Bacterial Blight of Cassava in Togo: Its Importance, the Virulence of the Pathogen and the Resistance of Varieties

Abstract

Cassava, Manihot esculenta Crantz, is one of the most important food crops in tropical Africa. It is the source of dietary food energy for the majority of people living in the lowland humid tropics of West and Central Africa (FAO, 1984; IITA, 1989). Cassava is also a major source of cash income for smallholder households and a low-cost carbohydrate source for low-income urban consumers (Nweke, 1994). In Togo, cassava is the second important crop after maize, and the area of production is more than 60,000 hectares (DESA, 1998). Among pests and diseases that reduce the production of both roots and planting material of cassava, bacterial blight (CBB), caused by Xanthomonas campestris pv. manihotis (Xcm) (Berthet et Bondar) Dye is one of the major damaging diseases. Symptoms include angular leaf spots, blight, wilting and stem die-back after systemic infection. Yield losses range from 13% to 50% depending on the severity of infection (Wydra and Rudolph, 1999). The disease was reported for the first time in Togo in 1978 (Olympio, 1978). Later investigations showed that it was prevalent in the savanna and littoral ecozones and sporadically in the forest (Boher and Agbobli, 1992). Our studies aimed to survey the present status of the disease in the major ecological zones of Togo, the virulence of the pathogen and the resistance of cassava varieties.