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United States Department of Agriculture

Agricultural Research Service

Title: Detection and Characterization of Two Previously Undescribed Potyviruses in the Terrestrial Orchid Spiranthes Cernua

Authors
item Guaragna, Mary Ann
item Odum, Obinna - STUDENT, UNIV. OF MD
item Jordan, Ramon

Submitted to: Acta Horticulture Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 16, 2005
Publication Date: October 31, 2006
Citation: Guaragna, M.A., Ndum, O., Jordan, R.L. 2006. Detection and characterization of two previously undescribed potyviruses in the terrestrial orchid Spiranthes cernua. Acta Horticuture. 722:209-218.

Interpretive Summary: Orchids form a large part of the floral trade in ornamental plants and cut flowers and are the largest family of flowering plants with more than 35,000 species. Orchids grow naturally in a wide range of habitats in many parts of the world. Grown commercially in many countries, orchids have perhaps the highest unit value of any commercial pot plant. Viruses infecting orchids are a serious threat to the industry as they reduce vigor of infected plants and decrease foliage and flower quality. Over a dozen viruses, mostly potyviruses, have been recorded in orchid. Spiranthes cernua is a terrestrial orchid that grows in moist areas in the southeastern US. Cultivated varieties are now also being used as flowering perennials. We have previously reported Dasheen mosaic virus (DsMV-Sc) infection in commercially-grown plants exhibiting chlorotic blotching and/or mosaic symptoms. Other similarly symptomatic plants were, however, ELISA negative using DsMV polyclonal antisera, yet gave a positive reaction with the broad-spectrum potyvirus monoclonal antibody PTY 1, an antibody specific for a highly conserved site in the potyviral coat protein. The 3' terminal portion of this unknown potyvirus was cloned and sequenced and compared to the corresponding regions of other potyviruses. This analysis revealed the presence of two unique sets of potyviral sequences, neither of which had any significant identity with each other (56% CP identity and 39% 3'NCR identity), nor with DsMV (49-53% CP, 33-43% 3'NCR), nor with any other potyvirus sequence (<64% CP identity and <57% 3'NCR identity) currently in the GenBank database, including other orchid-infecting potyviruses. Pairwise alignments and analysis of the coat protein amino acid sequences and 3' NCR regions confirm the classification of these two viruses as new potyvirus members. We have tentatively named these two new potyviruses Spiranthes mosaic virus (SpiMV) 2 and SpiMV 3. This is only the second report of any virus infection in the genus Spiranthes and the first report of two new potyviruses infecting a member of the Orchidaceae. This information should help verbena growers and producers develop virus-free materials.

Technical Abstract: Spiranthes cernua is a terrestrial orchid that grows in moist areas in the southeastern US. Cultivated varieties are now also being used as flowering perennials. We have previously reported Dasheen mosaic virus (DsMV-Sc) infection in commercially-grown plants exhibiting chlorotic blotching and/or mosaic symptoms. Other similarly symptomatic plants were, however, ELISA negative using DsMV polyclonal antisera, yet gave a positive reaction with the broad-spectrum potyvirus monoclonal antibody PTY 1, an antibody specific for a highly conserved site in the potyviral coat protein. Total RNA extracts from infected leaves were used in RT-PCR assays with generic potyvirus-specific primers which amplify various highly conserved 335, c.700, or c.1600bp fragments from the 3' terminus of most potyviruses which includes the 3' non-coding region (3'NCR) and the potyviral coat protein (CP). The PCR amplified fragments were subsequently cloned and sequenced and compared to the corresponding regions of other potyviruses. This analysis revealed the presence of two unique sets of potyviral sequences, neither of which had any significant identity with each other (56% CP identity and 39% 3'NCR identity), nor with DsMV (49-53% CP, 33-43% 3'NCR), nor with any other potyvirus sequence (<64% CP identity and <57% 3'NCR identity) currently in the GenBank database, including other orchid-infecting potyviruses. Pairwise alignments and Clustal W analysis of the coat protein amino acid sequences and 3' NCR regions confirm the classification of these two viruses as new potyvirus members. We have tentatively named these two new potyviruses Spiranthes mosaic virus (SpiMV) 2 and SpiMV 3. This is only the second report of any virus infection in the genus Spiranthes and the first report of two new potyviruses infecting a member of the Orchidaceae.

Last Modified: 12/21/2014
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