In spring 2015, 12 weedy garlic mustard (Alliaria petiolata) plants with mosaic symptoms were found in a garden in State College, PA. The same symptoms are seen on many weedy garlic mustards in the area each spring, as they were in previous years at this location. Incidence was ∼10% in the garden, with 2 of ∼20 groups of 4 to 6 plants infected. Quality of RNA extracted from garlic mustard was poor, so symptomatic leaves were used for mechanical transmission to Nicotiana benthamiana. Seven days after mechanical inoculation, plants showed necrotic spots and leaf deformation on the systemic leaves. Double-stranded RNA was extracted from symptomatic N. benthamiana leaves and electrophoresis was performed on 6% polyacrylamide gel to detect dsRNA, produced in plants infected with RNA viruses (Valverde et al. 1990). A band of high molecular weight confirmed the presence of dsRNA. Total RNA was then extracted from the N. benthamiana plants using Spectrum Plant Total RNA Kit (Sigma-Aldrich). A tobravirus or a potyvirus were suspected as possible causal agents, based on literature search for the potyvirus and on the presence a tobravirus infected ornamental plant in the same garden. Two pairs of degenerate primers (Chen et al. 2001; Jones et al. 2008) were used separately in one tube reverse-transcription PCR (RT-PCR) and 835-bp and 654-bp amplicons were cloned into pGEM-T Easy Vector (Promega) and sequenced by Sanger sequencing. The sequences were deposited as GenBank Accession Nos. KT799530 and KT799528, respectively. BLAST results showed that the first sequence had 96% nucleotide identity with the RNA dependent RNA polymerase (RdRp) of a previously reported White clover mosaic virus (WClMV) sequence (AB669182). The second sequence had 95% nucleotide identity to a Turnip mosaic virus (TuMV) sequence across the NIb and coat protein genes (AB252117). Two newly designed primer pairs W_1F (5′-CAGAACGAGCCATCCGCAGAA), W_1500R (5′-TCAGTGCAGTCAGCATTATGAG) and TuMV_F (5′-TCTTGGACGAAGCATGGAGC), TuMV_R (5′-TCGGACTGCCTCTTTGCCTG) were used to further confirm the presence in N. benthamiana of WClMV and TuMV, respectively. A 1,457-bp amplicon was obtained by using W_1F and W_1500R and sequenced. This sequence (KT799531) had 95 to 96% nucleotide identity with several WClMV RdRp sequences (AB056720, AB669182, and X16636). A 577-bp amplicon was obtained by using the primer pair specific to TuMV sequence. The sequenced amplicon (KT788529) showed 97% nucleotide identity to a TuMV sequence spanning the P3 and 6K1 protein (AB701705). Due to the poor quality of RNA we could not test the original or other garlic mustard plants for the presence of the two viruses, but all weeds had uniform symptoms appearance and severity. To our knowledge, White clover mosaic virus and Turnip mosaic virus have not been previously reported in garlic mustard plants in Pennsylvania. Other potyviruses including TuMV have been reported in garlic mustard and Brassicaceae while WClMV to our knowledge was never reported in Brassicaceae or in garlic mustard before. TuMV is a member of the Potyviridae family, is transmitted by aphids in a nonpersistent manner, and causes a variety of symptoms in many Brassica spp.(Tomlinson and Ward 1978) The presence on garlic mustard of a strain of TuMV very similar to a strain already reported in Europe on arugula (Eruca or Brassica vesicaria subsp. sativa) could indicate that this virus can be transmitted between cultivated and not cultivated Brassicaceae and that wild Brassicaceae can potentially serve as virus reservoir (Lockhart 2012). The mode of transmission of WClMV is not known and reports of its transmission by contact or by dodder (Cuscuta spp.) (probably under experimental conditions) have been controversial; therefore, it is hard to speculate if this virus can move from crops to natural environment and vice versa. This is the first report of infection of garlic mustard with TuMV and WClMV, which have the potential to reduce the fitness of this plant species that is considered invasive in North America.
All Science Journal Classification (ASJC) codes
- Agronomy and Crop Science
- Plant Science