Isolation distance as a phytosanitation option for cassava clean seed multiplication in Uganda

Cassava brown streak disease (CBSD) caused by cassava brown streak viruses and cassava mosaic disease (CMD) caused by different species of cassava mosaic geminiviruses (CMGs) are the two major viral diseases constraining cassava production in Uganda. Both diseases are spread through cuttings and are transmitted by whiteflies Bemisia tabaci. A number of phytosanitation strategies including isolation distances have been used to control these two cassava viral diseases. However, the minimum isolation distance has not been verified for effective virus control in the major cassava growing agro-ecologies and the quality of cassava seed remains a challenge in Uganda. In order to ensure that seed multipliers produce clean cassava seed in isolated fields to prevent infections before planting materials are provided to farmers, there is need to test different isolation distances in major cassava growing agro-ecological areas in order to establish the effective isolation distance for the management of CBSD and CMD as different areas in Uganda have different whitefly infestations and CBSD and CMD pressure. This review article presents a summary on virus status of cassava planting materials, major cassava viral disease prevalence at varying isolation distances and how phytosanitation strategies such as effective isolation distances can be an alternative option for clean seed multiplication for farmer preferred but susceptible cassava cultivars in Uganda. Key words: Cassava brown streak disease, cassava mosaic disease, clean seed planting materials, isolation distance, phytosanitation, Uganda