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Context: Reliable seed production is a key requirement for successful year-on-year regeneration of annual pasture legumes. Aims: The study aims were to investigate the developmental patterns of flowers and pods and the effect on seed number among cultivars of French (Ornithopus sativus Brot.) and yellow serradella (O. compressus L.); and to assess the effects of early flower loss. Methods: Four cultivars of each species were grown in a glasshouse under non-limiting growth conditions. Date of flowering and numbers of flowers, pods and seeds were assessed for up to 20 reproductive nodes on two stem axes per plant (n = 5 plants). A flower removal treatment was imposed to assess whether early flower loss affected flower and/or pod production. Key results: Flowering in the serradellas was indeterminate, but for all cultivars there was a peak period of flower and pod production, with the timing and duration of the peak period differing among cultivars. Peak flowering occurred primarily because the proportion of plants flowering began to decline, but the number of flowers per reproductive node and the number of pods formed per node also declined with time. Compensation for early flower loss was observed for most cultivars because of a longer duration of pod formation and/or greater numbers of pods developed on higher reproductive nodes. Conclusions: This study demonstrated that there is diversity in the patterns of flowering and podding and number of seeds initiated among serradellas. Implications: Diversity in flowering and podding patterns combined with a capacity to compensate for early flower loss may be used to develop serradellas better able to cope with environmental stressors (frost, drought, heat) experienced during the flowering window. To ensure the continued existence of annual legume species in temperate regions, it is essential to understand the factors contributing to successful seed production; for instance, certain cultivars of French and yellow serradella occasionally flower at suboptimal times, potentially leading to reduced seed production. This study uncovered differences in how these cultivars produce flowers, pods and seeds. Some showed the ability to adapt to early flower loss, suggesting that selective breeding could improve seed yield resilience. [ABSTRACT FROM AUTHOR]

Context: Opportunity exists to expand serradella (Ornithopus spp.) use onto heavier, duplex soil types in permanent pasture environments of south-eastern Australia. This requires cultivars with appropriate flowering times and flowering-date stability (i.e. flowering at the same date in spring regardless of timing of the autumn break). Aim: This work examined evidence of variation in flowering date and flowering-date stability in the NSW southern tablelands for a widely-used French serradella (O. sativus) cv. Margurita. Methods: Seed (sourced from a commercial supplier) was sown 21 March 2019 (Canberra, ACT) and 231 individual plants were monitored for time to first flower. A subset of plants exhibiting 'early' or 'late' flowering were identified and their seeds collected. In 2020, seed from ~15 plants from each selection was sown in Canberra in late March and early May to represent an 'early' and a 'later' break of season (n = 3). Key results: In the early-sown treatment, 'early-flowering' selections typically reached the median date of first flower (50%-flowering) from mid- to late August, while 'late-flowering' selections reached 50%-flowering early- to mid-September. When sown later, the 'early-flowering' selections began flowering from mid- to late September, while the 'late-flowering' selections flowered mid-September to early October. The 'early' selections exhibited greater flowering-date instability than 'late' selections and flowered particularly early when sown early. This indicated diversity within cv. Margurita for flowering-time control (e.g. vernalisation and/or photoperiod requirements). Implications: Evaluating cultivars of serradellas for flowering date and flowering date stability in their target environment(s) is essential to ensure cultivars are suitably adapted to these environments. Serradellas (Ornithopus spp.) are a novel legume option for the permanent pasture environments of south-eastern Australia. This paper investigated evidence of variation in flowering time characteristics within a widely used cultivar of French serradella. We recommend that new cultivars of serradellas be evaluated for flowering time characteristics in their target environment(s) to assess whether the cultivars are suitably adapted to these environments. This is essential to maximise production, feeding value and facilitate effective grazing management. [ABSTRACT FROM AUTHOR]

Context: There is interest in using serradella (Ornithopus spp.) in permanent pastures of the high rainfall zone of south-eastern Australia. However, there is little information concerning levels of hardseededness or patterns of seed softening in these environments. Aim: This study quantified seed softening of serradella species in comparison with subterranean clover (Trifolium subterraneum L.) in the Southern Tablelands and Central Slopes districts of eastern Australia. Methods: Mature seeds were placed in mesh pouches on the soil surface and were retrieved periodically to assess residual hard seed proportions throughout the growing season(s) in four experiments conducted over 2018 and 2019. Key results: Patterns of seed softening among adapted cultivars of subterranean clover were consistent: initially high proportions of hard seed, followed by rapid softening from mid-summer to the end of autumn with the remnant portion of seeds remaining hard. In contrast, diverse patterns of seed softening were observed among serradella cultivars, ranging from highly soft-seeded through to high initial hard seed portions that either softened rapidly or softened over a lengthy period. Rates of seed softening were faster in the warmer/drier environment of Cowra compared to the wetter/cooler environment of Canberra. Conclusions: The study revealed seed softening patterns among serradellas to be diverse and different to subterranean clover. This will affect management and suitability of serradella cultivars for permanent pastures. Implications: In permanent pastures, serradellas that soften slowly over several years are likely to have limited regeneration in the year after pasture establishment with a high potential for weed invasion. Serradella has many advantages as a pasture legume, however persistence and productivity in permanent pastures can be inadequate. This study quantified seed softening of serradella species in comparison with subterranean clover in the Southern Tablelands and Central Slopes districts of eastern Australia. Diverse patterns of seed softening were observed among serradella cultivars, in contrast to subterranean clover. Implications for pasture establishment of serradella in high rainfall zone permanent pastures is discussed. [ABSTRACT FROM AUTHOR]

Differences in root morphology and acclimation to low‐phosphorus (P) soil were examined among eight legume species from the Trifolium Section Tricocephalum to understand how these root attributes determine P acquisition. Ornithopus sativus was included as a highly P‐efficient benchmark species. Plants were grown as microswards in pots with five rates of P supplied in a topsoil layer to mimic uneven P distribution within a field soil profile. Topsoil and subsoil roots were harvested separately to enable measurement of the nutrient‐foraging responses. Critical P requirement (lowest P supply for maximum yield) varied over a threefold range, reflecting differences in root morphology and acclimation of nutrient‐foraging roots to P stress. Among the species, there was a 3.2‐fold range in root length density, a 1.7‐fold range in specific root length, and a 2.1‐fold range in root hair length. O. sativus had the lowest critical P requirement, displayed a high root length density, the highest specific root length, and the longest root hairs. Acquisition of P from P‐deficient soil was facilitated by development of a large root hair cylinder (i.e. a large root–soil interface). This, in turn, was determined by the intrinsic root morphology attributes of each genotype, and the plasticity of its root morphology response to internal P stress. Root acclimation in low‐P soil by all species was mostly associated with preferential allocation of mass to nutrient‐foraging roots. Only O. sativus and four of the Trifolium species adjusted specific root length beneficially, and only O. sativus increased its root hair length in low‐P soil. [ABSTRACT FROM AUTHOR]

Background and aims: The growth and root morphology responses to soil phosphorus (P) fertility by five cultivars of Trifolium subterraneum (a temperate annual pasture legume) were examined to assess whether differences in root morphology and/or root acclimation to P stress influenced P-acquisition by the clover varieties, or their critical P requirements (i.e. the rate of P supply needed for maximum shoot yield).Methods: The clovers were grown as microswards in soil with P stratified in a topsoil layer to mimic growth conditions and soil P availability in a pasture. Yield and P content of shoots, and roots from the topsoil and subsoil layers was determined after 5 weeks growth in a controlled-environment cabinet. The lengths, diameters, and root hair lengths of nutrient foraging roots from the topsoil layer were quantified.Results: The shoot yield of the cultivars was similar when grown with high soil P fertility. However, the cultivars varied up to 1.5-fold in their ability to yield at low levels of soil P supply, and by 1.6-fold in their critical P requirements. All cultivars acclimated to low P soil by increasing root length density in the topsoil but those that yielded relatively well did so by maintaining a large root hair cylinder volume (i.e. they explored more soil) under low soil P conditions. This was associated with maintenance of dry matter allocations to topsoil roots and higher specific root lengths. Both factors assisted development of high root length density for nutrient foraging. Root acclimation responses to P were compared among the cultivars at equivalent relative shoot yields to assess the influence of plant P stress as a trigger for nutrient foraging. The least P-efficient cultivars slowed their allocation of dry matter to foraging roots at lower levels of P stress.Conclusions: The results suggest variation within T. subterraneum for root proliferation and specific root length could be targeted in breeding for improved P-acquisition efficiency. [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]