Incidence of Cassava Viral Diseases and First Identification of East African cassava mosaic virus and Indian cassava mosaic virus by PCR in Cassava (Manihot esculenta Crantz) Fields in Togo

Cassava is infected by numerous Begomoviruses in Africa and India that cause devastating losses to poor farmers. In order to identify viruses responsible for the disease and characterize them, surveys were conducted in all cassava production zones in Togo. The symptom severity of these viral diseases was recorded. Foliar samples from cassava and other infected plants were collected and analysed by PCR. The results obtained reveal that the severity of the symptoms varies from one locality to another, some more severely cassava infected plants than others. The percentage of the cassava plants presenting typical mosaic symptoms varies from 55 to 85% and the percentage of cassava plants severely infected (score 4 or 5) varies from 4.9 to 36%. Molecular analyses by PCR of the viral DNA extracted from the diseased samples using specific primers revealed for the first time that African cassava mosaic virus (ACMV) is not the only Begomovirus responsible of cassava mosaic disease in Togo, but two other Begomoviruses, East African cassava mosaic virus (EACMV) and Indian cassava mosaic virus (ICMV) are present in Togo. Their incidence rates are 73.59, 44.62 and 4.01%, respectively for ACMV, EACMV and ICMV. Mixed infections were also identified at the rates of 39.45% in the case of (ACMV + EACMV), 1.72% for ACMV + ICMV and 1.29% when the three viruses were combined (ACMV + EACMV + ICMV). (Resume d'auteur)