In-vitro techniques for elimination of viruses causing cassava mosaic disease and cassava brown streak disease

Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are the two most important viral diseases affecting cassava (Manihot esculenta) production in Uganda. The two diseases persist in the plant system causing yield losses and reduce quality of planting materials for the next planting. Cassava germplasm conservation efforts are still at its infancy and the current cassava seed systems is characterized by free exchange of cassava stakes among local communities, which promote the spread of CMD and CBSD. Farmerpreferred cassava varieties are particularly affected, and these need to be cleaned regularly. This paper highlights in-vitro techniques that have been developed and described for plant virus elimination including meristem tip culture, thermotherapy, and chemotherapy. The techniques may be used singly or in combination for effective virus elimination. The effectiveness of meristem tip culture, which is the most commonly used method for invitro virus elimination, critically depends on size of meristem. Nonetheless, virus type, position of meristem on the plant, and host plant species also determines efficiency of virus elimination and survival of explants. Thermotherapy and/or chemotherapy followed by meristem tip culture have been used to enhance virus elimination. The combination of thermotherapy followed by meristem tip culture minimizes difficulties associated with excision of small meristem size since thermotherapy allows for use of larger meristems. Further, chemotherapy followed by meristem tip culture increases efficiency of virus elimination but plant regeneration is low. High concentration of antiviral compounds may result in phytotoxicity and genetic mutations in plants. Together with application of sensitive virus detection and quantification methods before and after in-vitro treatment, a cheap combination of in-vitro techniques could be optimized for elimination of CMD and CBSD causing viruses.