New potato virus detected in South America
A virus with bacilliform particles of different sizes (code named SB-22) was isolated from a symptomless cv. Ticahuasi potato plant at the International Potato Center (CIP) in Lima, Peru. The particles of this virus were similar to those of alfalfa mosaic virus (AMV), but preliminary comparative serological studies failed to show any relationship between SB-22 and AMV.
Mechanical inoculations of test plants with crude sap of Physalis floridiana showing mosaic, vein banding and leaf deformation indicated that the virus is sap-transmissible, success depending on the pH of the sap extraction solution, during the summer months of the year.
SB-22 was found to have a wide host range, being symptomless in several hosts. Some hosts react with similar symptoms to both SB-22 and AMV, but AMV symptoms being more severe. The following hosts were found to react with different symptoms than those caused by AMV (Peruvian isolate): Datura metel, D. stramonium, Lycopersicon esculentum, L. pimpinellifolium, Nicandra physalodes, Nicotiana benthamiana, N. rustica, Physalis floridana and Solanum tuberosum (clone DTO 28 and cv. Mariva). The symptoms caused by the virus vary greatly in potato clones making it difficult to detect SB-22 solely by symptomatology. Clone DTO 28 and cv. Mariva react with a yellowing of the foliage and later with necrosis and death of the plant. Glasshouse and field observations indicated that the symptomatology depends on environmental conditions and potato cultivar.
The virus is transmitted by Cuscuta sp., by Myzus persicae, apparently in a semi-persistent manner, and through seeds of P. floridana, S. tuberosum and Capsicum annuum. Infection reduced germination of P. floridana and S. tuberosum seeds up to 84% and 14%, respectively. This reduction is associated with virus-induced necrosis in the seeds. The virus can be detected in non-germinated seeds by DAS-ELISA.
The particle size of SB-22 ranges from 21-368 nm with an average diameter of 25 nm. Five types of particles can be distinguished in purified preparations, the predominant sizes being 21-60 nm. Light and electron microscopy studies of infected P. floridana and S. tuberosum leaves showed that the virus induces the formation of cytoplasmatic inclusion bodies in epidermal and mesophyll cells. These inclusions are amorphous, of variable size, and very stable and numerous in the host tissue.
The virus was found in field samples from different localities in Peru reaching up to 88.4% infection. In the Peruvian highlands the incidence of SB-22 was greater than at the coast. The virus was also found at the Chilean Potato Germplasm collection were 15% of 47 tested clones where infected with the virus and the Robinson Crusoe Island where it infected S. fernandezianum but not cultivated potatoes.
According to the authors, the results of the conducted research provided sufficient evidence to classify SB-22 as a distinct virus from AMV. It is suggested that the virus be considered as a new member of the alfalfa mosaic virus group and the name potato yellowing virus has been proposed.
The International Potato Center in Peru recognises potato yellowing virus as an important virus which should be dealt with as a quarantine problem.
Sources
Fuentes, S.; Jayasinghe, U. (1993) Identification, properties and distribution of a bacilloform virus isolated from potato.
Quartech No. 1, 1993-07, 1-2.
ANON. (1993) Notes on new viruses
Quartech No. 1, 1993-07, 7.