Banana bunchy top virus in subSaharan Africa: investigations on virus distribution and diversity

Banana bunchy top virus (BBTV) was first reported from sub-Saharan Africa (SSA) from Democratic Republic of Congo (DRC) in the 1950s, has become invasive and spread into 11 countries in the region. To determine the potential threat of BBTV to the production of bananas and plantains (Musa spp.) in the sub-region, field surveys were conducted for the presence of banana bunchy top disease (BBTD) in the DRC, Angola, Cameroon, Gabon and Malawi. Using the DNA-S and DNA-R segments of the virus genome, the genetic diversity of BBTV isolates was also determined from these countries relative to virus isolates across the banana-growing regions around the world. The results established that BBTD is widely prevalent in all parts of DRC, Malawi, Angola and Gabon, in south and western part of Cameroon. Analysis of the nucleotide sequences of DNA-S and DNA-R indicate that BBTV isolates from these countries are genetically identical forming a unique clade within the ‘South Pacific’ phylogroup that includes isolates from Australia, Egypt, South Asia and South Pacific. These results imply that farmers’ traditional practice of transferring vegetative propagules within and between countries, together with virus spread by the widely prevalent banana aphid vector, Pentalonia nigronervosa, could have contributed to the geographic expansion of BBTV in SSA. The results provided a baseline to explore sanitary measures and other ‘clean’ plant programs for sustainable management of BBTV and its vector in regions where the disease has already been established and prevent the spread of the virus to as yet unaffected regions in SSA

Economic losses experienced by smallscale farmers in Malawi due to cassava brown streak virus disease

Cassava is an important root crop in Malawi. It is the second most important food crop after maize. It is grown throughout the country as a food security crop, sack/cash crop, and as a staple food crop along the Lake Malawi. Is is a staple for over 39 % of the country’s population. Farmers are not benefiting as much as they might from cassava because they are faced with a number of constraints. These include: - inherent low yielding and late maturing local cultivars - pests and diseases prevalent in the country - low promotion of good cultural practices. The major pests and diseases of cassava in Malawi are, cassava mosaic virus disease (CMD), cassava bacterial blight (CBB), cassava brown streak virus disease (CBSD), cassava green mite (CGM), cassava mealy bug (CM) and termites. The objective of this study was to determine the economic impact of CBSD on the farmers in Malawi where the disease is prevalent. The paper makes the following recommendations: - the cassava research organisations should mount urgent awareness campaigns of the disease and its management for both extension agents and farmers - the cassava research organisations should establish effective collaboration with the extension system on matters of proper cassava husbandry to effectively and efficiently control the disease - they should additionally carry out local collection exercises for cultivars that show CBSD disease resistance in the high disease pressure areas - there is an urgent need for cassava research and extension organisations to multiply cultivars and promising clones that have shown multiple disease resistance and that are widely accepted by farmers for distribution in the heavily affected areas - in collaboration with entrepreneurs, these organisations need to develop and strengthen sustainable seed multiplication and distribution systems as a way of assuring the provision of clean planting material