However, a knowledge of the molecular biology of viruses enables us to construct synthetic resistance genes and to transfer these into plants by genetic engineering procedures. To this end, we are characterising certain important plant viruses and using this information in the construction, glasshouse testing and field evaluation of synthetic resistance genes in pastures. In addition to providing novel approaches to carbon partitioning, the problems of virus, nematode and fungal pathogen resistances, genetic engineering offers the means of introducing other useful traits into agronomically important plants. Several approaches, including altering carbon and sulfur sinks, are being explored to improve the value of crop and pasture plants for animal nutrition. Weeds in legume-based pastures can greatly limit productivity by reducing plant quality for animal nutrition and by reducing the level of fixed nitrogen for the subsequent cropping phases.
Subterranean clover has partial tolerance to the herbicide bromoxynil.
This partial tolerance can be enhanced by introducing into subterranean clover, a gene encoding an enzyme capable of de-toxifying the herbicide. This raises the prospect of controlling broad leaf weeds in subterranean clover-based pastures. Bloat safety for forage legumes is also being pursued by using genetic engineering to increase the levels of condensed tannins in leaves. Bloat results when animals feed on pastures with a high proportion of protein in the soft-celled leaves of plants such as lucerne and white clover. Bloat is responsible for substantial losses to the meat and dairy industries.