RESUMEN
Mosaic symptoms were observed on pepper plants in Riyadh region [Wasil fields], Saudi Arabia. Out of 16 plant species mechanically inoculated with sap prepared from leaves of infected pepper plants in 0.1 M potassium phosphate buffer, pH 7.0,13 plant species were infected and exhibited external symptoms. These included: Chenopodlum amaranticolor Goste and Ryen., C. quince, Capsicum annuum L Datura stramonium, Gompbrena globosa L, Lactuca romana, Lycopersicon esculentum Mill., cultivar Sultana, Medlcago sativa L, Solanum melongena L. cultivar Black beauty, Solanum nlgrum, Nicotians glutinosa L., N. tadaccum, and Pbaseolus vulgaris L. cultivar Green beans. CucurUta pepo L., and Cucumis sativus L. did not show symptoms. The properties of virus in the infective sap were as follows: Thermal Inactivation point [TIP] was between GOTO0 C, dilution end point [DEP] was between 10[3] -10[4] and the longevity In Vitro [IV] was between 2-4 days. ELISA indicated that the virus was alfalfa mosaic virus [AMV]. Inoculation of some pepper cultivars with this AMV isolate resulted in external virus symptoms which were variable among the different inoculated pepper cultivars. Determination of the total protein in the different pepper cultivars revealed higher protein contents in the inoculated cultivars compared to those which were not inoculated with AMV. Seven plant species [Nlcotiana glutinosa L., Datura stramonium L, Chenopodium amaranticolor tost and Ryen, Gomphrena globosa L, Capsicum annuum L., Solanum nlgrum L., Phaseolus vulgaris L.] out of 11 plant species mechanically inoculated with the virus isolate, and showed AMV-like symptoms on them. ELISA indicated that the naturally infected pepper plant as well as the seven inoculated host plants that showed different symptoms, and were all positive to AMV. Four pepper varieties were infected with the virus and that the effect of the virus varied for the different cultivars with respect to the type and severity of symptoms expressed on them and which included mosaic, yellow mosaic, calico, mottle, leaf curl and deformation, cupping, and necrosis of the interveinal areas of lamina in some pepper cultivars. ELISA also indicated that it is not necessary that the severity of symptoms and virus concentration in the infected plants are always directly proportional