Risk-assessment studies of virus-resistant transgenic plants (VRTPs)
focussing on recombination of a plant virus with a transgenic sequence of a
different virus should include a comparison of recombination frequencies
between viruses in double-infected non-transgenic plants with those observed
in singly infected transgenic plants to estimate recombination incidence in
VRTPs. In this study, the occurrence of recombination events was
investigated in non-transgenic plants double-infected with two different
potyviruses, as well as in potyviral genomes in singly infected transgenic
plants expressing potyvirus sequences. Different potyviruses, namely Potato virus A (PVA),
Tobacco vein mottling virus (TVMV), two strains of Potato virus Y (PVY-O, PVY-H) and two strains of Plum pox virus (PPV-NAT,
PPV-SK68), were used in three combinations for double infection of a common
host. Furthermore, transgenic plants expressing either potyviral coat
protein (CP), helicase (CI) or polymerase (NIb) coding sequences
(PPV-NAT-CP, PVY-CI, PVY-NIb) were singly-infected with a heterologous
potyvirus, which was not targeted by the respective transgenic resistance.
To identify recombinant potyviral sequences, a sensitive RT-PCR was
developed to detect up to one recombinant molecule out of 106 parental
molecules. In 304 mixed infected non-transgenic plants, 92 mixed and 164 single infected transgenic plants screened for recombinant sequences no
recombinant potyviral sequence was found. These results indicate that
recombination events between different potyviruses in mixed infections and
between a potyvirus infecting a potyvirus-resistant transgenic plant are
likely to be very infrequent.