الفهرس 
Characterization of Some Viruses Infecting Lettuce in EgyptOnly 14 pages are availabe for public view
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Abstract
1- Field observation revealed that the most common symptoms observed on naturally infected plants in two governorates (El-Fayoum and El-Qalyubia) in Egypt were severe clearing around leaf veins, stunting, thickening of the main veins, crinkling leaves, reduction of head size and deformed lettuce heads. These symptoms were suspected of being caused by lettuce big-vein pathogen (Mirafiori lettuce big -vein virus (MLBVV) and Lettuce big-vein asssocited virus (LBVaV). Applying the DAS- ELISA technique with the use of two polyclonal antisera specific to two viruses, namely, Cucumber mosaic virus (CMV) and lettuce mosaic virus (LMV) has proven that these symptoms were not belonging to CMV or LMV.
2- Identification of two virus isolates was confirmed using the RT-PCR technique with a pair of specific primers for coat protein gene of each virus and the generation of a unique PCR amplification product of approximately ≈233 bp (MLBVV) and approximately ≈360 bp (LBVaV), respectively.
3- The amplicons obtained were purified and sequenced using ABI PRISM model 310 automated DNA sequencer. Sequences related to the three virus isolates were submitted to Genbank database under the accession numbers, LT721898, LT721899 and LT721900.
4- The highest similarity percentage was observed between MLBVV1 and MLBVV2 and Spain isolate was 70.3% and 69.7%, respectively. While, the highest similarity percentage between LBVaV1 and Brazil isolate with similarity percentage of 100%.
5- The ultraviolet absorbance of the purified virus preparation was typical for nucleoproteins with a minimum at 240 nm and a maximum at 260nm. The ratio of A260 / A280 was 1.94. The yield of purified virus was 1.2mg/100g infected lettuce leaves.
6- Detection of MLBVV, LBVaV, and Olpidium virulentus in the seeds collected from infected plants was possible using molecular analysis (RT-PCR and PCR).
7- Electron microscopy of a purified preparation of MLBVV and LBVaV complex showed MLBVV as highly kinked filaments about 3 nm in width forming masses of undetermined length, while LBVaV was observed as a few straight rigid rod-shaped particles of a modal length of about 300 nm and a width of 18 nm. While examination of infected leaf crude sap showed the presence of only LBVaV virions as MLBVV particles were not detectable.