Phenotypic and molecular screening of cassava (Manihot esculentum Crantz) genotypes for resistance to cassava mosaic disease

Cassava mosaic disease (CMD), caused by cassava mosaic geminivirus (CMG) is the most-important disease threatening production of cassava (Manihot esculenta) in Ghana. The disease is best managed through host-plant resistance. The study was conducted to assess resistance of 38 cassava genotypes to CMD, determine the associated resistance gene, and to identify the strains of CMG infecting cassava in Ghana. Both morphological and molecular markers were used to screen 38 cassava accessions against CMG infection. Morphological studies revealed one genotype (Capevars) as highly resistant whilst three others (Adehye, Nkabom and KW085) were tolerant, showing mild symptoms. PCR analyses using strain specific primers, however, detected the virus in all the three tolerant genotypes, but absent in Capevars. However, the dominant CMD resistance gene, CMD2, was detected in both the resistant and the tolerant genotypes. Apart from Capevars, the other 37 cassava genotypes were infected by, at least, one of the four ACMV variants of ACMV1, ACMV2, ACMV-AL and ACMV3. It is, therefore, concluded that field screening for CMD resistance, should integrate phenotypic evaluation and detection of the virus.  Key words: Cassava, African cassava mosaic virus, simple sequence repeats, resistance.