Prevalence of Cassava Mosaic Geminiviruses in the Volta Region of Ghana

Cassava Mosaic Disease (CMD), caused by Cassava Mosaic Geminiviruses and transmitted by Bemisia tabaci, is a major constraint to cassava production in Africa. The objective of the study is to determine the prevalence, spatial distribution, and diversity of Cassava Mosaic Geminiviruses in the Volta Region of Ghana.

A field survey was conducted between June and August 2019 to ascertain the prevalence, spatial distribution, and diversity of CMGs in the Volta Region. A total of five farms were selected from each of the three communities within each of the six districts, resulting in a total of 90 farms. From each farm, 30 plants (25 symptomatic and 5 asymptomatic) were randomly sampled, ensuring a minimum distance of 30 km between farms. Data were collected on disease incidence, disease severity, and whitefly population across all sites. Incidence and whitefly data were appropriately transformed prior to analysis, while severity scores were calculated. The resulting data were analysed using Analysis of Variance (ANOVA) in GenStat statistical software, version 11.

The incidence and severity of CMD were high, ranging from 77.20 ± 1.64 in Hohoe to 96.67 ± 0.23 in Krachi Nchumuru, and from 2.93 in Adaklu to 4.37 in Hohoe, respectively. Whitefly populations were generally high, with Krachi Nchumuru and Adaklu recording 10.01 ± 0.22 and 5.93 ± 0.25, respectively.

Pearson’s coefficient of correlation indicated a strong positive significant correlation (r=0.719; p<0.05) between whitefly population and incidence, and a significant weak negative correlation (r=-0.177; p<0.05) between rainfall and disease severity and temperature. A higher percentage (more than half) of leaf samples were co-infected with ACMV and EACMV than either species alone in all six districts surveyed.

The severe CMD prevalence in the Volta Region, compounded by whiteflies, susceptible varieties, and high ACMV–EACMV co-infections, highlights the urgency of resistant planting materials, farmer awareness, and enhanced monitoring to curb disease spread and prevent the emergence of new CMG species.