific reverse transcription polymerase chain reaction assay (RT-PCR) for BYDV, covering the coat protein (CP) gene and partial RNA-dependent RNA polymerase regions, was performed with the primers Shu-F (5′-TACGGTAAGTGCCCAACTCC-3′) and Yan-R (5′-TGTTGAGGAGTCTACCTATTTG-3′) on the extracted total RNA of the samples (Malmstrom and Shu 2004). Among the examined samples, only the three expressing typical BYDV symptoms tested positive, whereas the other 34 samples with solely yellowing or browning symptoms and the five symptomless samples tested negative. The samples belonged to the cultivar Swan and two breeding lines, 15-39 and 16-47; the seeds of the three symptomatic oats were all imported from the United States. We further cross-examined the three positive samples with another RT-PCR assay, using specific primer pairs targeting the BYDV CP gene (for strains PAV, MAV, and GAV): Luteo1F (5′-TTCGGMSARTGGTTGTGGTCCA-3′) and YanR-new (5′-TGTTGAGGAGTCTACCTATTTNG-3′) (Mustafayev et al. 2013; Svanella-Dumas et al. 2013). The electrophoresis analysis of the RT-PCR amplicons revealed the expected 545-bp fragment from all. The amplicons were later cloned into pCR2.1-TOPO (Invitrogen, Carlsbad, CA) for sequencing analysis. All of the sequences obtained were identical (GenBank accession nos. MF618251, MK361042, and MK361043) and showed 99% similarity to the BYDV-PAV isolates from the United States (accession nos. EF521840 and DQ115532) in GenBank. Based on the phylogenetic analysis of CP gene sequences, the BYDV-PAV Taiwan isolates and these two U.S. isolates were in the same cluster. To further confirm the results, the BYDV-PAV specific enzyme-linked immunosorbent assay on the three symptomatic samples, using the commercialized kit (Agdia, Elkhart, IN), also aligned with the prior assay and showed positive reaction results. To our knowledge, this is the first report of BYDV-PAV in Taiwan. The phylogeny analysis of the virus suggests the BYDV-PAV might have been introduced through the seeds, which had gone through one cycle of multiplication at the border between Idaho and Oregon states prior to growing in Taiwan. Because the BYDV infection on oat presented a threat to cereal crop production in Taiwan, all oat plants in the NTU experimental field were eliminated immediately to prevent the spread of the disease. Agricultural agencies were informed of the incidence, and oat growers were educated to identify the BYDV symptoms on oat. Further field surveys of BYDV on the alleged vector insects will be carried to better understand the disease biology in Taiwan and to provide information on the disease system in the Southeast Asia region.