Multiplex RT-PCR-ELISA compared with bioassay for the detection of four apple viruses

A sensitive and reliable multiplex RT-PCR-ELISA technique for the detection of Apple chlorotic leaf spot virus, Apple stem pitting virus, Apple mosaic virus and Apple stem grooving virus was developed. This technique is compared with the method used commonly for indexing by woody indicators, which is time consuming and expensive. For the RT-PCR-ELISA technique, the amplified products were labeled with digoxigenin during the RT-PCR by incorporation of a digoxigenin labeled primer. After hybridization of the PCR products to specific capture oligonucleotides, which were bound covalently to the surface of NucleoLink strips, anti-digoxigenin antibodies were used for detection. More than 100 samples were tested in parallel by indexing and multiplex-RT-PCR-ELISA. All infections detected by woody indicators were also detected by multiplex RT-PCR-ELISA. Furthermore, additional infections were only found by multiplex RT-PCR-ELISA. The colourimetric detection of multiplex-RT-PCR products was at least as sensitive and sometimes slightly more sensitive than detection by gel electrophoresis. The results show that this molecular technique is more reliable for the detection of the above mentioned apple viruses than indexing by woody indicators, thereby helping to reduce cost and time during the certification of plant material.