Advanced Study on Geographical Distribution and Incidence of Cassava Bacterial Blight (Manihot esculenta Crantz) Caused by Xanthomonas axonopodis pv. manihotis in Two Agro-ecological Zones of Côte d'Ivoire

Background and Objective: Cassava (Manihot esculenta Crantz) is the second largest food crop in
Côte d’Ivoire after yam. It is cultivated for its fleshy roots rich in starch and for the richness of its
leaves in minerals (calcium, phosphorus and iron). However, this crop is subject to numerous biotic
constraints of which one of the most formidable is bacterial blight caused by Xanthomonas
axonopodis pv. manihotis. In Côte d’Ivoire, no concrete study has been conducted on this emerging
disease with the aim of reducing its impact on the yield of tuberous roots of traditional and improved
varieties. The objective of this study is to study the distribution of bacterial blight on the one hand and
to assess the sensitivity of 8 varieties through an epidemiological study in two agro-ecological zones
of Côte d’Ivoire on the other hand.
Materials and Methods: Survey missions conducted in 2013 and 2014 have helped establish the
health map of the different cassava production zones, followed by an epidemiological study of the
disease with 8 cassava varieties of which four are improved, in two cassava production zones
(Yamoussoukro and Ferkéssédougou).
Results: The results showed that bacterial blight was observed in all agro-ecological zones with an
incidence ranging from 2.17-66.67%. As for the epidemiological study, it showed a contrast between
the two areas of study. The severity of the disease was very low in the dry season (December-March)
corresponding to the 7th until the 10th month of this study. Moreover, the rainy season contributed to
an expansion of the disease. Diarrassouba and Yacé (traditional varieties) and Bocou 1 (improved
variety) were the most susceptible to the disease.
Conclusion: Local varieties Akama and Dankwa were less tolerant to the disease than the improved
variety Bocou 1. The most important bacterial attack occurred during the rainy season and resulted in
mortalities in the most sensitive varieties. The data reveal an interest for the use of traditional varieties
Akama and Dankwa and improved varieties Yavo, Bocou 2 and Bocou 3 in the areas of high pressure
by cassava bacterial blight. A fight against this disease must be envisaged before it spreads to all
cassava cultivation zones in Côte d’Ivoire.