Transmission and distribution of cassava brown streak virus disease in cassava growing areas of Kenya
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Objectives: To determine the incidence and distribution of cassava brown streak disease (CBSD) in relation to Bemisia tabaci populations in Central, Eastern, Nyanza and Western provinces of Kenya and investigate the ability of 4 cassava pests to transmit cassava brown streak virus (CBSV). Methodology and results: A multistage sampling survey was conducted from November 2006 to April 2007 to determine CBSD incidence and distribution in relation to B. tabaci populations in major non-coastal cassava growing areas of Kenya. In a separate study, adults of test insects were allowed 48 hours acquisition feeding period on CBSV infected cassava plants in cages before being transferred to uninfected plants. CBSD was present at high incidences in western Kenya (38-93%) but was not detected in Central and Eastern provinces. Large B. tabaci populations observed in western Kenya were significantly and positively correlated to CBSD incidence indicating a considerable contribution of the whiteflies to the spread of CBSD. Transmission of CBSV by B. tabaci occurred at 27.8%, a confirmation and additional evidence that this whitefly species is a vector of CBSV. Conclusion and application: This report provides evidence that CBSD is no longer restricted in distribution to the coastal lowlands of Kenya. The study further confirms that CBSD is spread by B. tabaci and therefore its control should be included in the overall management of CBSD. These findings increase the understanding of CBSD epidemiology.