Field observation revealed that the most common symptoms on naturally infected plants in Alexandria, Dakahliya, Kafr Elsheikh and El-Beheira governorates in Egypt were severe mosaic, mild mosaic, chlorosis, mottling, vein banding, blisters, malformation, fern leaf, shoe-string and/or stunting. These symptoms were suspected of being caused by Cucumber mosaic virus (CMV) and confirmed by indirect ELISA. Two samples obtained from wild tobacco and cucumber plants reacted positively with the CMV specific antiserum. Based on symptomology and disease severity on Nicotiana glutinosa and Chenopodium amaranticolor, two isolates of CMV were named CMV-wild tobacco (from Alexandria) and CMVcucumber (from Kafr El-sheikh) and subjected to this study. Reaction of some diagnostic hosts of 11 plant species belonging to five families upon inoculation with the two isolates included different symptoms characteristic to CMVinfection, albeit those induced by CMV-wild tobacco being invariably more severe than those elicited by CMV-cucumber. Identification of virus isolates was confirmed using real time reverse transcription PCR (qRT-PCR). The test isolates demonstrated a single qRT-PCR amplification product of 500bp. The two isolates could be transmitted mechanically and easily transmitted by four aphid species in non-persistent manner. The most efficient vector was Myzus persicae followed by Aphis gossypii, Rhopalosiphum maidis and A. nerii with transmission rates of 90%, 70%, 60% and 50%, respectively, for CMV-wild tobacco and being 80%, 80%, 40% and 30%, respectively for CMV-cucumber. The two isolates could not be transmitted via Cucurbita pepo seeds derived from infected plants. However, virus infection had a great effect on seed germination.

Two isolates of Cucumber mosaic virus (CMV), CMV-wild tobacco (from Alexandria governorate) and CMV-cucumber (from Kafr El-Sheikh governorate) were investigated in this study. Cytological studies on epidermal strips of Nicotiana glutinosa leaves separately infected with each isolate revealed the presence of viral crystalline inclusion bodies within the infected cells. Electron microscopy of ultrathin sections of CMV infected N. glutinosa leaves showed significant alterations in the shape and internal structure of chloroplasts. The cell wall had serrated edges in infected cells but was more severe in cells infected with CMV-wild tobacco isolate compared to those infected with CMV-cucumber isolate. CMV-cucumber isolate was partially purified from systemically infected leaves of N. glutinosa. The ratio A260/ 280 was 1.0 and the concentration of the virus in the preparation was estimated using an extinction coefficient of E260nm0.1%, 1cm = 5. Yield of purified virus was about 2.8 mg/100 g fresh weight of infected N. glutinosa leaves. Electron microscopy of the purified preparation of CMV showed the presence of numerous spherical particles with a mean particle diameter of 28 nm. Amplified real-time reverse transcription-polymerase chain reaction (qRT-PCR) product of coat protein gene of each isolate was purified and sequenced. Sequences of both isolates had been submitted to GenBank Database and ware assigned accession number (LT669766) for CMV-cucumber isolate and (LT706517) for CMV-wild tobacco isolate. The sequences were edited using Chromas Pro. Version 1.34 software and compared with previously subgrouping of 27 isolates of the virus retrieved from the GenBank database. Both CMV-wild tobacco and CMV-cucumber isolates were closely related to the isolate with the accession number AJ585086 with a similarity of 97.07% and 98.54%, respectively, suggesting that the two isolates belong to subgroup II. According to the available literature, this is the first report in Egypt where CMV isolates belonging to subgroup II have been obtained