The Viruses and Virus Diseases of Cassava in Africa

Abstract

This review summarises the available information on the viruses and virus diseases of cassava in Africa. It then considers the distribution, prevalence and epidemiology of the two most important of these diseases: African cassava mosaic, which occurs in all the main cassava-growing areas, and cassava brown streak, which seems to be restricted to parts of eastern and southern Africa. The epidemiology of African cassava mosaic has been studied in few of the very diverse agro-ecological zones in which the disease occurs and there is even less information on brown streak. These are serious constraints in attempts to develop effective control measures. Information is also lacking on possible interactions between the two diseases and on their effects on the response of cassava to bacterial blight and other diseases and also to arthropod pests, nematodes and weeds. This emphasises the scope for a multi-disciplinary holistic ecological approach in any further studies aimed at developing fully integrated control measures to combat the whole range of cassava pests, diseases and weeds. Key Words : African cassava mosaic, cassava brown streak, whitefly vector, Bemisia tabaci Ce texte r e sume l'information disponible sur les virus et maladies virales du manioc en Afrique. Il traite ainsi de la r e partition, de l'incidence et de l' e d e miologie des deux principales maladies virales du manioc: la mosa i que africaine du manioc pr e sente dans toutes les principales zones de culture du manioc, et le cassava brown streak qui semble  e tre limite  a  certaines parties de l' Afrique de l 'Est et d 'Afrique australe. L 'epidemiologie de la mosa i que africaine du manioc ete etudiee dans quelques unes seulement des diverses zones agro-ecologique o u  se trouve la maladie et il y a encore moins d'information sur brown streak. Les tentatives de contr o le de la maladie se heurtent ainsi a  de serieuses difficultes. Il n'y a pas suffisamment d'information non plus sur les interactions possibles entre les deux maladies et sur la reaction du manioc vis a vis d 'autres maladies, arthropodes, nematodes et mauvaises herbes ennemis du manioc. Ceci souligne la necessite d'une etude ecologique multidisciplinaire de la biocenose parasitaire du manioc afin de developper une lutte integree contre l'ensenble des ennemis de la culture. Mots Cl e s : Mosa i que africaine du manioc, cassava brown streak, aleurode, Bemisia tabaci