Submitted to: Proceedings Mint Industry Research Council
Publication Type: Proceedings
Publication Acceptance Date: November 30, 2004
Publication Date: January 26, 2005
Citation: Postman, J.D., Martin, R.R., Tzanetakis, I. 2005. Characterize new viruses in mint germplasm. Proceedings Mint Industry Research Council. 5:72-77. Interpretive Summary: We recently detected five viruses previously unknown in mint in North America from plants that are commercially available at nurseries throughout the United States. Strawberry latent ringspot virus was detected in the ornamental ‘Golden Ginger Mint’, but is not significant to the mint industry. Two of the new viruses are in the closterovirus family. Viruses in this family can spread rapidly if an appropriate insect is present. We have shown that both of these viruses are likely to be spread by aphids. The disease-causing potential of these two mint viruses is not know. Many of the plants found to be infected exhibited no visible symptoms. The fourth virus is in the Potexvirus family, which includes viruses that are mechanically transmitted. This virus could potentially be spread by mint harvesting equipment. The fifth new virus is similar to one found in grapes. Some viruses only produce symptoms when they infect a plant in combination with other viruses. Accumulated infections with multiple viruses may be the cause of a decline in some mint fields where the fungal disease verticillium wilt is not present. The yellow symptoms observed in ‘Golden Ginger Mint’ may also be the result of the combined infection with multiple viruses. We have developed molecular detection tools for these five mint viruses.
Technical Abstract: Three viruses not previously reported from mint in North America were detected in a variegated Mentha × gentilis clone at the USDA mint germplasm collection in Corvallis, Oregon. Molecular data was obtained after cloning from double stranded RNA (dsRNA) and primers were designed for RT-PCR detection of all three viruses. Genomic sequences from two of the viruses, a potexvirus and a closterovirus did not correspond to those of any known virus. The third virus was identified as Strawberry latent ringspot virus (SLRSV), a European virus not known to occur in North America. Antiserum was developed against the mint isolate of SLRSV and was compared against other SLRSV antisera for detection by ELISA. Variegated M. x gentilis (= ‘Golden Ginger Mint’) plants were obtained from nurseries in Maryland, Michigan, Nebraska, Ohio, and Oregon. All of the ‘Golden Ginger Mint’ plants from commercial nurseries tested positive for the potexvirus found in the USDA clone. The closterovirus and the mint isolate of SLRSV were found in some but not all of the nursery plants. Plants of other assorted mint species were obtained from additional wholesale and retail nurseries, and peppermint and spearmint samples were collected from commercial fields in western Oregon. These plants were found to be free of SLRSV, but some plants from all sources were found to be infected with the new closterovirus. Three NCGR mint clones with mild veinbanding symptoms were found to be infected with Tobacco ringspot virus. A ‘Ginger Mint’ from an Oregon nursery did not exhibit yellow vein-banding typical of the other samples, and did not contain any of the viruses found in the other ‘Golden Ginger Mints.’ Cloned dsRNA from this plant revealed the presence of a second closterovirus and a flexivirus, belonging to the genus Vitivirus. Sequence data from these viruses does not correspond to other know plant viruses. PCR tests indicate that the second closterovirus is also present in symptomless plants from other nursery sources. Aphid, sap and graft transmission tests were initiated to determine how these viruses might spread, and also to attempt to separate the viruses from plants with multiple infections. Preliminary results suggest that both closteroviruses and the vitivirus may be aphid transmitted. We strongly suspect that the new potexvirus is responsible for veinbanding in M. x gentilis, but the combination with a second virus may be required for expression of the strong symptoms observed in the ornamental ‘variegated’ clones or ‘Golden Ginger Mint’ found in the nursery trade.