Response of Selected Cassava Varieties to the Incidence and Severity of Cassava Brown Streak Disease in Tanzania

Cassava brown streak virus disease (CBSD) has been a serious and most damaging disease in cassava crop throughout the East, Central and Southern part of Africa. Several cassava varieties invariably respond to the disease, but the effect of the disease on affected varieties was not known. The current study was conducted to assess the ability of some farmer-preferred CBSD-affected varieties to withstand the disease. Field experiments were conducted at Kibaha Agricultural Research station from 2006 to 2008. The inherent variety characteristics influenced the incidence and severity levels of CBSD in the test plants. Leaf and stem CBSD incidences and severities, root weight and number of whiteflies (vectors) were significantly (P<0.001) related to the individual variety. Varieties Albert, Cheupe, Kibaha and Nachinyaya were seriously affected. The CBSD incidences and severities in these varieties increased with plant age, with highest disease records starting at nine to twelve months after planting. Dual infections of CBSD and CMD were recorded in four (Cheupe, Kibaha, Namikonga and Nachinyaya) of the five test varieties. Namikonga was proven to be resistant to CBSD. The correlation analysis suggested a significantly positive relationship between the perceived disease vector, Bemisia tabaci and the incidence and severities of CBSD and CMD. It was concluded that different varieties responds differently to CBSD and the disease severity increases with plant age.