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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 58 (2003), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Daily net canopy photosynthesis (Pn) of cocksfoot (Dactylis glomerata L.) was predicted for combinations of temperature, herbage nitrogen (N) concentration and water status from the integration of models of leaf photosynthesis of the light-saturated photosynthetic rate (Pmax), photosynthetic efficiency (α) and the degree of curvature (θ) of leaf light-response curves. The effect on Pn, maximum Pn (Pn max) and the optimum leaf area index (LAI at Pn max) was examined when any one of these factors was limiting. The ranges that gave the optimum values of Pn (Pn max = 30·8–33·5 g CO2m−2 d−1) for temperature (19–22°C) and N concentration (40–50 g N kg−1 DM) were smaller than those for net leaf photosynthesis. Also, Pn fell to 0 at a lower level of water stress (pre-dawn leaf water potential, ψlp = −12·5 bar) than for Pmax. The canopy photosynthesis model was then used to compare predicted and measured dry matter (DM) production for cocksfoot pastures grown under a diverse range of environmental conditions with field data from New Zealand and Argentina. To predict DM production leaf area index and leaf canopy angle were included from field measurements. The model explained about 0·85 of the variation in cocksfoot DM production for the range of 6·5–134 kg DM ha−1 d−1. The canopy model overestimated the DM production by 0·10 which indicates that a further Pmax function for leaves of different ages and a partitioning sub-model may be needed to improve predictions of DM production.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 57 (2002), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Maximum light-saturated photosynthetic rate (Pmax) and stomatal conductance (gs) of field-grown cocksfoot (Dactylis glomerata L.) leaves in a silvopastoral system were measured at different times under moderate (850–950 µmol m−2 s−1 photosynthetic photon flux density, PPFD) and severe shade (85–95 µmol m−2 s−1 PPFD). Also Pmax and gs were measured after 30, 60 and 180 min of severe shade to determine the lag in the rise of photosynthesis rate from low to high irradiance levels (induction state). The highest Pmax and gs values obtained were 26·5 µmol CO2 m−2 s−1 and 0·41 mol H2O m−2 s−1 in non-limiting conditions with full sunlight (1900 µmol m−2 s−1 PPFD). These values were defined as standardized dimensionless Pmaxs=1 and gss=1 for comparison of treatment effects. The Pmaxs under severe shade decreased by 0·004 units per minute from 1 to 180 min and reached a steady-state of 0·37 units after 140 min. Under moderate shade, Pmaxs decreased by 0·002 units per minute from 1 to 120 min and reached a steady-state of 0·76 units. The time required to reach full induction on return to full sun (Pmaxs=1) was 15 min after 30 min of severe shade and 37 min after 180 min of shade. Mathematical equations were derived to describe the changes in Pmaxs and gss under severe and moderate shade and during induction. The rate of change of gss was slower than for Pmaxs on entering shade and also slower during the subsequent induction process. This indicated other factors in addition to gs were operating in the reduction and increment of Pmax and a two-step model to explain this is proposed. The defined photosynthetic responses of cocksfoot leaves to fluctuating light regimes could be used to develop quantitative predictions of Pmax for inclusion in a canopy photosynthesis model of silvopastoral systems.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A simple multiplicative model using temperature, foliage nitrogen (N) concentration and water status was developed to predict the maximum photosynthetic rate (Pmax) of field-grown cocksfoot (Dactylis glomerata L.) leaves when none, one, two or all the factors were limiting. The highest Pmax was 27·4 μmol CO2 m–2 s−1 in non-limited conditions, which was defined as the standardized Pmax value dimensionless (Pmaxs=1). Pmaxs increased 0·058 units per °C from 10°C to the optimum range (19–23°C) (Pmaxs=1) and then declined 0·077 units of Pmaxs per °C from 23 to 31°C. Pmaxs=1 was also measured from 59 to 52 g N kg−1 dry matter (DM) foliage N. Pmaxs then decreased at the rate of 0·115 units per 10 g N kg−1 DM from 52 to 26 g N kg−1 DM, and 0·409 units of Pmaxs per 10 g N kg−1 DM from 26 to 15 g N kg−1 DM. For predawn leaf water potential (ψlp), Pmaxs=1 was measured from −0·1 to −1·2 bar but declined linearly at a rate of 0·078 units per bar of ψlp from −1·2 to −14·0 bar because of a linear decrease in stomatal conductance. An interaction between low N content (≤20 g N kg−1 DM) and high temperature (〉23°C) was also detected. Together, this multiplicative model accounted for 0·82 of the variation in Pmaxs.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 121 (2002), S. 0 
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Ascochyta blight, caused by Ascochyta lentis, is one of the most globally important diseases of lentil. Breeding for host resistance has been suggested as an efficient means to control this disease. This paper summarizes existing studies of the characteristics and control of Ascochyta blight in lentil, genetics of resistance to Ascochyta blight and genetic variations among pathogen populations (isolates). Breeding methods for control of the disease are discussed. Six pathotypes of A. lentis have been reported. Many resistant cultivars/lines have been identified in both cultivated and wild lentil. Resistance to Ascochyta blight in lentil is mainly under the control of major genes, but minor genes also play a role. Current breeding programmes are based on crossing resistant and high-yielding cultivars and multilocation testing. Gene pyramiding, exploring slow blighting and partial resistance, and using genes present in wild relatives will be the methods used in the future. Identification of more sources of resistance genes, good characterization of the host-pathogen system, and identification of molecular markers tightly linked to resistance genes are suggested as the key areas for future study.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-203X
    Keywords: Key words Agrobacterium rhizogenes ; Brassica oleracea ; Transformation ; Arginine ; Acetosyringone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  An improved broccoli transformation system was developed by optimising several factors that affect the rate of effective Agrobacterium-mediated transformation. Leaf explants of cultivar Shogun were co-cultivated with Agrobacterium rhizogenes strain A4T harbouring the binary vector pART278. The T-DNA of this binary vector contains a neomycin phosphotransferase II (NOS-NPTII-NOS) gene for kanamycin resistance and a β-glucuronidase (35S-GUS-OCS) gene. Several media and factors were evaluated including combinations of arginine, mannopine, acetosyringone and the use of feeder cell layers. The new protocol includes the use of 200 μm acetosyringone in LB medium for bacterial growth, the use of a Brassica campestris feeder cell layer, 10 mm mannopine and 50 μm acetosyringone in the co-cultivation medium and 1 mm arginine in the selection medium. The use of this optimised protocol produced transformation rates of 33% in preliminary experiments transforming broccoli with the antisense 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene from pTOM13.
    Type of Medium: Electronic Resource
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