Testing genetically engineered potato, producing the lectins GNA and Con A, on non-target soil organisms and processes

1. Two lectins, concanavalin A (Con A) and Galanthus nivalis agglutinin (GN A), have anti-feedant properties that suggest a potential for the control o f invertebrate pests of plants. We tested potato plants genetically enginee red to produce each of these lectins constitutively, as well as the purifie d lectins, for possible non-target effects. 2. Laboratory studies with soil bacterial communities and a ciliate protozo an could detect no direct effect of either lectin over a range of concentra tions. There was a significant inhibition in the host-finding response of a bacterial-feeding nematode when Con A or GNA was present in the medium at 0.5-50 mu g ml(-1.) 3. A number of GNA- and Con A-producing potato lines had no detectable effe cts on the rhizosphere microbial and microfaunal populations when examined in pot trials. The incorporation of leaves from transgenic plants into soil reduced protozoan populations significantly, but there was no subsequent e ffect on the decomposition of added cotton strips. 4. Controlled field-release experiments demonstrated that, although GNA-pro ducing potato lines consistently altered the physiological profile of the r hizosphere microbial community at harvest, the effect did not persist from one season to the next over a trial period of two field seasons. There was no significant effect of the best performing GNA line on the development of a subsequent barley crop. 5. A single Con A-producing line was tested in a controlled field-release. The only significant effects were transient reductions of c. 40% in soil pr otozoan populations and of c. 10% in potential microbial activity.