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 is 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 occuring 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.

Determination of Phytoestrogen Content in Fresh-Cut Legume Forage

“…In recent years, phytoestrogens have been investigated by Wu et al [ 16 ], Lucas et al [ 5 ] and Barreira et al [ 17 ]. These works are primarily directed at evaluating such traditional legume species as red clover and alfalfa.…”

“…Biochanin A and formononetin are methylated precursors occurring in the human body and probably are metabolized in the colon on the practically most important phytoestrogens genistein (4′,5,7-trihydroxyisoflavone) and daidzin (4′,7-dihydroxyisoflavone) [ 1 ]. Some sources claim that formononetin in ruminants is estrogenically more active than is genistein degraded to daidzein and then metabolized to equol, which is a weak estrogenic compound ( Figure 1 ) [ 5 ]. Although formononetin itself shows no estrogenic activity, its metabolite causes so-called clover disease occurring mainly in small ruminants (especially sheep).…”

“…Coumestrol occurs in soybean, red clover and alfalfa, among other plants [ 7 ]. The occurrence of coumestrol may be evoked by leaf disease [ 5 ]. In New Zealand, a reduction of reproductive performance was observed in ewes on pastures including some alfalfa in the stand.…”

“…The available sources indicate that phytoestrogen values exceeding 1% of dry matter (DM) are associated with reproductive disorders in animals. It is reported that phytoestrogen values remain below that threshold in white clover [ 5 ]. The content of isoflavonoids is said to range from 1% to 2% of DM in red clover [ 1 ].…”

Considerations for Managing Agricultural Co-Existence between Transgenic and Non-Transgenic Cultivars of Outcrossing Perennial Forage Plants in Dairy Pastures

“…In this study there was no difference in the nutritional characteristics (crude protein, in vitro dry matter digestibility, neutral detergent fibre, and water soluble carbohydrates) and anti-nutritional characteristics (cyanogenic glucosides, phytoestrogens, and saponins) were compared for two conventional white clover cultivars (Mink, Grasslands Sustain) and their GM AMV resistant derivatives when grown under field or glasshouse conditions [34].…”