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2012 Plant Management Network.
Accepted for publication 29 July 2012. Published 24 August 2012.


First Report of Turnip mosaic virus Occurrence in Garlic Mustard in Minnesota


Benham E. Lockhart, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108


Corresponding author: Ben Lockhart.  lockh002@umn.edu


Lockhart, B. 2012. First report of Turnip mosaic virus occurrence in garlic mustard in Minnesota. Online. Plant Health Progress doi:10.1094/PHP-2012-0824-01-BR.


In the summer of 2011 and spring of 2012, plants of the invasive weed species Alliaria petiolata (garlic mustard) were observed in two locations in St. Paul, MN, with virus-like symptoms consisting of conspicuous mosaic (Fig. 1A) and severe stunting. Filamentous potyvirus-like particles 720-800 nm in length were observed by transmission electron microscopy (TEM) in negatively stained, partially purified leaf tissue extracts from symptomatic but not from healthy A. petiolata seedlings. No other virus-like particles were observed. These particles were trapped and decorated by antibodies to Turnip mosaic virus (TuMV), but not by antibodies to Clover yellow vein virus, Potato virus Y, Tobacco etch virus, and Watermelon mosaic virus, four potyviruses that are known to occur in weed and ornamental plant hosts in Minnesota. The identity of the virus associated with the disease symptoms in garlic mustard was further confirmed by reverse-transcription PCR (RT-PCR) using a pair of primers designed from an available TuMV coat protein (CP) genomic sequence (NC_002509) to generate a 463-bp amplicon. These primers, designated TuMV CP-F (5’-TATACACGCCGGAGCAGACG) and TuMV CP-R (5’-CGCAGTGCTGCTGCTTTCAT), were used with total RNA extracted from healthy and infected garlic mustard leaf tissue using an RNeasy kit (Qiagen, Venlo, Netherlands) and Ready-to-Go RT PCR beads (GE Healthcare, Little Chalfont, UK) to amplify a product of the expected size using a thermal cycling program consisting of 42°C for 45 min (1 cycle), 95°C for 5 min (1 cycle), and 35 cycles of 94°C for 20 sec, 58°C for 20 sec and 72°C for 30 sec, with a final extension step of 72°C for 7 min. The 463-bp CP product (Fig. 2) was sequenced and found to have 98% nucleotide sequence identity to homologous CP sequences of known TuMV isolates. To demonstrate proof of pathogenicity, the TuMV isolate from garlic mustard was transferred to healthy Nicotiana benthamiana seedlings by mechanical inoculation and propagated in this host. Inoculum prepared from systemically infected leaves of N. benthamiana was then used to inoculate 12 healthy garlic mustard seedlings which all developed systemic mosaic symptoms 2 to 3 weeks post-inoculation, and became progressively stunted and chlorotic (Fig. 1B). The presence of TuMV in these symptomatic plants, verified by ISEM and RT-PCR as described above, fulfils Koch’s postulates establishing the role of TuMV in the etiology of this disease. Infection of garlic mustard (A. petiolata) by TuMV has been reported previously from Central Europe (1) and Ontario, Canada (2), and TuMV has also been reported to occur in A. officinalis Andrz. in Italy (3). Interestingly, the TuMV isolates (TuMV-Al) from A. officinalis in Italy (3) and A. petiolata in Ontario (2) either did not infect Brassica spp., or were latent in these hosts. In contrast, the Minnesota TuMV Alliaria isolate readily infected and produced distinct mosaic symptoms in both turnip (B. rapa ssp. rapa) and canola (B. napus). The Minnesota Alliaria TuMV isolate also induced in garlic mustard symptoms more severe than those described for the Ontario TuMV-Al isolate (2). Infected first-year garlic mustard plants were severely stunted, and a portion of potted plants kept outdoors did not survive overwintering. Additional studies are needed to determine the effect of the Minnesota Alliaria TuMV isolate on fitness parameters of garlic mustard such as winter hardiness, and seed production and germination rate. The only other report of natural viral infection in garlic mustard in the US is the occurrence of Cucumber mosaic virus in this host in Ohio (4).



A
 
B

Fig. 1. Symptoms observed in Turnip mosaic virus-infected garlic mustard (Alliaria petiolata): (A) mosaic symptoms in naturally-infected plant; (B) stunting and mosaic symptoms in inoculated plant at left, healthy plant at right.


   

Fig. 2. RT-PCR detection of Turnip mosaic virus in garlic mustard (Alliaria petiolata) using the primer pair TuMV CP-F and TuMV CP-R: Lane 1, 100 bp DNA ladder; Lane 2, RT-PCR product (463 bp) from infected plant; Lane 3, healthy control.

 

Literature Cited

1. Horvath, J., Juretic, N., Besada, W. H., and Mamula, D. 1975. Natural occurrence of turnip mosaic virus in Hungary. Acta Phytopath. Acad. Sci. Hung. 10:77-88.

2. Stobbs, L. W., and Van Schagen, J. G. 1987. Occurrence and characterization of a Turnip mosaic virus isolate infecting Alliaria petiolata in Ontario, Canada. Plant Dis. 71:965-968.

3. Lisa, V., and Lovisolo, O. 1976. Biological and serological characterization of the Alliara strain of Turnip mosaic virus. Phytopath. Z. 86:90-96.

4. Boehm, M. J., and Nameth, S. T. 2000. First report of Cucumber mosaic virus in garlic mustard in Ohio. Plant Dis. 84:1047.