Reinfection Dynamics of Disease-Free Cassava Plants in Three Agroecological Regions of Côte d’Ivoire

Abstract

Cassava mosaic disease (CMD) is caused by begomoviruses and can result in yield losses of up to 90% in susceptible varieties. Using disease-free planting material from in vitro cultures is one of the most effective ways of controlling this disease. A CMD epidemi- ological assessment was conducted in fields established with disease-free plantlets in Bouaké, Dabou, and Man, selected for their contrasting agroecological and CMD preva- lence conditions. Virus and whitefly species characterisation was performed using PCR and sequencing. CMD incidence and severity were lowest at the Man site and highest at the Dabou site. Although whitefly abundance was relatively low at the Man and Bouaké sites compared to the Dabou site, they were a significant factor in the spread of the disease. While all resistant varieties remained asymptomatic, susceptible and tolerant varieties became infected, and some tolerant varieties were able to recover from the disease. Molec- ular analyses revealed the presence of two viral species: Begomovirus manihotis (ACMV) and Begomovirus manihotiscameroonense (EACMCMV). No viral infection was detected 4 weeks after planting (WAP). Cases of single infection and double infection were observed at 12 and 20 WAP. Also, no double infections were found at the Man site, in contrast to the Bouaké site (12 WAP: 2.36%) and Dabou site (12 WAP: 2.59%; 20 WAP: 5.76%). EACMCMV was found in a single infection in Bouaké (12 WAP: 1.39%) and Man (20 WAP: 0.66%). The whitefly species Bemisia tabaci and Bemisia afer were most commonly found feeding on all cassava varieties. A high diversity of whitefly species was observed in Bouaké and Dabou compared to Man. Furthermore, the Bemisia tabaci species identified in this study was found to be able to transmit ACMV and EACMCMV viruses. These highlights would contribute to improving CMD management and control strategies.