|Gudmestad, N - N. DAKOTA ST. UNIV|
|Mallik, I - N. DAKOTA ST. UNIV|
|Pasche, J - N. DAKOTA ST. UNIV|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2008
Publication Date: August 1, 2008
Citation: Gudmestad, N.C., I. Mallik, J.S. Pasche, and J.M. Crosslin. 2008. First report of tobacco rattle virus causing corky ringspot in potatoes grown in Minnesota and Wisconsin. Plant Disease 92:1254. Interpretive Summary: When tobacco rattle virus (TRV) is transmitted by stubby root nematodes to developing potato tubers, it causes a disease called corky ringspot (CRS) due to the symptoms that are produced. The disease can cause significant economic losses and entire fields may be rejected if the disease incidence is high. CRS has previously been reported from Oregon, Washington, Idaho, Colorado, Florida, and was recently reported in Michigan. This is the first report of CRS caused by TRV in the states of Minnesota and Wisconsin.
Technical Abstract: In July 2007, potato tubers cv. Russet Burbank (RB) with necrotic arcs and spots were detected in three fields in Buffalo County, Wisconsin and one field in Benson County, Minnesota. Umatilla Russet (UR) potatoes harvested from the west half of a field in Swift County, MN had similar, but visually distinct necrotic lesions. Portions of one field in MN were abandoned and the stored potato crop from two fields in WI was rejected by processors, representing a total crop loss due to tuber necrosis. The tuber symptoms displayed by tubers in both cultivars resembled those described for corky ringspot caused by Tobacco rattle virus (TRV). Total RNA was isolated from necrotic tuber tissue crushed in liquid nitrogen and extracted using the Total RNA isolation kit (Promega Corp.). These extracts were tested for the presence of TRV by reverse transcription (RT)-PCR using primers complementary to nucleotides 6555-6575 and identical to nucleotides 6113-6132 within the 3’ terminal open reading frame of TRV RNA-1. The expected 463 bp fragments were amplified from RB tubers. Nucleotide sequences from a WI and MN isolate (EU569290 and EU569291, respectively) were 99-100% identical to the corresponding region in a published TRV sequence (accession AF055912). A 396 bp fragment was amplified from UR tubers and sequence data (EU569292) indicated a unique 63 nucleotide sequence was substituted for a 129 nucleotide sequence spanning residues 227-357 of the 463 bp amplicon from RB TRV isolate. A total of seven fragments were sequenced from different UR tubers and the 396 bp fragment was identical among them. The sequence outside the substituted region had 92% identity to the published TRV sequence. Amplification of the full length TRV RNA2 using the primers 179/180 located in the 5’ and 3’ untranslated regions was successful for 28% and 0% of the RB and UR samples, respectively, suggesting that the RNA2 is not present in these strains or has undergone significant mutation. TRV-infected sap from both potato cultivars was mechanically transmitted to tobacco cv. Samsun NN and these plants subsequently tested positive for TRV by ELISA using ATCC antiserum PVAS 820. Ninety tubers exhibiting mild to severe symptoms of TRV were planted in the greenhouse. Each tuber was bisected laterally; necrotic tissue was removed from one half of the tuber and tested for the presence of TRV using RT-PCR protocols described above RNA1. The remaining half was bisected horizontally and both sections were planted. Foliage from each emerged plant was subsequently also tested by RT-PCR for TRV RNA1. RB tubers from WI tested positive for TRV, but only 7 of 24 emerged plants tested positive. Only 72% and 4 of 25 emerged plants and tubers from MN UR tested positive. TRV has been confirmed in California, Colorado, Florida, Idaho, Michigan, Oregon and Washington. We believe this is the first report of corky ringspot in potato caused by TRV in MN and WI.