Genetic variability within the coat protein gene of Grapevine fanleaf virus isolates from South Africa and the evaluation of RT-PCR, DAS-ELISA and ImmunoStrips as virus diagnostic assays.

Grapevine fanleaf virus (GFLV) is responsible for severe fanleaf degeneration in grapevines of all major wine producing regions of the world, including South Africa. In order to successfully control the spread of the virus, specific and reliable diagnostic assays are necessary. The genetic variability of 12 GFLV isolates recovered from naturally infected grapevine plants in the Western Cape region of South Africa were characterised. These samples were subjected to RNA extraction, RT-PCR analysis and sequencing of the coat protein gene (2CCP). Sequence identities between different GFLV isolates from South Africa were between 86-99% and 94-99% at the nucleotide and amino acid levels, respectively. Phylogenetic analysis based on the 2CCP gene sequences showed that the South African isolates form two distinct clades or sub-populations. The specificity and sensitivity of three diagnostic techniques (rapid-direct-one-tube-RT-PCR, DAS-ELISA and ImmunoStrips) for the detection of GFLV were analysed to determine the appropriate diagnostic assay for virus infection. Rapid-direct-one-tube-RT-PCR was found to be the most reliable technique for detection. This is the first report on sequence analysis of full-length 2CCP gene cDNA clones of GFLV isolates from South Africa.