Many soils have intrinsically low concentrations of available phosphorus (P), which is a major limitation to crop and pasture growth. Regular applications of P have underpinned agricultural productivity internationally, and fertiliser use now constitutes one of the largest variable input costs to farming. Globally, high-quality reserves of P are being depleted and price increases are likely in the future. In addition, the effects of P pollution on water quality are attracting legislative regulation. Hence, there is a need to improve P-use efficiency (PUE) in farming systems.

Progress in improving PUE has been limited for several reasons, including: inconsistent definitions of PUE, inappropriate phenotyping, incomplete understanding of the controls of P uptake, lack of field validation, and little consideration of genotype × environment interactions that affect the expression of PUE. With greater consideration of these limitations, the powerful array of molecular and genomic tools currently available promises considerable advances in developing more P-efficient crops. Stronger interaction between molecular science and the traditional disciplines of plant breeding, crop physiology, soil science, and agronomy will allow new opportunities to study genetic differences in PUE, bringing P-efficient crops closer to reality.

This article reviews current knowledge for Australia over the occurrence, losses caused, epidemiology, and management of virus diseases of perennial pasture legumes. Currently, 24 viruses have been found infecting perennial pasture legumes, and one or more viruses have been detected in 21 of these species. These viruses are transmitted by insect vectors, non-persistently or persistently, by contact or via seed. Their modes of transmission are critical factors determining their incidences within pastures in different climatic zones. Large-scale national or state surveys of lucerne (alfalfa) (Medicago sativa) and white clover (Trifolium repens) pastures revealed that some viruses reach high incidences. Infection with Alfalfa mosaic virus (AMV) was very widespread in lucerne stands, and with AMV and White clover mosaic virus (WClMV) in white clover pastures. Several other viruses are potentially important in pastures in these and other perennial temperate/Mediterranean pasture species. Data demonstrating herbage yield losses, diminished pasture persistence, and impaired nitrogen fixation/nodule function are available for AMV in lucerne, and AMV, WClMV, and Clover yellow vein virus in white clover. Integrated Disease Management approaches involving phytosanitary, cultural, chemical, and host resistance control measures are available to minimise virus infection in lucerne and white clover. Research on virus diseases of perennial tropical–subtropical pasture legumes has focussed almost entirely on virus identification, and information on their incidences in pastures, the losses they cause, and how to control them is lacking. Overall, viruses of perennial pasture legumes are least studied in South Australia and the Northern Territory. These and other critical research and development gaps that need addressing are identified.

This paper reviews current knowledge for Australia over the occurrence, losses caused, epidemiology, and management of virus diseases of pasture grasses. It also reviews all records of viruses in wild grasses likely to act as alternative host reservoirs for virus spread to nearby pastures or crops. Currently, 21 viruses have been found infecting 36 pasture or forage grass species and 59 wild grass species. These viruses are transmitted by arthropod vectors (mites or insects) or, in one instance, via grass seeds. Their modes of transmission are critical factors determining their incidences within pastures in different climatic zones. Large-scale surveys of perennial grass pastures growing in regions with temperate–Mediterranean climates revealed that Barley yellow dwarf virus (BYDV), Cereal yellow dwarf virus (CYDV), and Ryegrass mosaic virus (RyMV) sometimes reach high infection incidences. The same was true for BYDV and CYDV when perennial pasture grasses and wild grasses growing outside pastures were surveyed to establish their occurrence. Smaller scale surveys of grasses growing both inside and outside annual pastures found that Wheat streak mosaic virus (WSMV) infection could also reach high incidences in some annual grass species. Herbage yield loss data are available demonstrating potentially serious impacts on pasture production under Australian conditions from BYDV infection in perennial ryegrass swards, and from RyMV infection in both perennial and Italian ryegrass swards. Also, infection with BYDV or RyMV diminished the ability of infected pasture grass plants to compete with pasture legumes or weeds. Host resistance to BYDV, CYDV, and/or RyMV has been identified within a few temperate–Mediterranean pasture grasses, and is available for use in Australian pasture breeding programs. Integrated Disease Management tactics involving phytosanitary, cultural, chemical, and host resistance measures were devised against BYDV, CYDV, and RyMV infection in mixed species pasture, but no field experiments were undertaken with pasture grasses to validate their inclusion. Several other grass viruses that occur in other countries, but have not been looked for in Australia, are potentially important, especially in temperate–Mediterranean pasture grass species. With few exceptions, research on viruses of perennial or annual tropical–subtropical pasture or wild grass species growing within or outside pastures has focussed only on virus identification and characterisation studies, and information on incidences in pastures, losses caused, epidemiology, and management is lacking. Critical research and development gaps that need addressing are identified.

Here we propose that the perspective of phenotypic plasticity can enhance our understanding of the role of fertile tillers in accommodating environmental variation. We tested the hypothesis that the plasticity of yield correlates with the plasticity of ear number using free-tillering (–tin) and reduced-tillering ( tin) sister wheat lines in two genetic backgrounds, Lang and Silverstar. Crops were grown in 10 rainfed environments resulting from the combination of seasons, sites, nitrogen rates, and sowing dates. The combination of lines and environments generated a range from 157 to 357 ears m^–2 at harvest, and a yield range from 1.9 to 4.2 t ha^–1. Plasticity was quantified with two methods, slopes of reaction norms and variance ratios; both methods returned the same ranking of lines for both ear number and yield.

The tin allele reduced the plasticity of both ear number and yield in Lang but not in Silverstar. The reduced plasticity associated with the tin allele in Lang had two components: a small reduction in ear number under low-yielding conditions, and a large reduction in the capacity to respond to higher yielding environments. Consistent with our working hypothesis, plasticity of yield and plasticity of ear number were correlated (R² = 0.81, P = 0.01). Plasticity of ear number was associated with the plasticity of shoot biomass at harvest (R² = 0.74, P = 0.006), and plasticity of biomass was associated with the plasticity of yield (R² = 0.86, P = 0.0009). This suggests that the environmental responsiveness of yield was partially mediated by the environmental responsiveness of fertile tillers.

We found positive correlations between plasticity of ear number and plasticity of several traits including biomass, radiation-use efficiency and water-use efficiency, and a negative correlation between plasticity of ear number and plasticity of seeds per ear. Ear number per se was unrelated to biomass, radiation-use efficiency, water-use efficiency, and seeds per ear. We conclude that a dual focus on traits per se and their plasticity is a fruitful approach to understand the phenotype, particularly when genotype × environment interaction is large.

Due to the complex genetic architecture of perennial ryegrass, based on an obligate outbreeding reproductive habit, association-mapping approaches to genetic dissection offer the potential for effective identification of genetic marker–trait linkages. Associations with genes for agronomic characters, such as components of herbage nutritive quality, may then be utilised for accelerated cultivar improvement using advanced molecular breeding practices. The objective of the present study was to evaluate the presence of such associations for a broad range of candidate genes involved in pathways of cell wall biosynthesis and carbohydrate metabolism. An association-mapping panel composed from a broad range of non-domesticated and varietal sources was assembled and assessed for genome-wide sequence polymorphism. Removal of significant population structure obtained a diverse meta-population (220 genotypes) suitable for association studies. The meta-population was established with replication as a spaced-plant field trial. All plants were genotyped with a cohort of candidate gene-derived single nucleotide polymorphism (SNP) markers. Herbage samples were harvested at both vegetative and reproductive stages and were measured for a range of herbage quality traits using near infrared reflectance spectroscopy. Significant associations were identified for ∼50% of the genes, accounting for small but significant components of phenotypic variance. The identities of genes with associated SNPs were largely consistent with detailed knowledge of ryegrass biology, and they are interpreted in terms of known biochemical and physiological processes. Magnitudes of effect of observed marker–trait gene association were small, indicating that future activities should focus on genome-wide association studies in order to identify the majority of causal mutations for complex traits such as forage quality.

The response patterns during water deficit stress and subsequent recovery of two forage species, Medicago truncatula and Sulla carnosa, were studied. After germination and pre-treatment, seedlings were individually cultivated for two months under two irrigation modes: 100% and 33% of field capacity. Measured parameters were plant growth, water relations, leaf osmotic potential, lipid peroxidation, and leaf inorganic (Na and K ) and organic (proline and soluble sugars) solute contents, as well as delta-1-pyrroline-5-carboxylate synthase (P5CS) and proline dehydrogenase (PDH) activities. Our results showed that under control conditions, and in contrast to roots, no significant differences were observed in shoot biomass production between the two species. However, when subjected to water-deficit stress, M. truncatula appeared to be more tolerant than S. carnosa (reduction by 50 and 70%, respectively). In the two studied species, water-deficit stress led to an increase in root/shoot ratio and leaf proline and soluble sugar contents, and a decrease in leaf osmotic potential. Enzymatic assay revealed that in the two species, P5CS activity was stimulated whereas that of PDH was inhibited under stress conditions. Despite greater accumulation of proline, sugar, and potassium in leaves of S. carnosa, M. truncatula was more tolerant to water deficit. This was essentially due to its capacity to control tissue hydration and water-use efficiency, in addition to its greater ability to protect membrane integrity. Following stress relief, M. truncatula and S. carnosa showed partial re-establishment of growth capacity.

A significant challenge for the pastoral farming systems is to maintain or increase production while reducing leaching of nitrogen, and for pastoral systems, this means reducing leaching from urine patches. Here we explore the potential impact of four ryegrass characteristics to increase pasture production and reduce leaching from ryegrass–white clover pastures. We focus on understanding which characteristics are desirable, the stage before investigating the achievability of those characteristics in a breeding program. Those characteristics were: the winter- or summer-dominance of growth (GP); the ability of the plant to intercept radiation at low pasture mass (LI); rooting depth (RD); and resistance to moderate water stress (WF). The impact of these ryegrass characteristics, both singly and combined within a ryegrass–clover pasture, was explored across a range of soils, climates, irrigation management, and urine patch concentrations using the process-based model APSIM.

Of the four characteristics tested, LI was the most effective in increasing production and reducing leaching in all environments. The characteristics RD and WF were moderately effective, with RD having a greater impact on reducing leaching whereas WF had a greater effect on increasing production. The characteristic with the least impact was GP and it seems that ryegrass is currently well adapted for typical temperatures in New Zealand. The production and environmental effects of the characteristics were additive. The characteristics should be investigated further in the typically more diverse mixtures normally found in pastures but show promise for achieving improved production while reducing leaching provided they can be achieved in a breeding program.

Salt-affected land varies spatially and seasonally in terms of soil salinity and depth to the watertable. This paper asks whether native and naturalised species growing on saltland can be used as ‘indicators’ of saltland capability. The percentage cover of native and naturalised species was recorded in spring 2004 and 2005 across saltland transects on three sites in Western Australia. The presence of these plants was related to average soil salinity (EC_e) at depth (25–50 cm), and depth to the watertable in spring. Eight naturalised species occurred with ≥40% cover on the sites. Species preferences varied, with some such as samphire (Tecticornia pergranulata) and puccinellia (Puccinellia ciliata) only occurring with shallow watertables (<0.7 m deep) and with EC_e values >16 dS/m. Other species such as capeweed (Arctotheca calendula) and annual ryegrass (Lolium rigidum) were dominant where watertables were deeper (>1.3 m) and salinity levels lower (ECe values 2–8 and 4–16 dS/m, respectively). Our data suggest that some of the species recorded can be used as indicators of saltland capability and, further, can predict the most productive species to sow in that area. Other species were found not to be good indicators as they displayed more opportunistic habitat requirements.