Four years assessment of Cassava Bacterial Blight expression according to weather conditions in Côte d’Ivoire

Abstract

Cassava growth in Cote d’Ivoire is affected by the variation in weather conditions and various pests and diseases. Cassava Bacterial Blight is a particularly destructive disease influenced by weather conditions which can lead to 100% yield loss. In order to provide sustainable control strategies, it is essential to understand the occurrence and the behaviour of the disease in the different ecological zones in Cote d’Ivoire. Surveys were carried out in cassava fields from 2014 to 2017 in the seven Ivorian agro-ecological zones. These fields were assessed for the disease presence/absence, the severity index (SI) and the disease incidence (DI). Weather data were provided by weather stations in Cote d’Ivoire. The results of this study showed that the disease was present in mainly the agro-ecological zones 1, 2, 3 and 4 representing the higher yield potential zones of cassava production. Disease expression was variable depending on the years and the prevalent weather conditions in each agro-ecological zone. The high SI and DI were found in the agro-ecological zones 1, 4 and 6. The disease was able to reach rates of 100% in many zones for both SI and DI with dieback incidence mainly in the agro-ecological 1, 4 and 6 zones under unfavourable (low rainfall, RH, NRD) and favourable conditions. It is therefore urgent to implement control strategies such as such as the integration of new cassava varieties, screening under different agro-ecological zones and improvement of varieties in order to provide resistant varieties to the farmers.