The response of newly introduced plum cultivars to natural infection with Plum pox virus

Plum (Prunus domestica L.) is one of the main fruit crops in Bulgaria. The biggest losses in plum production, as to the other tree species are due to diseases and pests. The aim was to study the response of 12 newly introduced plum cultivars regarding the most important virus disease of plum (Sharka) under conditions of natural infection in Kyustendil region of Bulgaria. The trees of the studied cultivars were planted in a collection plantation at the Institute of Agriculture-Kyustendil in the spring of 2011. Observations of symptom expression were made during vegetation period from 2015 to 2020 by repeated surveys. The disease index (DI) on leaves and fruits was calculated. Leaf samples from the cultivars were tested for the presence of Plum pox virus (PPV), Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV) and Apple chlorotic leafspot virus (ACLSV) by ELISA assay. Under the biotic and abiotic environmental conditions in Kyustendil region on the basis of DI on the fruits, confirmed by ELISA tests the cultivars are divided in 3 groups: tolerant – ‘Black diamond’ and ‘Topstar Plus’; slightly susceptible – ‘Topfirst’, ‘Tophit Plus’, ‘Topking’, ‘Topgigant Plus’, ‘Toptaste’, ‘Top 2000’, ‘Stanley’; Moderately susceptible – ‘Topper’, ‘Top’ and ‘Topend Plus’.