Assessment of nutritional characteristics of virus-resistant transgenic white clover (Trifolium repens L.) grown under field and glasshouse conditions

Abstract

White clover (Trifolium repens L.) is an important pasture legume in temperate areas throughout the world, providing fodder for grazing animals and improving soil fertility via symbiotic nitrogen fixation. However, the persistence and stress tolerance of white clover are affected by a number of viruses including alfalfa mosaic virus. Transgenic white clover plants with ectopic expression of the alfalfa mosaic virus coat protein were resistant to the virus under field and greenhouse conditions. With all genetic modifications of major consequence, there is the possibility of unintended effects on forage quality and natural toxicant levels. In this paper, we describe the evaluation of a range of parameters related to the nutritive value of white clover herbage to grazing animals and a suite of naturally occurring secondary metabolites that have the potential to be natural toxicants in transgenic white clover plants and wild-type control plants with a similar genetic background. Samples were collected from plants grown under both field and glasshouse conditions. Several commercial cultivars were included for comparison. Although there was plant-to-plant variation, as expected from an obligate outcrossing species, there were no significant differences in the range of this variation between transgenic and wild-type plants. Furthermore, no consistent significant differences were found between groups of transgenic and wild-type plants from the same generation, when mean nutritional parameters (crude protein, in vitro dry matter digestibility, neutral detergent fibre and water-soluble carbohydrates) and natural toxicants (cyanogenic glucosides, phytoestrogens and saponins) were compared.