Purification and Characterization of a Jordanian Isolate of Watermelon Mosaic Virus

The Jordanian isolate of watermelon mosaic virus-2 (WMV-2Jo) was purified from infected Cucurbita pepo cv. Top Capi by extraction in 0.05 M sodium citrate buffer containing 0.01 M sodium diethyl dithiocarbamate and 0.01 M cysteine hydrochloride (0.01 M D + C), clarification with chloroform and n-butanol, sedimentation by ultracentrifugation, and rate-zonal centrifugation in 10–40% sucrose gradient. The purified virus had an ultraviolet absorption spectrum typical of a nucleoprotein with a low nucleic acid content. Homologous antiserum had a titre of 1: 256, as determined by the ring interface test. Electron microscopy of negatively stained purified virus revealed flexuous particles with a normal length of 750 nm. Cytoplasmic spindle-shaped inclusions were readily detectable in infected epidermal cells under the light microscope. Thin sections of infected tissue revealed the presence of laminated aggregates, pinwheel and scroll inclusions. The virus reacted with antisera prepared to the Florida strain of WMV-2 and zucchini yellow mosaic virus in a sodium dodecyl sulfate (SDS) agar gel diffusion test. Using the Derrick-decoration combined technique of immune electron microscopy, the virus reacted strongly with the homologous antiserum and zucchini yellow mosaic virus antiserum, but less with antiserum prepared to the Florida strain of WMV-2.