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A serious disease of groundnut (Arachis hypogaea L.) characterized by stunting of plants, downward roUing, mottling, general chlorosis and reduced size ofthe leaflets was observed in the Sudan, Surveys conducted from 1992 to 1994 showed that this disease was restricted to irrigated groundnut crops grown between the two Niles, The virus had slightly fiexuous filamentous particles (626 nm long) and was transmitted by whiteflies. It was identified seroiogically as cowpea mild mottle virus (CPMMV), This appears to be the first record of natural occurrence of CPMMV on groundnut in the Sudan and the first evidence that it causes a disease of major economic importance. Zusammenfassung Das Cowpea mild mottle virus als Erreger einer schweren Krankheit der Erdnufi im SudanIm Sudan wurde eine schwere Krankheit der ErdnuB {Arachis hypogaea L.) beobachtet. Sie auBerte sich durch folgende Symptome: kummernde Pflanzen sowie nach unten eingeroUte, gescheckte, chlorotische, auffalhg kleine Blattchen. Von 1992 bis 1994durchgefuhrte Untersuchungen zeigten, daB die Krankheit nur auf bewasserten ErdnuBfeldern zwischen dem WeiBen und dem Blauen Nil auftrat. Das Virus war leicht gebogen, fadenformig und 626 nm lang. Es wurde durch WeiBe Fliegen tibertragen und serologisch als Cowpea mild mottle virus (CPMMV) identifiziert. Dies ist offenbar der erste Bericht aber ein natflrliches Vorkommen des CPMMV bei ErdnuB im Sudan und der erste Nachweis, daB dieses Virus eine wirtschaftlich sehr wichtige Krankheit verursacht.

The incidence of Alfalfa mosaic virus (AMV), Potato leafroll virus (PLRV), and Potato virus Y (PVY) in potato crops derived from various types of seed potatoes was assessed visually and confirmed by direct tissue blot immunoassay, over two winter growing seasons (

Two extensive surveys and laboratory work were conducted to determine the occurrence of citrus exocortis viroid (CEVd) and hop stunt viroid (HSVd), the causal agent of cachexia (CVd-IIb) disease in the main citrus growing areas in three states in the northern part of Sudan, viz, Northern, River Nile and Khartoum. For CEVd, all, but one of the examined citrus trees failed to show typical exocortis symptoms. The only symptomatic orange tree encountered in the survey displayed the characteristic CEVd symptoms including tree stunting and bark cracking or bark splitting of the rootstock. While for the cachexia disease, most of the commercial citrus trees were found to be symptomless carriers except mandarin. Symptomatic mandarin trees which were grafted on sour orange rootstock displayed heavy gum impregnation (bark gumming), wood staining and deep bark cracking, in addition to severe stem pitting, bark pegging, twig dieback and yellowing of leaves. Pitting and gum development were usually encountered near the budunion but could spread to other sensitive portions of the infected tree. However, using viroid specific primers and reverse transcription polymerase chain reaction (RT-PCR) approach, both viroids were shown to exist in total RNA preparations from symptomatic and asymptomatic citrus species. Bands of 370 bp and 300 bp corresponding to the full length genomes of CEVd and CVd-IIb, respectively, were detected. The test was positive in 54 for CEVd and 20 for CVd-IIb out of 200 random samples tested from orange, grapefruit and mandarin. The results indicated that a considerably high percentage of citrus species in the northern part of Sudan, particularly in Khartoum State, were symptomless carriers of both CEVd and CVd-IIb. Being rapid, sensitive and in most cases reliable, the molecular approach could be considered indispensable for viroid detection and in testing programs to produce certified viroid-free planting materials.

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