Assessing the Risk Posed by Transgenic Virus-Resistant Trifolium Repens to Native Grasslands in Southeast Australia

In Australia, comprehensive environmental risk assessments must be performed on transgenic plants (GMOs) prior to their commercial release. A key element is the determination of whether the release of a particular GMO poses any weediness threat to the environment or other agricultural systems, which can occur by means of direct invasion or by introgression of transgenes into wild populations of the same or closely related species. For transgenic pasture plants this question could be of added importance because many of these species have been selected for traits encouraging long-term persistence and competitiveness in complex plant communities (Godfree et al., 2004a). In situations where native vegetation is of high conservation value, such as Australia, the potential for transgenic pasture plants to invade native plant communities must therefore be quantified and analysed within a rigorous risk assessment framework. Over the past three years we have investigated the level of risk posed by transgenic virus-resistant (VR) Trifolium repens (white clover) to native grasslands and woodlands in the subalpine and montane regions of southeastern Australia. We have focused on identifying the viruses present in white clover populations in the subalpine zone, on determining the floristic composition of the communities that are most at risk, and on quantifying the likely selective advantage of VR T. repens in these environments

Severe effects of long-term drought on calcareous grassland seed banks

Climate change models project shifts in precipitation patterns at regional and global scales. Increases in dry areas and the occurrence of drought predicted in future scenarios are likely to threaten grassland ecosystems. Calcareous grassland seed banks have proven to be resistant to short-term drought, but their responses to long-term drought are unknown. Here we show that 14 years of summer drought changed calcareous grassland seed bank composition, reducing its size and richness, and that these responses do not simply reflect patterns in the above-ground vegetation. Moreover, the effect of drought was larger on seed banks than on vegetation, and above-ground responses mediated by soil depth were less evident in the seed bank than in the vegetation. These results demonstrate that the severity of drought effects on calcareous grasslands is larger than previously thought, and show that this ecosystem is highly vulnerable and has low resilience to predicted decreases in soil moisture

Polyploidy affects the seed, dormancy and seedling characteristics of a perennial grass, conferring an advantage in stressful climates

Polyploidy (the state of having more than two genome copies) is widely distributed in flowering plants and can vary within species, with polyploid races often associated with broad ecological tolerances. Polyploidy may influence within‐species variation in seed development, germination and establishment. We hypothesized that interactions between polyploidy and the seed developmental environment would affect subsequent dormancy, germination and early growth traits, particularly in stressful environments. Using seeds developed in a common garden under ambient and warmed conditions, we conducted germination trials under drought and temperature stress, and monitored the subsequent growth of seedlings. The study species, Themeda triandra, is a widespread, keystone, Australian native grass and a known polyploid complex. Tetraploid plants produced heavier, more viable seeds than diploids. Tetraploids were significantly more dormant than diploids, regardless of seed developmental environment. Non‐dormant tetraploids were more sensitive to germination stress compared to non‐dormant diploids. Finally, tetraploid seedlings were larger and grew faster than diploids, usually when maternal plants were exposed to developmental temperatures atypical to the source environment. Seed and seedling traits suggest tetraploids are generally better adapted to stressful environments than diploids. Because tetraploid seeds of T. triandra are more dormant they are less likely to germinate under stress, and when they do germinate, seedling growth is rapid and independent of seed developmental environment. These novel results demonstrate that polyploidy, sometimes in interaction with developmental environment and possibly also asexuality, can have within‐species variation in seed and seedling traits that increase fitness in stressful environments

Appendix C. Potential plant hosts for alfalfa mosaic virus present in New South Wales, Australia.

Potential plant hosts for alfalfa mosaic virus present in New South Wales, Australia

Component loadings of ten variables based on principal components analysis of site-level climatic and soil data.

1<p>Climatic data for the May to October growing season (1910–2010) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049000#s2" target="_blank">methods</a>). Potential evapotranspiration (PET); atmospheric water balance (AWB) = precipitation- PET.</p>2<p>Component loadings above 0.400 or below – 0.400 are in bold.</p

Appendix B. Geographic location of sites with alfalfa mosaic virus, white clover mosaic virus, and clover yellow vein virus in the study region.

Geographic location of sites with alfalfa mosaic virus, white clover mosaic virus, and clover yellow vein virus in the study region

Appendix A. Key vegetation communities and habitats surveyed in the study region.

Key vegetation communities and habitats surveyed in the study region