Grassland agriculture is an important industry for livestock production and land management throughout the world. We review the principles of nutrient cycling in grassland agriculture, discuss ...examples of grassland farming systems research, and demonstrate the usefulness of whole-farm simulation for integrating economic and environmental components. Comprehensive studies conducted at the Karkendamm experimental farm in northern Germany and the De Marke experimental farm in the Netherlands have quantified nutrient flows and developed innovative strategies to reduce nutrient losses in grassland farming systems. This research has focused on improving the utilization of manure nutrients on the farm by including grain crops in cropping systems with grassland and by incorporating manure handling techniques that reduce nitrogen losses. Although the information generated in experimental farms is not always directly applicable to other climates and soils, it is being transferred to other regions through computer simulation. A whole-farm model calibrated and verified with the experimental farm data is being used to evaluate and refine these strategies for commercial farms in other areas. Simulation of farms in northern Europe illustrate that on the sandy soils of this region, maize (Zea mays L.) silage can be used along with grasslands to increase farm profitability while maintaining or reducing nutrient loss to the environment. Use of cover crops, low emission barns, covered manure storages, and direct injection of manure into soil greatly reduces N losses from these farms, but their use creates a net cost to the producer. By integrating experimental farm data with whole-farm simulation, more sustainable grassland production systems can be cost-effectively evaluated, refined, and transferred to commercial production.
The response of pea embryonic tissues to the replication of a range of different viruses was investigated using in situ hybridization to analyze changes in the expression of two host genes, heat ...shock protein 70 (hsp70) and lipoxygenase (lox1). Excised pea embryos were infected using microprojectile bombardment with a nonseed transmissible strain of Pea seed-borne mosaic potyvirus, or with Pea early browning tobravirus (PEBV), White Clover mosaic potexvirus, or Beet curly top geminivirus. Collectively, these examples represent families of viruses with differing genomic features, differing numbers of genomic components and differing replication strategies. In all cases, there was an induction of hsp70 associated with virus replication and, in most cases, a downregulation of lox1. Hence, either each virus has a direct inducer of these common responses or the induction is indirectly the result of a generic feature of virus infection. By exploiting the bipartite nature of the PEBV genome, the coat protein gene and genes involved in vector transmission were excluded as potential inducers.
Two-week-old
Phaseolus vulgaris plants, wick-fed with 1 mmol/L salicylic acid (SA) or 50 nmol/L dihydrozeatin (DHZ), showed partial inhibition of the accumulation of white clover mosaic virus (WClMV) ...in infected primary leaves. This inhibition was measured as a decrease in the accumulation of both viral mRNA and viral coat protein, especially at the early stages of infection. Salicylic acid treatment resulted in moderately increased expression of phenylalanine ammonia lyase (
PAL),
NPR1, PR1 and
HSP70 genes that participate in resistance to pathogens in plants. In contrast, DHZ treatments did not induce significant changes in expression of these genes. The expression of the
P. vulgaris alternative oxidase (
AOX) gene homolog, an enzyme implicated in plant resistance to viruses, showed low constitutive expression during the first 11 days post-infection and was not affected by either SA or DHZ. It appears that, while SA induced the NPR1-PR1 pathogen defense pathway genes, both SA and DHZ may use a different pathway to induce resistance to WClMV infection in
P. vulgaris plants.
One of the most difficult elements of the ecological risk assessment of transgenic plants is investigation of their potential impact on biodiversity in complex non-target communities. This problem is ...particularly acute for pasture plants, since many have a track record of invasiveness. In this paper we develop an understanding of some aspects of the ecology of Trifolium repens L. (white clover) in montane vegetation communities in southeastern Australia as part of a larger project investigating potential ecological risks associated with commercial release of newly-developed transgenic virus-resistant T. repens cultivars. We use a combination of floristic surveys and biomass sampling to determine the habitat affinity of T. repens, the structure and composition of associated communities, and the scale at which different abiotic and biotic factors correlate with T. repens abundance. We also compare the abundance of native and exotic species within specific morpho-functional groups and use this to determine the relative significance of T. repens as a community constituent, and to identify native species that would be most at risk by expanding populations of T. repens. We found that T. repens comprises a relatively small component of the total community cover and biomass, but is one of the most abundant herbaceous species in mesic Poa - dominated grasslands and Poa-Eucalyptus woodlands in the study area, and that T. repens abundance is correlated at the within-community scale primarily with soil moisture and fertility. At smaller scales T. repens is limited by the hierarchical dominance of native graminoids and we conclude that competition for inter-tussock space in mesic communities is the most likely mechanism by which expanding populations of T. repens would influence populations of associated native species. These results have significant implications for the manner in which future analysis and risk quantification stages of the risk assessment of virus-resistant T. repens and other transgenic pasture plants in complex plant communities are performed.
This paper presents the cloning and biochemical characterisation of the cysteine protease Tr-cp 14 from white clover (
Trifolium repens). The predicted amino acid sequence of Tr-cp 14 is 71%, 74% and ...74% identical to the cysteine proteases XCP1 and XCP2 from
Arabidopsis thaliana, and p48h-17 from
Zinnia elegans, respectively. These cysteine proteases have previously been shown to be involved in programmed cell death during tracheary element differentiation. The precursor polypeptide of Tr-cp 14 was expressed in
Escherichia coli, purified from inclusion bodies and refolded. The precursor polypeptide could be processed to its active mature form autocatalytically at pH 5.0 and had a requirement for 20 mM
l-cysteine for optimal activity. Mature Tr-cp 14 showed a preference for synthetic aminomethylcoumarin substrates with either Leu or Phe in the P2 position when tested with Arg in P1. A substrate with Arg in both the P1 and P2 position was not accepted as substrate.
The response of an irrigated perennial ryegrass-white clover pasture to fertiliser nitrogen application rates of 0, 50, 100 and 150 kg N ha
−1
applied in either autumn, early winter, late winter, ...early spring or late spring was investigated over a three-year period. Primary dry matter production (PDM) and residual dry matter production (RDM) were recorded five and ten weeks after fertiliser N application, respectively. PDM responses were determined mainly by fertiliser N application rate. On average the highest PDM was obtained following N applications in spring and lowest when N was applied in early winter. Although RDM production generally also increased with increasing fertiliser N rates, responses were much smaller than those recorded for PDM and were affected by the season of fertiliser N application. The highest RDM was obtained when N was applied in autumn and winter while application in spring had no, or even a negative effect, on RDM. Total dry matter production (PDM+RDM) increased (P<0.05) with increasing N application rates. Except for the 0 kg N ha
−1
treatment in 2002, which recorded lower DM yields compared to fertilised plots, total annual dry matter production of the pasture was not affected by N fertiliser application rate. Nitrogen application can therefore be used to improve dry matter production during a short predetermined period. Although the 150 kg N ha
−1
applied in early and late spring generally gave the best results in terms of PDM, the 50 kg N ha
−1
application treatments resulted in a more efficient conversion of N applied to additional DM produced.
Small-scale dairying is an option for campesinos in Mexico. The costs of feeding are high and strategies based on quality forages are a priority. The performance, agronomic variables and feeding ...costs were evaluated for dairy cows continuously grazing perennial ryegrass-white clover for 9 h/day (PRG) or fed cut herbage from annual ryegrass for 8 weeks followed by 9 h/day for 6 weeks on a tethered rotational grazing pattern (ARG). All cows received 3 kg/day of an 18% crude protein (CP) concentrate. A 14-week split-plot on-farm experiment was designed with 10 cows from two participating farmers, and 1.5 ha per strategy. Milk yield was recorded weekly and milk composition, live weight and body condition score were recorded every 14 days. Net herbage accumulation was greater for ARG (8222 kg organic matter (OM)/ha) than for PRG (5915 kg OM/ha) (p < 0.05), with higher CP in PRG (p < 0.05). Milk yield was 19 kg/cow per day for PRG and 15.9 kg/cow per day for ARG (p > 0.05). Over 14 weeks, PRG produced 1422 kg more milk. There were no differences for live weight or condition score (p > 0.05), but linear regression shows a live weight gain of 0.200 kg/cow per day for PRG. Protein and fat content showed no differences (p > 0.05), but milk fat content in PRG was below standard. ARG had 60% higher costs, and margins were 38% higher in PRG. ARG has a place in rain-fed fields. The results provide viable options for improving these systems that may be suitable in their socio-economic context and their social and personal objectives.
To study phosphorus (P) depletion and soil pH changes at the root-soil interface (rhizosphere) and at the hyphae-soil interface, mycorrhizal and non-mycorrhizal white clover (Trifolium repens L.) ...plants were grown for 7 wk in two sterilized soils (Luvisol and Cambisol) in pots comprising five compartments: a central one for root growth, two adjacent compartments, separated from the central compartment by a nylon net of 30 μm mesh size, for growth of vesicular-arbuscular (VA) mycorrhizal Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe hyphae (hyphal compartments), and two outer compartments, separated from the hyphal compartments by a 0·45 μm membrane, which neither roots nor hyphae could penetrate (bulk soil compartments). Phosphorus was supplied as Ca(H2PO4)2at a rate of 50 mg P kg-1soil in the root compartment and 150 mg P kg-1soil in the hyphal and bulk soil compartments. Nitrogen was supplied as (NH4)2SO4at the rate of 300 mg N kg-1soil uniformly to all compartments. In both soils, shoot dry weight and P uptake were much higher in mycorrhizal plants compared with nonmycorrhizal plants. Hyphae of VA mycorrhizal fungi contributed 70% (Cambisol) or 80% (Luvisol) to total P uptake of mycorrhizal plants. In the hyphal compartments, concentrations of both H2O-extractable soil P (Cambisol and Luvisol) and NaHCO3-extractable soil P (Luvisol) were decreased drastically. Soil P depletion profiles developed not only at the root-soil interface (rhizosphere), but also at the hyphae-soil interface and extended several millimetres from the hyphae surface into the soil. Likewise, the soil pH was decreased at the root-soil interface, in the hyphal compartment and also at the hyphae-soil interface. The results demonstrate that, similarly to roots, hyphae of VA mycorrhizal fungi have the ability to form a P depletion zone and a zone of altered pH in the adjacent soil. Thus, as well as at the root-soil interface, soil conditions at the hyphae-soil interface may also differ considerably from conditions in the bulk soil.
We report the molecular structure, genomic organization, chromosomal distribution and evolutionary dynamics of TrR350, a satellite DNA isolated from the forage legume white clover (Trifolium repens ...L.; 2n = 4 x = 32). The basic repeating unit is an A+T rich 350 bp Hin dIII fragment with a complex dimeric structure consisting of an internal direct repeat of 156 bp packed between unrelated flanking sequences. Each 156 bp repeat has a conserved 24 bp motif repeating at two places. Most of the 24 bp short repeating units enclose a pentanucleotide CAAAA motif, presumed to be involved in breakage-reunion mechanism of tandemly repeating arrays. The dimers share high sequence homology among themselves while monomers within dimers show significant sequence divergence. Genomic Southern hybridization and/or fluorescence in situ hybridization (FISH) on 17 Trifolium species/subspecies revealed that it is a lineage-specific repeat confined to several species within the section Lotoidea originating in the Mediterranean region. The uniform length of the basic repeating unit and the centromeric localization in most of the species harbouring it reflects its extensive conservation in the lineage. However, the Hin dIII restriction profile in seven species also indicated independent evolution of this repeat.
The study was conducted to evaluate the effect of soil on early growth of three white clover (Trifolium repensL.) cultivars obtained from three different countries and to examine relationships ...between pre-screened traits of seedlings and traits of three month old plants. Pre-screening for germination, temperature and pH tolerance indicated that temperature and pH decrease significantly influenced on germination and seedling growth of cultivars. In conditions of spring temperatures higher than average soil substrate and two different soils collected from a different source plots influenced on emergence, plant width, internode length of stolon, leaf number, leaf-petiole weight and stolon weight of clovers. Pre-screened germination energy and germination were significantly correlated with emergence, plant height, internode length of stolon, petiole length and flower number of three month old plants.
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