A major challenge faced by today’s white clover breeder is how to manage resources within a breeding program. It is essential to utilise these resources with sufficient flexibility to build on past progress from conventional breeding strategies, but also take advantage of emerging opportunities from molecular breeding tools such as molecular markers and transformation. It is timely to review white clover breeding strategies. This background can then be used as a foundation for considering how to continue conventional plant improvement activities and complement them with molecular breeding opportunities. In this review, conventional white clover breeding strategies relevant to the Australian dryland target population environments are considered. Attention is given to: (i) availability of genetic variation, (ii) characterisation of germplasm collections, (iii) quantitative models for estimation of heritability, (iv) the role of multi-environment trials to accommodate genotype-by-environment interactions, (v) interdisciplinary research to understand adaptation to dryland environments, (vi) breeding and selection strategies, and (vii) cultivar structure. Current achievements in biotechnology with specific reference to white clover breeding in Australia are considered, and computer modelling of breeding programs is discussed as a useful integrative tool for the joint evaluation of conventional and molecular breeding strategies and optimisation of resource use in breeding programs. Four areas are identified as future research priorities: (i) capturing the potential genetic diversity among introduced accessions and ecotypes that are adapted to key constraints such as summer moisture stress and the use of molecular markers to assess the genetic diversity, (ii) understanding the underlying physiological/morphological root and shoot mechanisms involved in water use efficiency of white clover, with the objective of identifying appropriate selection criteria, (iii) estimation of quantitative genetic parameters of important morphological/physiological attributes to enable prediction of response to selection in target environments, and (iv) modelling white clover breeding strategies to evaluate the opportunities for integration of molecular breeding strategies with conventional breeding programs.

The importance of white clover as a pasture legume of international significance has led to major investment in research on ecophysiology, germplasm conservation, and white clover improvement. Despite the agronomic merit and economic significance of white clover, Australia lacks white clover cultivars that possess adaptive characteristics for persistence in mixed swards under sheep and cattle grazing. The major problem with contemporary white clover cultivars is that clover biomass fluctuates widely from year to year. This lack of reliability, particularly in dryland environments, is largely due to poor survival during summer moisture stress that is common to much of the Australian white clover zone. Factors such as edaphic constraints, intolerance of grass competition and close grazing, and lack of winter growth in cold environments also influence the contribution of white clover to pasture performance. This paper considers the mechanisms of regeneration, adaptive characteristics, and significance of white clover for animal production, and reflects on breeding objectives for white clover improvement.

Improving the genetic merit of temperate forage legumes helps ensure profitability and sustainability of our Australasian pastoral industries. Today’s plant breeders are supported by a range of underpinning research activities including genetic resources exploration and enhancement, plant physiology, plant health, feed quality, agronomy, quantitative genetics and plant biotechnology; and have collaborative interfaces with animal and farm systems science. Lifting the rate of gain by integration of molecular tools, innovative breeding strategies, and new genetic resources is the major objective of our white clover breeding network. This paper, presented at the Australasian Grassland Association’s recent Legume Symposium, focuses on the key research and development achievements in white clover breeding for Australasia, and on the success and future of an Australasian collaboration to breed improved cultivars for the region’s temperate environments. The paper reports on successful developments in the areas of improving white clover root systems for phosphate uptake, pest tolerance, development of novel inter-specific hybrids and marker-aided breeding. The successful trans-Tasman collaboration in white clover breeding and future work is also discussed.

Summary. White clover was introduced to Australia with the early European settlers in the late 18th century and is now the most valuable pasture legume in high rainfall temperate regions of Australia. Through a process of ingress and naturalising in conjunction with pastoral expansion during the 19th century and widespread pasture improvement in the 20th century, white clover now occupies 6 million hectares in Australia and is of major significance for the sheep, beef cattle and dairy industries. This paper describes these historical influences on formation of the white clover zone in Australia and the continuing requirement for better adapted cultivars in key agro-geographic regions, with particular close reference to the northern tablelands of New South Wales—the most extensive dryland region. These considerations provide a basis for defining breeding objectives for white clover improvement in Australia.

A series of experiments was undertaken to determine population statistics for in vitro organic matter digestibility (in vitro OMD) data and to examine the effects of basal diet, donor animal and precollection fasting interval on the activity and specificity of rumen fluid inoculum. The experiments utilized wether sheep, a diverse set of pasture grass and legume feeds prominent in the Australian subtropics and the Tilley and Terry in vitro digestibility procedure running under the operating pressure of a practising feeds evaluation laboratory.The standard errors of in vitro OMD estimates for within and between batch runs were ±0-88 X 10"^ and 0-62 x 10"^, respectively. These error terms were used to develop protocols to accept, reject or scale raw in vitro OMD data. Differences between donor animals in the activity of rumen fluid were highly significant. Extending the precollection fasting interval beyond 16 h was associated with a substantial decline in inoculum activity.An in vitro-in vivo calibration relationship based on fifteen test feeds and using lucerne (Medicago sativa) as basal diet was described by the linear model y=l-3 x-0-195±4-9x 10"r =0-79 (y = in vivo OMD, x = />i vitro OMD). Despite large effects of basal diet on both the absolute values and relative ranking of test feeds, neither the RSD nor r values were improved using alternative diets to lucerne chaff.The results highlight the need to formally standardize the analytical and biological components of the in vitro digestibility procedure to safeguard the integrity of data.

A genetic experiment was conducted using 80 full-sib families in irrigated and dryland treatments under the summer moisture stress conditions of the Northern Tablelands of New South Wales, over 3 years. This paper reports on the effects of climatic and soil moisture conditions, the genetic variation for stolon attributes and seasonal herbage yield, and the development of new recombinant genotypes in relation to the association between stolon attributes and herbage yield. Large components of variance were estimated for genotype-by-environment-by-year interactions for the attributes stolon density, number of branches, number of nodes, number of rooted nodes, stolon thickness, root diameter, internode length, and summer herbage yield. The combined analysis of variance across environments and years indicated the presence of genetic variation for the stolon attributes stolon density, number of branches, number of nodes, stolon thickness, internode length, and herbage yield. Crossing of the morphologically contrasting cultivars El Lucero × Tahora × Duron, and Barbian × El Lucero, resulted in generating genotypic recombinants with new associations between herbage yield and stolon density, number of branches, number of nodes, and number of rooted nodes. Evaluation of the full-sib families and check cultivars (cvv. Haifa and Huia) identified 5 full-sib families with relatively higher herbage yield, stolon density, number of branches, number of nodes, and number of rooted nodes than cultivars Haifa and Huia.

A breeding project has developed a new synthetic white clover (Trifolium repens L.) cultivar, Grasslands Trophy, that possesses tolerance of summer moisture stress in dryland pasture environments in the 850–1250 mm average annual rainfall temperate perennial pasture zone in eastern Australia. The breeding strategy used to develop Grasslands Trophy was an in situ breeding cycle for: (i) identifying and selecting superior genotypes, (ii) crossing elite germplasm and (iii) progeny testing derived breeding lines for the expression of key agronomic and grazing value traits. The primary selection criteria were early vigour, herbage yield, persistence and seed yield potential. Parental selection was also applied for seed yield, uniformity of leaf size, uniform flowering pattern and freedom from disease and virus symptoms. Grasslands Trophy is medium–large in leaf size with stable leaf size, combines intermediate stolon density with intermediate stolon thickness, and expresses high stolon survival and strong autumn regrowth following summer moisture stress. Grasslands Trophy has mid-season flowering maturity, intensive flowering prolificacy and high seed yield capability. Agronomic results from trials in northern New South Wales and New Zealand indicate that Grasslands Trophy has broad adaptation, expresses high summer and winter growth activity, and is reliably persistent for at least 4 years.

Birdsfoot trefoil (Lotus corniculatus L.) is a potentially important alternative legume for recharge landscapes in the high rainfall zone in eastern Australia. However, in the summer rainfall region in northern New South Wales (NSW) where birdsfoot trefoil has the greatest potential application, flowering and seed set are limited by short daylength. Consequently, existing birdsfoot trefoil cultivars do not set enough seed to develop a seedbank that sustains a productive persistent stand. A breeding program was undertaken to develop birdsfoot trefoil cultivars adapted to short photoperiod to increase the area sown to deep-rooted perennials in the grazing lands in eastern Australia. Three new birdsfoot trefoil experimental varieties, Phoenix, Venture and Matador, were developed through: (1) phenotypic selection within cv. Grasslands Goldie for flowering intensity and pod set, (2) phenotypic selection for these same traits in a broader sample of 49 world-sourced lines, and (3) selection for prostrate growth habit among progeny of pair-crosses between erect and prostrate accessions identified as productive in southern NSW. Following two cycles of selection for flowering prolificacy and pod set, the average number of umbels per stem in the Goldie-derived populations was five times greater than in the commercial Goldie population; this response to selection closely approximated the predicted response based on previous estimates of heritability and phenotypic variance for this trait. In comparison with Goldie, the Syn1 and Syn2 populations of the three experimental varieties consistently expressed earlier flowering maturity and higher seed yield potential in glasshouse and field trials in northern NSW. While germination rate and seedling vigour of the three experimental varieties was slightly less than Goldie, intensive selection pressure on reproductive traits did not compromise seasonal herbage production.