Kioumars Ghamkhar

Temperate pasture legumes in Australia—their history, current use, and future prospects

Abstract. Australian farmers and scientists have embraced the use of new pasture legume species more than those in any other country, with 36 annual and 11 perennial legumes having cultivars registered for use. Lucerne (Medicago sativa), white clover (Trifolium repens), and red clover (T. pratense) were introduced by the early European settlers and are still important species in Australia, but several other species, notably annual legumes, have been developed specifically for Australian environments, leading to the evolution of unique farming systems. Subterranean clover (T. subterraneum) and annual medics (Medicago spp.) have been the most successful species, while a suite of new annual legumes, including serradellas (Ornithopus compressus and O. sativus), biserrula (Biserrula pelecinus) and other Trifolium and Medicago species, has expanded the range of legume options. Strawberry clover (T. fragiferum) was the first non-traditional, perennial legume commercialised in Australia. Other new perennial legumes have recently been developed to overcome the soil acidity and waterlogging productivity constraints of lucerne and white clover and to reduce groundwater recharge and the spread of dryland salinity. These include birdsfoot trefoil (Lotus corniculatus), Talish clover (T. tumens), and hairy canary clover (Dorycnium hirsutum). Stoloniferous red clover cultivars and sulla (Hedysarum coronarium) cultivars adapted to southern Australia have also been released, along with a new cultivar of Caucasian clover (T. ambiguum) aimed at overcoming seed production issues of cultivars released in the 1970s. New species under development include the annual legume messina (Melilotus siculus) and the perennial legume narrowleaf lotus (L. tenuis) for saline, waterlogged soils, and the drought-tolerant perennial legume tedera (Bituminaria bituminosa var. albomarginata). Traits required in future pasture legumes include greater resilience to declining rainfall and more variable seasons, higher tolerance of soil acidity, higher phosphorous utilisation efficiency, lower potential to produce methane emissions in grazing ruminants, better integration into weed management strategies on mixed farms, and resistance to new pest and disease threats. Future opportunities include supplying new fodder markets and potential pharmaceutical and health uses for humans and livestock. New species could be considered in the future to overcome constraints of existing species, but their commercial success will depend upon perceived need, size of the seed market, ease of establishment, and management and safety of grazing animals and the environment. Molecular biology has a range of potential applications in pasture legume breeding, including marker-assisted and genomics-assisted selection and the identification of quantitative trait loci and candidate genes for important traits. Genetically modified pasture plants are unlikely to be commercialised until public concerns are allayed. Private seed companies are likely to play an increasingly important role in pasture legume development, particularly of mainstream species, but the higher risk and more innovative breakthroughs are likely to come from the public sector, provided the skills base for plant breeding and associated disciplines is maintained.

Genetic improvement of subterranean clover (Trifolium subterraneum L.). 1. Germplasm, traits and future prospects

Abstract. Subterranean clover (Trifolium subterraneum L.) is the most widely sown annual pasture legume species in southern Australia, valued in the livestock and grains industries as a source of high-quality forage and for its ability to fix atmospheric nitrogen. From its initial accidental introduction into Australia in the 19th Century and subsequent commercialisation in the early 1900s, 45 cultivars have been registered in Australia. These consist of 32 cultivars of ssp. subterraneum, eight of ssp. yanninicum, and five of ssp. brachycalycinum and range in flowering time from 77 to 163 days from sowing, enabling the species to be grown in a diversity of rainfall environments, soil types, and farming systems. Eleven of these cultivars are introductions from the Mediterranean region, 15 are naturalised strains collected in Australia, 18 are the products of crossbreeding, and one is derived from mutagenesis. Cultivars developed in Italy have been commercialised for the local market, whereas other cultivars developed in Spain, Portugal, and France have not had commercial seed production. Important traits exploited include: (i) selection for low levels of the oestrogenic isoflavone formononetin, which causes reduced ewe fertility; (ii) increased levels of dormancy imposed by seed-coat impermeability (hard seeds) for cultivars aimed at crop rotations or unreliable rainfall environments; (iii) strong burr-burial ability to maximise seed production; (iv) resistance to important disease pathogens for cultivars aimed at medium- and high-rainfall environments, particularly to Kabatiella caulivora and root rot pathogens; (v) resistance to pests, particularly redlegged earth mites; and (vi) selection for unique leaf markings and other morphological traits (where possible) to aid cultivar identification. Cultivar development has been aided by a large genetic resource of ∼10 000 accessions, assembled from its centre of origin in the Mediterranean Basin, West Asia, and the Atlantic coast of Western Europe, in addition to naturalised strains collected in Australia. The development of a core collection of 97 accessions, representing almost 80% of the genetic diversity of the species, and a genetic map, provides a platform for development of future cultivars with new traits to benefit the livestock and grains industries. New traits being examined include increased phosphorous-use efficiency and reduced methane emissions from grazing ruminant livestock. Economic analyses indicate that future trait development should focus on traits contributing to increased persistence and autumn–winter productivity, while other potential traits include increased nutritive value (particularly of senesced material), increased N2 fixation ability, and tolerance to cheap herbicides. Beneficial compounds for animal and human health may also be present within the species for exploitation.

Strategies for developing a core collection of bladder clover (Trifolium spumosum L.) using ecological and agro-morphological data

Core collections are a way to improve the functioning of germplasm collections through systematic evaluation, exploitation, and improved management of the whole collection. The published sizes of cores have ranged from 10 to 30% of the collection. The first step in developing a core collection is usually stratification of the whole collection. We adopted three approaches in the process of core designation. First, the existing ecological data and newly acquired agro-morphological (evaluation) data were analysed to determine the optimal method for capturing the ecological and morphological diversity of accessions. Second, different selection strategies were compared to identify the most powerful analysis with the greatest likelihood of covering maximum diversity. Third, the correlation between the two datasets was investigated. The annual pasture legume, bladder clover (Trifolium spumosum L.), was used for this pilot study because 80% of the existing 398 accessions have near-complete ecological data. The study found that a two-step selection process using ecological data and stratified proportional strategy followed by combined datasets and maximising strategy best represents the whole collection of T. spumosum in the core.

Ecogeographical studies identify diversity and potential gaps in the largest germplasm collection of bladder clover (Trifolium spumosum L.)

Plant germplasm collections are important reservoirs of diversity for plant breeders and adding to the knowledge of the diversity among and within germplasm accessions helps plant breeders to use them more efficiently. The annual legume, bladder clover (Trifolium spumosum L.), was the model plant in this study. The hypothesis that ecogeographical variables are important sources of diversity in the germplasm collection of bladder clover and some variables are more important than others has been studied. Three themes have been addressed here: firstly, analysis of the existing passport data to determine a minimum set of ecogeographical descriptors required for capturing ecological aspects of each collection site; secondly, illustration of the ecogeographical regions and subregions using GIS techniques to identify areas with the greatest likelihood of filling gaps in the collection; thirdly, development of an approach for the evaluation of genetic diversity by grouping accessions with a focus on outliers within the collection using principal component and cluster analyses. In this paper the importance of longitude as a geographical factor has been documented and the overall ecogeographical diversity in the germplasm collection of bladder clover has been screened.

Biserrula pelecinus L. – genetic diversity in a promising pasture legume for the future

Abstract. Biserrula pelecinus L. is a Mediterranean annual pasture legume and performs best on well drained sandy loams and medium loams with a pH 4.5–7. It is not suited to areas prone to waterlogging but persists well, even with hard summer grazing and in rotational systems. It is deep-rooted and remains green long after traditional pastures have dried off. Diversity analysis of germplasm collection of 279 accessions using 18 agro-morphological traits, 22 eco-geographical specifications of the collection sites, and amplified fragment length polymorphisms markers was conducted to develop a core collection of ∼10% of the original collection. This core collection of 30 accessions from seven countries well represented the diversity of the whole collection. This core will be exploited for variation in photosensitivity effect in sheep together with other economically important traits challenging the livestock industry.

Variability of in vitro ruminal fermentation and methanogenic potential in the pasture legume biserrula (Biserrula pelecinus L.)

Abstract. Biserrula (Biserrula pelecinus L.) is an important annual pasture legume for the wheatbelt of southern Australia and has been found to have lower levels of methane output than other pasture legumes when fermented by rumen microbes. Thirty accessions of the biserrula core germplasm collection were grown in the glasshouse to examine intra-specific variability in in vitro rumen fermentation, including methane output. One biserrula cultivar (Casbah) was also grown at two field locations to confirm that low methanogenic potential was present in field-grown samples. All of the biserrula accessions had significantly reduced methane [range 0.5–8.4 mL/g dry matter (DM)] output compared with subterranean clover (28.4 mL/g DM) and red clover (36.1 mL/g DM). There was also significant variation in fermentability profiles (except for volatile fatty acids) among accessions of the core collection. Methanogenic potential exhibited 86% broad-sense heritability within the biserrula core collection. The anti-methanogenic and gas-suppressing effect of biserrula was also confirmed in samples grown in the field. In conclusion, biserrula showed variability in in vitro fermentation traits including reduced methane production compared with controls. This bioactivity of biserrula also persists in the field, indicating scope for further selection of biserrula as an elite methane-mitigating pasture.

In vitro ruminal fermentation characteristics and methane production differ in selected key pasture species in Australia

Abstract. Thirteen current and potential pasture species in southern Australia were examined for differences in their nutritive values and in vitro rumen fermentation profiles, including methane production by rumen microbes, to assist in selection of pasture species for mitigation of methane emission from ruminant livestock. Plants were grown in a glasshouse and harvested at 7 and 11 weeks after sowing for in vitro batch fermentation, with nutritive values assessed at 11 weeks of growth. The pasture species tested differed significantly (P < 0.001) in methane production during in vitro rumen fermentation, with the lowest methane-producing species, Biserrula pelecinus L., producing 90% less methane (4 mL CH4 g–1 dry matter incubated) than the highest methane-producing species, Trifolium spumosum L. (51 mL CH4 g–1 dry matter incubated). Proxy nutritive values of species were found not to be useful predictors of plant fermentation characteristics or methane production. In conclusion, there were significant differences in fermentative traits, including methane production, among selected pasture species in Australia, indicating that the choice of fodder species may offer a way to reduce the impact on the environment from enteric fermentation.

Hotspots and gaps in the world collection of subterranean clover (Trifolium subterraneum L.)

Subterranean clover (Trifolium subterraneum L.) is the most important annual pasture legume in the winter-dominant rainfall areas of Southern Australia. Systematic germplasm collections of subterranean clover from its centre of origin have been made since the 1950s, particularly by Australian scientists, in order to broaden the genetic base of the species. The present study reports on a meta-analysis of the distribution of the world collection of subterranean clovers and their relationships to eco-geographic variables of the collection sites in their native habitat. Diversity hotspots (areas rich in number of accessions and containing a high diversity of sub-species) and also gaps (areas with particular traits un- or under-represented in collections) were identified. This was achieved using a stratified data system to evaluate eco-geographical and agro-morphological data which incorporated three tiers of information for the subterranean clover collection: (1) information from each collection site, including ecological data; (2) information on the phenotypic diversity within each collection site; and (3) plant agro-morphological data from each sample grown under controlled conditions. Correlations were found between some eco-geographic conditions and agronomic performance. These included correlations between latitude and flowering time, mean temperature in winter and winter productivity and precipitation in summer and seed dormancy. The present study concluded that subterranean clover versatility is greater than suggested in the past. The results of the current analysis provide a guide for future collecting missions to specific regions towards areas of maximum diversity (hotspots) and unknown diversity (gaps).