Cassava mosaic disease incidence and severity and whitefly vector distribution in Gabon

Abstract

Cassava mosaic disease (CMD) is a major constraint to cassava (Manihot esculenta Crantz) production in sub-Saharan Africa. The objective of this study was to gain insights into the epidemiology of CMD in cassava production systems in Gabon. An epidemiological survey was conducted throughout Gabon from October 2020 to May 2021 to evaluate the epidemiology of cassava mosaic disease (CMD) in cassava farms. A phytosanitary diagnosis was conducted at each farm, using the harmonised and unified WAVE protocol to assess the incidence and severity of CMD and the abundance of its whitefly vector. All data collected were recorded using WAVE’s mobile application and uploaded into the WAVE Cube data system. The results showed that CMD was present in all farms surveyed (n = 227; 100%), but with a variable incidence rate. At national level, the incidence of CMD was high, with an average of 64.29%. However, incidence differed among regions with 82.22 and 79.20% for Ogooue-Maritime and Nyanga; respectively, but only 40.42% for Estuaire. Woleu-Ntem had the highest mean severity (3.47) and Ogooue-Maritime the lowest (2.64). Overall, incidence and severity differed significantly among regions (P< 0.05). The average abundance was 2.58 whiteflies per plant (w/p), varying between 1.06 (Nyanga) and 5.25 w/p (Estuaire). The use of infected cuttings was the main mode of CMD spread (62.67%). These results highlight the need to identify the viruses responsible for the observed cases of CMD, to sanitise cultivated plant material, and to implement a CMD control strategy in Gabon.