Abstract

Cassava mosaic disease (CMD) caused by cassava begomoviruses is the major constraint to cassava production in Ghana. The disease is known to cause reduction in root yield. To ascertain the distribution of viruses causing CMD, 95 diseased cassava samples were collected in two agroecological zones of Ghana-Deciduous Forest zone and the Transitional zone. On a scale of 1-5, CMD severity was scored. Mean CMD severity score was 2.9, however there was no significant difference (p > 0.05) between the zones. Averagely, CMD score of > 2.8 in 71% of farms visited was recorded. Polymerase chain reaction (PCR) and rolling circle amplification (RCA) were employed for virus identification. PCR revealed that African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV) and mixed infections were prevalent in both zones. EACMV-Cameroon strain was also identified to be common within these zones. The transitional zone had the highest percentage of CMD infection. Unamplified samples from PCR were amplified using rolling circle amplification (RCA) technique. Amplification and characterisation of complete genome sequences of two isolates were carried out. The complete genome of 2780 nucleotides from samples showed a high similarity to African cassava mosaic virus-Ghana (ACMV-GH). Sequences clustered with ACMV-Ivory Coast, ACMV Nigeria-Ogo, ACMV-BF, ACMV-UG having > 96% identity. This shows the close relation that exists amongst the ACMV strains in Africa. These findings highlight the need for a continuous survey of CMD to help manage the disease in the country.

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