1.11.41
POTENTIAL RISKS ASSOCIATED WITH THE RELEASE OF TRANSGENIC CROPS EXPRESSING LUTEOVIRUS GENE SEQUENCES

HG SMITH1, N PATRON1, MA MAYO2, H BARKER2 and MS LINEY2

1IACR-Broom's Barn, Higham, Bury St Edmunds 1P28 6NP, UK; 2Scottish Crop Research Institute, Dundee, DD2 5DA, UK

Background and objectives
Control of virus yellows in sugar beet and potato leafroll in potatoes is currently based on the use of chemicals and/or virus-free planting stock, although resistant varieties could provide a more environmentally acceptable alternative. In addition to using conventional breeding methods to produce plants with inherited resistance to viruses, considerable interest has focused on protecting plants from virus attack by introducing cDNA to virus genomic sequences into the host-plant DNA by transformation. However, there are concerns that recombination will occur between the genome of an invading virus and transcript RNA from the virus sequence DNA of the transgenic plant. This might result in new disease problems, such as the creation of new viruses with altered host ranges and vector specificities.

In work to assess this possibility, we are investigating (i) the frequency with which mixed infections with the luteoviruses beet mild yellowing virus (BMYV), beet western yellows virus (BWYV) and potato leafroll virus (PLRV) and their strains occur in crop plants and weeds, and (ii) the frequency of recombination among these viruses in nature and in experimentally infected hosts.

Materials and methods
The incidences were measured of natural virus infection among the weeds commonly found growing in proximity to arable crops such as sugar beet, oilseed rape and potatoes. Samples were assayed by using ELISA to screen for BMYV, BWYV and PLRV as well as a number of other viruses. Experimental transmissions of PLRV were made using Myzus persicae from colonies established on Physalis floridana infected with a Scottish isolate of PLRV. Aphids were fed on young test plants for ca 18 h and then killed by fumigation.

Results and conclusions
In September 1996, 1020 weeds were collected from 26 arable crops in Lincolnshire, Suffolk and Norfolk. Of all weeds tested, 20% reacted positively in ELISA with antisera to at least one virus and 3% reacted with antisera to more than one virus. Most positive samples (17% of the samples tested) contained a luteovirus and 1% contained more than one luteovirus.

In laboratory experiments with aphids carrying PLRV, we detected infection of weed species, including some not known previously to be hosts of PLRV.

Results from this project will ultimately be used by the Ministry of Agriculture, Fisheries and Foods in assessing the potential risks to the environment associated with growing genetically engineered resistant varieties of sugar beet.

This work is financed by the Ministry of Agriculture, Fisheries and Foods and the Sugar Beet Research and Education Fund. IACR receives grant-aided support from the Biotechnology and Biological Sciences Research Council of the United Kingdom. The Scottish Crop Research Institute (SCRI) receives a grant-in-aid from the Scottish Office Agriculture, Environment and Fisheries Department (SOAEFD).