Double infections with cucumber mosaic virus and plum pox virus (Sharka) in apricot trees

Abstract

Cucumber Mosaic Virus (CMV) and Plum Pox Virus(PPV) (Sharka) were isolated from naturally infected apricot (Prunus armeniaca cv. El-Amar) trees showing leaf mottling, marginal leaf necrosis deformation and abortive flowers grown at Kalubia and el-Fayoum Governorates, Egypt. The identities of the two viruses were confirmed serologically using DAS-ELISA. Graft inoculation of diseased apricot scion onto healthy one showed the same symptoms as those seen in naturally infected trees in the stock shoots. Similar symptoms were caused by slashing inoculation with surgical knife onto the stem of young healthy apricot seedling with mixed inoculum of both viruses of CMV and PPV. CMV was biologically purified from single local lesions which formed on cucumber cotyledon and/or Chenopodium quinoa. Identification of this virus was based on host range, trans mis sibility and serological tests. CMV was able to infect only 20 plant species and varieties out of 24 tested plants by either grafting or mechanical inoculation and PPV was able to infect only 19 plant species and varieties. CMV and PPV can be transmitted by Aphis gossypii and Myzus persicae from cucumber to cucumber and woody plants. The best time for leaf sampling was to detect the viruses, in diseased apricot tree by sap inoculation or ELISA, in April, followed by May and June. Double infection by PPV and CMV of apricot trees resulted in synergistic effect where symptoms in doubly infected plants were more severe than that in plants singly infected by either viruses. ELISA values revealed that the concentration of CMV in doubly infected apricot plants is significantly higher than that of single infected plant. Increase of CMV in doubly infected apricot was confirmed by local lesion assays and specific infectivity. However, PPV titer did not increase significantly in case of double infection compared to singly infected plant. Reverse transcription-polymerase chain reaction (RT-PCR) amplified 500 bp fragment and 335 bp from infected plant using degenerate oligonucleotide primer specific for potyviruses group and oligonucleotide primer specific for CMV. The results showed also that such multiplex RT-PCR can detect the two viruses either each alone or both together in samples collected from artificially or naturally infected plants. © 2012 Academic Journals Inc.