Fighting a two-pronged attack on African bananas
Among the many diseases that affect bananas and plantains in Africa, the two greatest threats are Banana Xanthomonas Wilt (BXW) and Banana Bunchy Top Disease (BBTD). Combined, these diseases have the potential to wipe out these economically- and food security-vital crops from the continent. Their rapid spread in recent years has alarm bells ringing in banana-producing countries across Africa Hüpfburgen.
BXW, which in the past had only been prevalent in Ethiopia, has been highly active in East Africa this past decade. On the other hand, BBTD, which was first reported in the 1920s and then the 1960s in Egypt and DR Congo, respectively, has been spreading rapidly in the East African highlands and in Central and Southern Africa.
In the face of this two-pronged threat, we have been actively engaged in a number of complementary disease-management research. These include developing specific diagnostic assays, initiating regional surveillance to map current disease distribution and future spread, developing management tools to minimize establishment, spread, and impact, and working on host-plant resistance through germplasm screening and biotechnology approaches.
As the BXW pathogen is closely related to other Xanthomonas pathogens that affect maize, sorghum, and sugarcane, we, together with advanced laboratories in the USA, developed a highly specific assay to identify the banana variant using genomic tools. We also developed a sensitive assay for the banana bunchy top virus (BBTV), the causal agent of BBTD.
These two assays are now being used for verification of suspected BXW and BBTD cases in East and southern Africa in cooperation with national and private sector partners.
The development of sensitive diagnostics for BXW and BBTD permits epidemiological studies in plants that do not show symptoms during the latent period, rapid deployment of control measures, and effective detection of the pathogens by quarantine officers along borders.
We also conducted surveys with national partners in southern and Central Africa to map the extent of spread of BBTV, and to determine the abundance and distribution of the banana aphid, the only known insect vector of BBTV.
We recognize that insects play an important role in the spread of banana diseases, so we initiated studies on host-plant resistance to the banana aphid that spreads BBTV. We also plan to explore for natural enemies of the banana aphid in its putative area of origin in 2010. In Malawi, we established a field trial of various banana cultivars to study host reaction to BBTV and assess virus concentration.
Many insects have been implicated in the medium-distance, farm-to-farm spread of BXW. To help us develop management guidelines, we have been conducting studies in an isolated and controlled site in a forest reserve to further understand how insects spread the BXW pathogen.
Together with the Southern Africa Development Community, the Association for Strengthening Agricultural Research in Eastern and Central Africa, FAO, Bioversity International, and other partners, we co-organized an international workshop in Arusha, Tanzania in August to integrate recent information on these diseases and develop control strategies.
The workshop recommended measures to slow the spread of these diseases into new regions and offset their impact in already-affected areas. These included large-scale awareness and surveillance campaigns, community-level cooperative actions, establishment of reporting, communication, and monitoring systems, improved “seed” systems, development of national contingency plans, and long-term programs for eradication and/or management of BXW and BBTD.
A follow-up meeting in 2010 is being planned to establish the framework of a region-wide disease-management and production strategy.