Sharka disease (Plum pox virus) in Turkey: the past, present and future

Sharka disease (caused by Plum pox virus, PPV) was first reported on plum trees in Edirne province of Turkey in 1968. It was later found in Ankara (1972), then in the Marmara region (Bilecik, Bursa, Izmit, Istanbul and Tekirdağ provinces, 1984) and the Aegean region (İzmir, 1986). Further studies in the Aegean and Marmara regions in 1994 showed that PPV was more widespread, and it was detected on plums, apricots and peach trees in more provinces such as Aydin, Balıkesir, Çanakkale, Izmir and Manisa. After that, new survey studies were conducted in different provinces and the virus was also detected in the Mediterranean region (Kahramanmaraş, Adana, Mersin, Hatay, Isparta), Aegean region (Afyon, Kütahya), Central Anatolia (Aksaray, Kayseri, Konya), Marmara region (Kırklareli) and Black Sea region (Samsun). Recently, extensive surveys in Prunus orchards and nurseries were initiated by the Turkish Agriculture, Food and Livestock Ministry within the framework of a National Sharka Project. As a result of this project, important stone-fruit-growing regions were surveyed, new PPV outbreaks were identified and eradication programmes were strictly applied. Serological and molecular characterization studies of Turkish PPV isolates showed that two common strains were PPV-M and PPV-T, of which M appears in recently infected regions, whereas T appears in regions where PPV infection has been known for years. PPV-D has mostly been found as mixed infections with PPV-M, but it has recently also been found as a single infection in Central Anatolia. The most abundant aphid species in PPV-infected regions of Turkey were found to be Myzus persicae, Hyalopterus pruni, Aphis gossypii and Aphis spiraecola, and these species had the highest percentage of viruliferous aphids. Experimental transmission trials confirmed that Myzus persicae was the most efficient vector for PPV-T. When some of the local apricot cultivars such as 'Hacıhaliloğlu', 'Çöloğlu' and 'Şekerpare' were crossed with PPV-resistant apricot cultivars like 'Stark Early Orange', 'Harcot', 'Harleyne' and 'Stella', some progeny were found to be tolerant to PPV. Molecular screening and phenotyping studies are still under way.