Epidemiological assessment of cassava mosaic disease in Burkina Faso

Abstract

Surveys were conducted in 2016 and 2017 across the main cassava-growing regions of Burkina Faso to assess the status of cassava mosaic disease (CMD) and to determine the virus strains causing the disease, using field observation and phylogenetic analysis. CMD incidence varied between regions and across years but was lowest in Hauts-Bassins (6.0%, 2016 and 5.4%, 2017) and highest in Centre-Sud (18.5%, 2016) and in Boucle du Mouhoun (51.7%, 2017). The lowest CMD severity was found in Est region (2.0) for both years and the highest in Sud-Ouest region (3.3, 2016) and Centre-Sud region (2.8, 2017). The CMD infection was primarily associated with contaminated cuttings in all regions except in Hauts-Bassins, where whitefly-borne infection was higher than cuttings-borne infection in 2016. PCR screening of 687 samples coupled with sequence analysis revealed the presence of African cassava mosaic-like (ACMV-like) viruses and East African cassava mosaic-like (EACMV-like) viruses as single infections at 79.5% and 1.1%, respectively. Co-infections of ACMV-like and EACMV-like viruses were detected in 19.4% of the tested samples. In addition, 86.7% of the samples positive for EACMV-like virus were found to be positive for East African cassava mosaic Cameroon virus (EACMCMV). Phylogenetic analysis revealed the segregation of cassava mosaic geminiviruses (CMGs) from Burkina Faso into three clades specific to ACMV, African cassava mosaic Burkina Faso virus (ACMBFV), and EACMCMV, confirming the presence of these viruses. The results of this study show that EACMCMV occurrence may be more prevalent in Burkina Faso than previously thought.

Keywords: African cassava mosaic virus (ACMV); East African cassava mosaic Cameroon virus (EACMCMV); cassava mosaic geminiviruses; geminiviruses characterization; geminiviruses distribution.

FIGURE 1

Map of Burkina Faso showing the regions and localities where surveys were done in 2016 and 2017 [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Symptoms of cassava mosaic disease observed on infected cassava plants during the surveys, using a scale from 1 (no symptoms) to 5 (very severe symptoms). (a) = 1, (b) = 2, (c) = 3, (d) = 4, (e) = 5 [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Epidemiological assessment of cassava mosaic disease (CMD) in Burkina Faso. (a) CMD incidence (percentage of plants with symptoms). (b) Severity of CMD (mean CMD severity score of plants with symptoms). (c) Proportion of plants with different CMD severity scores in 2016 and 2017. (d) Mean whitefly counts in 2016 and 2017. (e) Proportion of plants with symptoms infected by cutting or whitefly in 2016 and 2017. The bars represent the standard error. Bars sharing the same lower case letters are not significantly different between regions in 2016 and those sharing the same upper case letters are not significantly different between regions in 2017 [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

Maximum‐likelihood phylogenetic tree obtained from alignment of partial nucleotide sequences of coat protein (CP) genes of African cassava mosaic‐like viruses (ACMV‐like) and East African cassava mosaic‐like viruses (EACMV‐like). The names of the sequences characterized in this study are in red. The horizontal scale indicates the genetic distance [Colour figure can be viewed at wileyonlinelibrary.com]