The use of citrus tristeza virus (CTV) containing a green fluorescent protein gene as a tool to evaluate resistance/tolerance of transgenic citrus plants

The T36 strain of citrus tristeza virus (CTV) expressing green fluorescent protein gene (CTV-GFP) was used to detect replication of CTV in wild-type (WT) ‘Hamlin' sweet orange plants and those transformed with the use of Agrobacterium tumefaciens strain harboring a binary vector with a coat protein gene from either T36 or T30 isolate of CTV. Soil-adapted WT and transgenic plants were challenged with CTV by grafting shoots from CTV-GFP infected plants. None of the transgenic plants appeared to be able to inhibit CTV replication as CTV-associated GFP fluorescence in all of them was detected by fluorescent microscopy. For the purpose of comparison of two different methods, CTV multiplication in transgenic plants was also examined by enzyme-linked immunosorbent assay (ELISA) assays. GFP-labeled CTV represents a useful tool for estimation of susceptibility of citrus cultivars or transgenic lines to CTV infection. This method using CTV-GFP is simpler, cheaper and less time-consuming than ELISA.