Papaya ringspot virus‐P: characteristics, pathogenicity, sequence variability and control

Taxonomy: Papaya ringspot virus (PRSV) is an aphid‐transmitted plant virus belonging to the genus Potyvirus, family Potyviridae, with a positive sense RNA genome. PRSV isolates belong to either one of two major strains, P or W. The P strains infect both papaya and cucurbits whereas the W strains infect only cucurbits. Geographical distribution: PRSV‐P is found in all major papaya‐growing areas. Physical properties: Virions are filamentous, non‐enveloped and flexuous measuring 760–800 × 12 nm. Virus particles contain 94.5% protein and 5.5% nucleic acid. The protein component consists of the virus coat protein (CP), which has a molecular weight of about 36 kDa as estimated by Western blot analysis. Density of the sedimenting component in purified PRSV preparations is 1.32 g/cm³ in CsCl. Genome: The PRSV genome consists of a unipartite linear single‐stranded positive sense RNA of 10 326 nucleotides with a 5′ terminus, genome‐linked protein, VPg. Transmission: The virus is naturally transmitted via aphids in a non‐persistent manner. Both the CP and helper component (HC‐Pro) are required for vector transmission. This virus can also be transmitted mechanically, and is typically not seed‐transmitted. Hosts: PRSV has a limited number of hosts belonging to the families Caricaceae, Chenopodiaceae and Cucurbitaceae. Propagation hosts are: Carica papaya, Cucurbita pepo and Cucumis metuliferus cv. accession 2459. Local lesion assay hosts are: Chenopodium quinoa and Chenopodium amaranticolor. Control: Two transgenic papaya varieties, Rainbow and SunUp, with engineered resistance to PRSV have been commercially grown in Hawaii since 1998. Besides transgenic resistance, tolerant varieties, cross‐protection and other cultural practices such as isolation and rogueing of infected plants are used to manage the disease. Virus code: 00.057.0.01.045. Virus accession number: 57010045. Useful link: http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/57010045.htm