Identification of Onion yellow dwarf potyvirus as One of the Major Viruses Infecting Garlic in Egypt

Onion yellow dwarf potyvirus (OYDV) causes mosaic in garlic plants, together with other Potyviruses, Carlaviruses and Alexiviruses. A garlic isolate of OYDV (OYDV-G) presenting typical yellow stripes was isolated from naturally garlic mixed infected plants and then biologically purified by single local lesion method on leaves of Chenopodium amaranticolor plants. The obtained isolate was mechanically transmitted and caused chlorotic local lesions in C. a maranticolor but necrotic local lesions to C. quinoa and C. Album. The virus had narrow host range, restricted mainly in some plants belonging to family Alliaceae and Chenopodiaceae. The OYDV-G was aphid transmitted in a non-persistent manner through Myzus persicae. Cytoplasmic Cylindrical Inclusions (CI) of pinwheels and laminated aggregates were observed in ultrathin sections of infected garlic leaf cells. The virus was purified from OYDV-infected garlic tissues by modified procedure involved clarification with chloroform and carbon tetrachloride then concentrated by two cycles of centrifugation, first on a 20% sucrose cushion and second on a 0-40% cesium chloride. Ultraviolet absorption spectrum of the purified virus showed a typical curve of nucleoprotein with A sub(260/280) of 1.450-1.560. The yield of purified virus was 12-15 mg kg super(-1) infected garlic leaves. The model length of the purified virus was 725-750 nm. The molecular weight of viral coat protein was 30 kDa when determined by SDS-PAGE. The polyclonal antibodies against OYDV-G were produced and the antiserum titer was determined using repeat-indirect enzyme linked immunosorbant assay (R-ELISA). OYDV-RNA was detected in the purified virus preparation and infected garlic samples by immunocapture/reverse transcription-polymerase chain reaction (IC/RT-PCR) using two oligonucleotide specific primers to amplify the common central region of OYDV coat protein gene with size length of approximately 601 bp. The concentration of the virus in the apical and youngest leaves was relatively low comparing with that in the more mature leaves of garlic plants. In addition, the virus isolate was successfully detected in cloves of garlic.