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Germplasm of the perennial pasture grass Phalaris aquatica L., from Sardinia, Italy, is a potentially valuable source for grass breeders owing to climatic similarities to regions where P. aquatica is used, a relatively high incidence of acidic soils, and exposure to prolonged grazing pressure. At field sites in south-eastern Australia, Sardinian accessions were compared as spaced plants and drill-rows with accessions from southern Europe and north-western Africa and with commercial cultivars. They were also evaluated in grazed swards at three sites over 4 years under conditions that challenge persistence, including heavy grazing pressure, acid soils and drought. Morphologically, the accessions were comparatively dense, fine and short, with similarities to southern European accessions and cultivars of the cv. Australian type. However, they were earlier heading and more summer-dormant, particularly those from southern Sardinia. In drill-rows, Sardinian accessions were later heading and less productive in winter than accessions from Morocco. In swards, Sardinian accessions had lower seedling vigour and winter growth potential than modern winter-active cultivars. However, they were dense and persistent under high grazing pressure, and some accessions survived better than all cultivars on an acid, low-fertility soil. Developing cultivars that are superior to the cv. Australian type with acceptable seed production and alkaloid levels presents a challenge to breeders. However Sardinian germplasm offers a range of maturity times combined with higher levels of summer dormancy and a grazing-tolerant morphology, attributes that may expand the area of adaptation of the species into the hotter and more drought-prone margin. Germplasm of Phalaris aquatica from Sardinia is a potentially valuable source of grass cultivars for livestock production in regions that experience dry summers. Accessions from Sardinia displayed lower seedling vigour and winter growth than modern cultivars but were denser and more persistent under high grazing pressure and had good spring production, and some accessions survived better on difficult soils. The germplasm displayed attributes that could help livestock industries facing multiple stresses in the future. [ABSTRACT FROM AUTHOR]

Background: The ability to finish livestock on pasture over the summer–autumn period could improve the profitability of red meat enterprises in drought‐prone temperate regions. In south‐eastern Australia, traditional perennial options are limited by poor warm‐season performance (phalaris, Phalaris aquatica L.) and widespread environmental constraints (lucerne, Medicago sativa L.). We aimed to identify perennial species suitable for summer–autumn finishing. Methods: We tested pure swards of summer‐active perennial grasses and herbs (20 cultivars across 14 species) in replicated small‐plot experiments at two sites on the Southern Tablelands of New South Wales, Australia. We assessed early persistence, productivity and warm‐season nutritive characteristics over 2–3 years. Results: Lucerne and chicory (Cichorium intybus L.) persisted well through drought and produced herbage of high quantity and quality through summer–autumn. Digit grass (Digitaria eriantha Steud.) was highly persistent and productive but nutritive values were generally poor. Cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and plantain (Plantago lanceolata L.) were productive but less persistent through drought, while nutritive values were sometimes inadequate. Conclusions: Chicory is a good alternative to lucerne, given its excellent summer–autumn performance, ability to survive droughts and superior acid soil tolerance. If appropriate management resolves issues with persistence and nutritive value, several of the other species could also be used to close the warm‐season feed gap in drought‐prone temperate environments. [ABSTRACT FROM AUTHOR]

Context: High-quality, summer-active pastures could improve meat production in south-eastern Australia by facilitating livestock finishing over summer, with legumes critical for enhancing the nutritive value of pasture mixes. Available legumes vary in their ability to withstand moisture stress and grazing. Aims: We aimed to identify legumes suitable for a summer–autumn finishing system. Methods: We tested pure swards of 12 cultivars across eight legume species in replicated small-plot experiments at Goulburn and Bombala, New South Wales, assessing productivity, persistence and warm-season nutritive characteristics over 2–3 years. Key results: Lucerne (Medicago sativa) was clearly the most productive species during summer and outperformed the clovers (Trifolium spp.) in terms of persistence and productivity throughout most of the experimental period at both sites, except during autumn 2021 after high rainfall in March. Caucasian clover (T. ambiguum) was also highly persistent at both sites. Talish clover (T. tumens) and strawberry clover (T. fragiferum) were more persistent than white clover (T. repens) and red clover (T. pratense). White clover recovered strongly under high rainfall after drought, whereas red clover established rapidly but showed less capacity for post-drought recovery. Hybrid Caucasian × white clover was the least productive legume. Alternative clover species sometimes had slightly lower values of nutritive characteristics than white clover; red clover sometimes had distinctly lower values. Conclusions: Lucerne performed best but several clovers were also productive, persistent and of high nutritive value over the summer–autumn period. Implications: Talish, Caucasian and strawberry clovers warrant further investigation for inclusion in summer-active pastures in south-eastern Australia. Profitability of livestock production over summer–autumn in the temperate environment of south-eastern Australia could be improved by including legumes in pastures that are persistent, productive and of high nutritive value. Evaluation of a range of legume species and cultivars showed that lucerne remained the most reliably productive warm-season option where soil conditions support it. Talish, Caucasian and strawberry clovers were persistent and of high nutritive value, warranting further evaluation in special-purpose warm-season pastures. [ABSTRACT FROM AUTHOR]

The adaptation of introduced perennial grasses in southern Australia expanded with the discovery of the Mediterranean grass phalaris (Phalaris aquatica L.) as a valuable pasture species, and the introduction of Mediterranean ecotypes of orchardgrass (Dactylis glomerata L.), and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] displaying summer dormancy. In contrast, native grasses of agricultural importance appear to have little or no endogenous summer dormancy. A brief history of cultivar development from Mediterranean germplasm is presented. Recent developments include cultivars based on summer-dormant subsp. hispanica orchardgrass and the release of Mediterranean-type cultivars of tall fescue. Phalaris depends on a deep root system and summer dormancy for its summer survival. Cultivars based on more summer-dormant Moroccan ecotypes have been developed for drier environments. Work to improve phalaris for hotter, summer-dominant rainfall areas is being extended to enhance the range of perennials for the cropping zone. In addition to ecotype evaluation, breeders should employ recurrent selection in cultivars and populations such as those developed recently for low- to medium-rainfall areas in orchardgrass and tall fescue. [ABSTRACT FROM AUTHOR]

Context: Improving the stability of legumes in grasslands in the face of variable seasonal conditions is key to mitigating risks posed by drought. Aims: We assessed the persistence of a range of legume species and cultivars in order to inform legume choice for pasture improvement and identify priority species for further development. Methods: Twenty field experiments in four series were conducted at sites with contrasting seasonal and soil characteristics in the 'high-rainfall' (560–920 mm long-term average) Tablelands and Monaro regions of New South Wales, Australia. Legumes were grown as pure swards and assessed periodically for seedling density, plant frequency and dry matter for up to 5 years. Key results: Legume dry matter production was positively correlated with plant frequency. However, most legumes persisted poorly at most sites, particularly on soils of lower fertility. Subterranean clover (Trifolium subterraneum) cv. Goulburn was the best performing cultivar of that species across sites on the Southern Tablelands and Monaro. Yellow serradella (Ornithopus compressus) cvv. Avila and Yellotas showed promising persistence, particularly under drought conditions. White clover (T. repens) was the most broadly adapted of the perennial legumes across a range of soils, but persistence was still inadequate at many sites. Lucerne (Medicago sativa) was approximately twice as productive as the next-most productive species when soil conditions suited its growth, but it failed to persist on acidic, low-fertility soils. Conclusions: Serradella species (yellow and French, O. sativus) and white clover, in conjunction with subterranean clover, offer the best near-term prospects for diversifying legume productivity and resilience under variable seasonal conditions in tableland environments. Implications: An increased focus on phenology and seed characteristics is suggested to improve the persistence of annual and facultative perennial legume species in grasslands. Serradella and white clover are identified as the highest priorities for cultivar development for tableland environments of south-eastern Australia. This study evaluated the stability and persistence of a range of legume species and cultivars to identify viable options for grasslands of south-eastern Australia. Yellow and French serradella, white clover and subterranean clover were identified as priority species because they are already, or are close to being, viable options for use in grasslands. An increased focus on phenology and seed characteristics is suggested to improve the persistence of white clover and serradella in grasslands. [ABSTRACT FROM AUTHOR]

Background and aims: DNA-based methods present new opportunities for overcoming the difficulties of accurately identifying and quantifying roots of different plant species in field soils. In order to quantify species-specific root biomass from measurements of DNA, consideration needs to be given to replication and ability to recover roots for calibration purposes in order to account for spatial, temporal and inter- and intra-species variation in DNA content of roots and distribution of roots within the soil profile. Methods: This paper develops the field application of a DNA-based technique for direct quantification of roots in soils. The method was applied to a field experiment to investigate differences in root growth of acid-soil resistant and sensitive genotypes of perennial pasture grasses in an acid soil. DNA was extracted directly from soil and species-specific DNA was quantified using quantitative real-time PCR prior to estimation of root biomass. Results: Root growth of the perennial grasses was quantified using the DNA-based technique, although separate calibration procedures were needed to convert DNA content to root mass for each species, soil layer and sampling date. Compared to acid-soil resistant genotypes, lesser root growth in acid soil layers and reduced above-ground dry matter production was observed for acid-soil sensitive genotypes. Conclusions: The DNA-based method allowed genotypic differences in root growth to be assessed directly in soil and was advantageous for rapid processing of a large number of samples. However, high replication was still required to overcome spatial variability and separate calibrations were required for different species and soil depths across sampling times. The technique demonstrated greater root growth of acid-soil resistant perennial grasses which was beneficial for their establishment and persistence. [ABSTRACT FROM AUTHOR]

Phosphorus (P)-deficiency is a significant challenge for agricultural productivity on many highly P-sorbing weathered and tropical soils throughout the world. On these soils it can be necessary to apply up to five-fold more P as fertiliser than is exported in products. Given the finite nature of global P resources, it is important that such inefficiencies be addressed. For low P-sorbing soils, P-efficient farming systems will also assist attempts to reduce pollution associated with P losses to the environment. P-balance inefficiency of farms is associated with loss of P in erosion, runoff or leaching, uneven dispersal of animal excreta, and accumulation of P as sparingly-available phosphate and organic P in the soil. In many cases it is possible to minimise P losses in runoff or erosion. Uneven dispersal of P in excreta typically amounts to ~5% of P-fertiliser inputs. However, the rate of P accumulation in moderate to highly P-sorbing soils is a major contributor to inefficient P-fertiliser use. We discuss the causal edaphic, plant and microbial factors in the context of soil P management, P cycling and productivity goals of farms. Management interventions that can alter P-use efficiency are explored, including better targeted P-fertiliser use, organic amendments, removing other constraints to yield, zone management, use of plants with low critical-P requirements, and modified farming systems. Higher productivity in low-P soils, or lower P inputs in fertilised agricultural systems can be achieved by various interventions, but it is also critically important to understand the agroecology of plant P nutrition within farming systems for improvements in P-use efficiency to be realised. [ABSTRACT FROM AUTHOR]

It is unclear whether roots of acid-soil resistant plants have significant advantages, compared with acid-soil sensitive genotypes, when growing in high-strength, acid soils or in acid soils where macropores may allow the effects of soil acidity and strength to be avoided. The responses of root growth and morphology to soil acidity, soil strength and macropores by seedlings of five perennial grass genotypes differing in acid-soil resistance were determined, and the interaction of soil acidity and strength for growth and morphology of roots was investigated. Soil acidity and strength altered root length and architecture, root hair development, and deformed the root tip, especially in acid-soil sensitive genotypes. Root length was restricted to some extent by soil acidity in all genotypes, but the adverse impact of soil acidity on root growth by acid-soil resistant genotypes was greater at high levels of soil strength. Roots reacted to soil acidity when growing in macropores, but elongation through high-strength soil was improved. Soil strength can confound the effect of acidity on root growth, with the sensitivity of acid-resistant genotypes being greater in high-strength soils. This highlights the need to select for genotypes that resist both acidity and high soil strength. [ABSTRACT FROM AUTHOR]

Perennial pasture species are important for sustainable pasture systems; yet some species display poor persistence on acid soils. This work investigated the effect of soil acidity on primary root length and root-hair and rhizosheath development of five perennial grass genotypes varying in acid-soil resistance. Plants were grown in three low-P acid soils that were limed (CaCO) to modify soil pH (0.01 M CaCl extractable) from <4.3 to >5.0 and Al concentrations from ≥ 16 to <4 mg kg (0.01 M CaCl extractable). Root morphology of tall wheatgrass ( Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C Wang), phalaris ( Phalaris aquatica L.), cocksfoot ( Dactylis glomerata L.) and weeping grass ( Microlaena stipoides Labill. R. Br.) was assessed after 20–25 days growth. The root length of tall wheatgrass and phalaris cv Sirosa was sensitive to acidity, with lateral root length more sensitive to acidity than seminal root length. Lime increased the root-hair length and density of both acid-soil sensitive and resistant genotypes (cocksfoot and an acid-resistant line of phalaris) and root-hair length was positively correlated to an increase in rhizosheath size per unit root length. Restricted root length and poor root-soil contact of acid-soil sensitive genotypes may explain their low yield and relatively poor persistence on acid soils. The improvement to root-hair and rhizosheath development of genotypes that are acid-soil resistant in terms of root length demonstrates the benefit of using resistant genotypes in conjunction with liming to manage acid soils. Weeping grass was exceptional in its ability to maintain root length, root-hair and rhizosheath development in acid soil. [ABSTRACT FROM AUTHOR]

Phalaris aquatica L. (phalaris) is a cool-season perennial grass originating from the Mediterranean Basin, north-west Africa and Middle Eastern regions that is used for livestock agriculture mainly in temperate areas with dry summers. It has been the subject of breeding programs in Australia, South America, New Zealand and the USA. Increased knowledge of relationships between wild and cultivated germplasm through use of molecular markers has the potential to facilitate future breeding gains. For this purpose, we conducted an analysis of P. aquatica by using 3905 polymorphic DArTseq SNP markers. Genetic diversity as measured by expected heterozygosity was similar for wild (HE = 0.14; n = 57) and cultivated (HE = 0.13; n = 37) accessions. Diversity in wild germplasm was generally continuous in nature, largely related to geographical location, with a division at the broadest scale into eastern and western clades, with more admixture in the western than the eastern clade. Structure analysis of wild germplasm indicated six subpopulations consistent with country of origin, with some admixture among subpopulations likely resulting from natural and human influences. There were nine subpopulations among wild and cultivated accessions combined. This population structure should be considered if genomic selection is applied in P. aquatica. Analysis of molecular variance indicated that 71% of the genetic variation occurred within subpopulations and 29% among subpopulations. Genetic distances were low among cultivated germplasm from most countries except the USA, which was more distinct. Evaluation of material from the US pool by breeding programs in other countries, and additional material from the less utilised eastern clade, may be worthwhile. Knowledge of genetic diversity is important for traditional and genomics-based breeding in the perennial pasture grass Phalaris aquatica. Use of molecular markers indicated the presence of nine groups among wild and cultivated germplasm, with close relationships among cultivars from most countries where P. aquatica is bred. Population structure should be considered for genomic breeding of P. aquatica and more testing of germplasm from less exploited germplasm groups may be worthwhile in future breeding. [ABSTRACT FROM AUTHOR]

In recent decades several pasture legumes have been available in southern Australia as potential alternatives to the most widely used annual pasture legume Trifolium subterraneum. Little is known about their soil phosphorus (P) requirements, but controlled environment experiments indicate that at least some may differ in their P fertiliser requirements. In this study, pasture legume varieties, including T. subterraneum as the reference species, were grown at up to four sites in any one year over a 3-year period (in total, seven site × year experiments) to measure herbage growth responses in spring to increased soil P availability. A critical soil test P concentration (corresponding to 95% maximum yield) was estimated for 15 legumes and two pasture grasses. The critical soil P requirements of most of the legumes did not differ consistently from that of T. subterraneum , indicating their soil fertility management should follow the current soil test P guidelines for temperate Australian pastures. However, the critical P requirement of Medicago sativa was higher than that of T. subterraneum , but remains ill-defined because extractable soil P concentrations in these experiments were often not high enough to permit a critical P estimate. Three forage crop legumes (Trifolium incarnatum , Trifolium purpureum , Trifolium vesiculosum) and two pasture legumes (Ornithopus compressus , Ornithopus sativus) had lower critical soil test P concentrations. It may be feasible to manage pastures based on these species to a lower soil test P benchmark without compromising yield. Extractable phosphorus concentrations of soil corresponding to near-maximum pasture legume growth can be used as benchmarks for soil phosphorus management in temperate grass–legume pastures. In this study, the soil phosphorus requirements of alternative pasture legumes used in southern Australia were assessed and compared with that of the widely used legume Trifolium subterraneum. The results indicate that published soil test phosphorus benchmarks for T. subterraneum are appropriate for many alternative legumes, but also demonstrate that some can be fertilised to lower benchmark concentrations without compromising yield. [ABSTRACT FROM AUTHOR]

Background and aims: This work aimed to quantify the critical external requirement for phosphorus (P) (i.e. extractable-P concentration required for 90 % of maximum yield) for a number of temperate legume species and understand differences in dry matter allocation, P distribution and P acquisition efficiency among these species. Methods: Shoot and root growth of five legume and one grass species was assessed in response to six rates of P mixed into the top 45 mm of soil in a pot experiment. Dactylis glomerata and Trifolium subterraneum were used as benchmark species; they are commonly grown together in mixed temperate pastures and have low and high critical external requirements for P, respectively. Growth was compared with four alternative legume species: Ornithopus compressus, Ornithopus sativus, Biserrula pelecinus and Trifolium hirtum, that have root morphologies better suited to soil exploration and nutrient acquisition than that of Trifolium subterraneum. Results: Dactylis glomerata, Ornithopus compressus and Ornithopus sativus had maximum yields equal to or greater than Trifolium subterraneum but achieved this at rates of P less than half that of Trifolium subterraneum. Biserrula pelecinus and Trifolium hirtum had critical P requirements between that of Trifolium subterraneum and the Ornithopus species, but also had lower yields. Root dry matter of Dactylis glomerata and the Ornithopus species in the fertilised soil layer was only marginally changed in response to low P supply. In contrast, Trifolium subterraneum, Trifolium hirtum and to a lesser extent Biserrula pelecinus markedly increased root dry matter allocation to this soil layer. Species with lower critical P requirements were able to take up more P per unit root dry mass than those with higher critical P requirements, particularly at lower levels of P addition. Conclusions: The high P acquisition efficiencies of the Ornithopus species and Dactylis glomerata were likely to have contributed to their low critical external P requirements. It was surmised that differences in root morphology traits underpin the differences in acclimation to low P stress and P acquisition efficiency among the species. [ABSTRACT FROM AUTHOR]

Annual pasture legume species can vary more than 3-fold in their critical external phosphorus (P) requirement (i.e. P required for 90% of maximum yield). In this work we investigated the link between root morphology, P acquisition and critical external P requirement among pasture species. The root morphology acclimation of five annual pasture legumes and one grass species to low soil P availability was assessed in a controlled-environment study. The critical external P requirement of the species was low (Dactylis glomerata L., Ornithopus compressus L., Ornithopus sativus Brot.), intermediate (Biserrula pelecinus L., Trifolium hirtum All.) or high (Trifolium subterraneum L.). Root hair cylinder volumes (a function of root length, root hair length and average root diameter) were estimated in order to assess soil exploration and its impact on P uptake. Most species increased soil exploration in response to rates of P supply near or below their critical external P requirement. The legumes differed in how they achieved their maximum root hair cylinder volume. The main variables were high root length density, long root hairs and/or high specific root length. However, total P uptake per unit surface area of the root hair cylinder was similar for all species at rates of P supply below critical P. Species that maximised soil exploration by root morphology acclimation were able to prolong access to P in moderately P-deficient soil. However, among the species studied, it was those with an intrinsic capacity for a high root-hair-cylinder surface area (i.e. long roots and long root hairs) that achieved the lowest critical P requirement. [ABSTRACT FROM AUTHOR]

Aims: The legumes most often used in temperate pastures such as Trifolium subterraneum have relatively high external P requirements for maximum growth. We investigated root traits associated with P acquisition in current and novel pasture legumes, as well as temperate grasses which have lower P requirements. Methods: Thirteen legume species, two pasture grasses, and three high carboxylate-exuding crop species ( Lupinus albus, L. angustifolius, Cicer arietinum) were grown in a glasshouse for six weeks. Rhizosphere carboxylates and root morphological traits were measured. Results: Ornithopus spp. had rhizosphere carboxylates in similar quantities to the Lupinus spp. (> 40 μmol g root dry mass) . Trifolium subterraneum lines had relatively large average root diameter, reduced specific root length and very short average root hair length resulting in specific root hair cylinder volumes (RHCVs) only 14-20 % of the grasses. However, O. sativus, O. compressus and Biserrula pelecinus had specific RHCVs more comparable to the grasses. Conclusions: Novel pasture legume species with root morphology more comparable to that of grasses than T. subterraneum were identified. Of these, Ornithopus spp. were notable as they also had high rhizosphere carboxylates relative to root dry mass. [ABSTRACT FROM AUTHOR]

Development of more phosphorus (P)-efficient pasture legumes could improve the P balance of pasture systems. Trifolium subterraneum (subterranean clover) is the most widely-grown annual pasture legume in southern Australia and is host to arbuscular mycorrhizal fungi (AMF). To examine the potential to alter colonisation level through breeding, 97 lines from the core collection of subterranean clover (core lines) and 42 cultivars (cultivar lines) were grown in a glasshouse in a low-P sandy acid field soil with indigenous AMF (Experiment 1). To examine the robustness of rankings, two cultivars (Riverina and Woogenellup) were also grown in 11 field soils (Experiment 2). To examine whether the presence of AMF changed other root traits important for P uptake, cultivars Riverina and Woogenellup were grown in two low-P field soils (sand, sandy loam), either pasteurised to remove indigenous AMF or unpasteurised, and with and without addition of inoculum of AMF (Experiment 3). The range of colonisation for core lines and cultivar lines was similar (∼12–68% of root length), however, the core lines had higher mean colonisation (37% vs 33%) and a greater proportion of lines with >40% of root length colonised (41% vs 24% of lines). Woogenellup was more heavily colonised than Riverina in eight soils and had a similar level of colonisation in three soils. In the sand, pasteurisation resulted in shoot DM increasing by up to 100% (possibly due to reduction in root diseases). Inoculation, in pasteurised and unpasteurised soil, resulted in an increase in shoot DM, shoot P concentration and shoot P content of ∼100%, increased average root diameter by up to 13%, decreased specific root length by up 30% and decreased root mass ratio; effects on average root hair length were variable. In the unpasteurised sandy loam, shoot P concentrations were higher than in the sand, and inoculation slightly increased shoot P concentration, but not shoot DM; the effects of inoculation on root traits were mostly small. We conclude that potential may exist to select subterranean clover for higher or lower colonisation by AMF using cultivar lines. Also, indigenous AMF may be less effective at enhancing plant P uptake and growth than inoculants. Finally, key root traits for enhancing plant P-uptake may change in the presence of AMF, but not sufficiently so to warrant deliberate inclusion or exclusion of AMF when screening germplasm for such traits. [ABSTRACT FROM AUTHOR]

Background: Agricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. In fertilised and intensive systems, P-efficient plants are required to minimise inefficient use of P-inputs and to reduce potential for loss of P to the environment. Scope: Three strategies by which plants and microorganisms may improve P-use efficiency are outlined: (i) Root-foraging strategies that improve P acquisition by lowering the critical P requirement of plant growth and allowing agriculture to operate at lower levels of soil P; (ii) P-mining strategies to enhance the desorption, solubilisation or mineralisation of P from sparingly-available sources in soil using root exudates (organic anions, phosphatases), and (iii) improving internal P-utilisation efficiency through the use of plants that yield more per unit of P uptake. Conclusions: We critically review evidence that more P-efficient plants can be developed by modifying root growth and architecture, through manipulation of root exudates or by managing plant-microbial associations such as arbuscular mycorrhizal fungi and microbial inoculants. Opportunities to develop P-efficient plants through breeding or genetic modification are described and issues that may limit success including potential trade-offs and trait interactions are discussed. Whilst demonstrable progress has been made by selecting plants for root morphological traits, the potential for manipulating root physiological traits or selecting plants for low internal P concentration has yet to be realised. [ABSTRACT FROM AUTHOR]