[Occurrence and characterization of cowpea mild mottle virus "CMMV" naturally infecting groundnut in Khartoum State [Sudan]]

During a survey for the incidence of viruses in groundnut (Arachis hypogaea L.) IN 1991, a new virus disease was observed on groundunt grown around Khartoum showing characteristic downward rolling of young quadrifoliate leaf margins and vein-banding and mottling on order leaves. Infected plants were severely stunted. The present study concerns the isolation, identification and characterization of the causal agent of the disease. The virus has been isolated successfully from naturally infected groundnut, using 0.05M phosphate, pH 7.4+ 0.01 sodium sulphite. Sub sequently, the virus was maintained on soybean and cowpea plants using the standard sap inoculation technique. The sap transmission of the virus was performed with some difficulty in absence of inoculum additives, particularly when using groundnut as a donor or test species. However, using of reducing and stabilizing agents helped greatly in enhancing the transmission of the virus. The combination of 0.01 sodium diethldithiocarbamate (NaDIECA) and 0.01 thioglycolic acid gave the highest transmission percentage (60) when virus transmission was made from groundnut to groundnut. Sap transmission from groundnut to other hosts (e.g cowpea) was enhanced greatly (about 90) when the extraction medium contained Na2SO3 + NaDIECA. The lost range of the virus was found to be confined greatly to plant species in the family Leguminosae in addition to two Chenopodium species and Beta vulgaris. Inoculated groundnut plants reacted initially with vein-clearing and downward rolling of the newly emerged quadrofoliate leaves 7 to 10 days post-inoculation follwed by chlorotic rings and systemic chlorosis. Infected plants were severely stunted and showed vein-banding and mottling on older leaves. Cowpea (Vigna unguiculata), bean (Phaseolus vulgaris), and soybean (Glycine max) reacted systematically with the virus, while chenopodium quinoa, C. amanranticolor and Beta vulgaris reacted with local lesions. Soybean, beet root, chenopodium quinoa and phaseolus vulgaris cv. "Red kidney" were considered as good diagnostic hosts for the virus. The virus failed to infect the following hosts: Cucumis sativus, Citrullus sp., Cucurbita maxima, Cajanus cajan, Clitoria sp., Datura stramonium, D. metel Lycopersicon esculentum, Nicotiana tabacum, N. rustica, N. glutinosa, N. debneyi, Capsicum annum, Solanum melongena, Petunia hybrida and Vicia faba. All groundnut cultivars grown in Sudan were found to be readily infected except cv. "El-Abbassia" which seemed to be non-susceptible to the virus. Infection levels ranging from 0.0 to 100 were obtained using mechanical inoculation. The virus was found to be moderately stable in crude sap having DEP of 10-4-10-5, TIP between 65-70C and longevity in vitro of 3-4 days when stored at 22-250C. The virus was found to be transmitted by whiteflies (Bemisia tabaci) in a non-persistent manner.