James: Plum pox virus variability
Plum pox (Sharka); the disease and variability of the virus
Sidney Laboratory - Centre for Plant Health, Canadian Food Inspection Agency, North Saanich, BC. Canada, V8L 1H3
Symptoms of plum pox (Sharka) were observed for the first time around 1917-1918 in Bulgaria, and the first description of the disease was by Prof. Dimitri Atanasoff, in the University of Sophia Yearbook, Volume 11 (1932/1933), which was published in 1933. Atanasoff compared the disease to Buckskin disease of cherry and stated that it is a very destructive disease that threatened the very existence of plum cultivation in Bulgaria. Symptoms of the disease include necrotic lesions on fruit, fruit deformity, premature fruit drop, flower colour breaking, rings on fruit/stones/leaves, bark splitting, and tree decline. Biochemical effects on the fruit may include decreased sugar content, decreased anthocyanin content, and increased acid content. In some susceptible cultivars diseased fruit may be unsuitable for direct consumption or for industrial processing (Nemeth, 1986). It has been estimated that in Europe losses due to the disease over the past 20 – 30 years are approximately 13 Billion USD (Cambra et al. 2006). The disease is caused by Plum pox virus (PPV), a positive sense single stranded RNA virus, a member of the genus Potyvirus, family Potyviridae. The virus encodes two open reading frames (ORF): a major ORF encoding a polyprotein that is cleaved post-translation into the functional proteins, and a minor ORF that encodes a protein identified as PIPO (Pretty Interesting Potyviridae ORF) that seems to be involved in virus movement. RNA-dependent RNA polymerase responsible for RNA virus replication lacks proof reading capacity. This along with recombination events has produced genetic variability of the virus genome that has resulted in the identification, to date, of nine strains/subgroups of PPV: D, M, EA, C, Rec, W, T, CR, An (James et al. 2013). Unique genetic diversity associated with each strain allows for the development of strain specific diagnostic tools (both nucleic acid-based and protein/serology-based). Strains, also isolates of the same strain, may differ in their geographic distribution; and in their biological properties such as host range, symptom severity, and transmissibility. The virus is transmitted in a non-persistent manner by aphids and this potential for insect transmission contributes to challenges associated with successful eradication or management of the virus.
Atanasoff, D. 1933. Plum pox. A new virus disease. Faculty of Agriculture and Forestry, University of Sofia Yearbook (1932-1933) Vol 11: 49-69.
Cambra, M., Capote, N., Myrta, A., and Llacer, G. 2006. Plum pox virus and the estimated costs associated with sharka disease. EPPO Bulletin 38: 202-204.
James, D., Varga, A., and Sanderson, D. 2013. Genetic diversity of Plum pox virus: strains disease and related challenges for control. Canadian Journal of Plant Pathology 35:431-441.
Nemeth, M. 1986. Plum pox (sharka) In M. Nemeth (Ed.) Virus, Mycoplasma and Rickettsia Diseas3s of Fruit Trees (pp. 463-479). Budapest: Akademiai Kiado