BEGOMOVIRUSES INFECTING CASSAVA AND WHITEFLY (Bemisia tabaci Gennadius) POPULATION IN TARABA STATE, NIGERIA

Abstract

Begomoviruses infecting cassava are transmitted by whitefly and by the use of infected cuttings. They constitute major biotic constraints to cassava productivity in Nigeria. This study reports the occurrence and distribution of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) infecting cassava in Taraba State, Nigeria during 2015 growing season. Twenty-seven (27) cassava fields were sampled at interval of 10 km from five Local Government Areas (LGAs) of the State. Eighty-one leaf samples from symptomatic and asymptomatic cassava plants were collected and tested for ACMV and EACMV using polymerase chain reaction (PCR). The laboratory analysis revealed the incidence of ACMV and EACMV in the State with significant (p = 0.05) variation in distribution. Gassol had the higher incidence of both ACMV and EACMV (41.7 %) and (16.7 %) respectively followed by Wukari (ACMV 33.3 %) and Ardo-kola (EACMV 14.29 %) while in Zing both ACMV and EACMV were not detected and EACMV was not detected in Wukari. Cassava mosaic disease (CMD) incidence was higher in Wukari (93.3 %) followed by Gassol (47.0 %) while Zing had CMD incidence of 0 %. Symptom severity was statistically mild but Wukari recorded highest mean (2.7) followed by Gassol (2.04) and lowest in Zing (1.0). Adult whitefly populations were generally low, the highest mean (2.0) was recorded in Gassol and Zing and lowest in Wukari (0.0). The CMD source of infection was mainly by the use of infected cuttings than by the whitefly vector transmission. These findings revealed that whitefly, the established insect vector, is not responsible for the spread of CMD in Taraba State but rather by the use of infected cassava cuttings by farmers. The findings of this study also revealed the importance of using virus-free cassava cuttings as planting materials to mitigate the spread of cassava begomoviruses in the State and country at large.