A quantified approach to projecting losses caused by Fusarium wilt Tropical race 4

Fusarium oxysporum f. sp. cubense (Foc) Tropical race 4 (TR4) has been characterized as primarily a threat to export 'Cavendish' bananas, although others highlight the potential menace to smallholder banana livelihoods globally. To date, no systematic assessment or approach to estimate the risk of introduction, the rate of internal spread and the estimated production losses by country have been done. As part of a study to assess the economic returns to different banana research investments through the CGIAR Research Program, Roots, Tubers and Bananas (CRP RTB), we formulated an approach to estimate production losses resulting from TR4 spread by country over a 25-year period. Factors linked to the time lag for TR4 to reach a country were identified from risk analyses conducted in Africa, Latin America and Asia. These include factors such as the importance of mono-cropped 'Cavendish', global banana traffic to and from a country, quality of borders and internal plant quarantine measures, and land and other links to countries where TR4 is currently present. The rate of internal spread was rated based on three factors: quality of internal quarantine measures, importance of 'Cavendish', and importance of banana for research investment and public policy. The higher the aggregated score for a country, the faster the spread and thus the higher the expected loss of banana production due to TR4 with differentiated losses depending on cultivar types. Loss of production was proposed between 1 and 8% of area planted during the first 5 years after detection, depending on cultivar group and the country score. Assuming exponential growth, in each successive 5-year period after first detection, the spread rate was calculated to increase 50%. Summing up over the 29 countries included in the analysis, an estimated 1.70 million ha of banana production area will be affected by 2040. Lowering the spread rate increase from 50 to 25% decreased estimated global production area affected to 1.26 million ha. This initial assessment will serve to elicit feedback from the global banana community on parameter estimates and to test the robustness of the calculations to estimate losses.