James H. Macduff

Genetic Improvement of Forage Species to Reduce the Environmental Impact of Temperate Livestock Grazing Systems

Abberton, M. T., Marshall, A. H., Humphreys, M. W., Macduff, J. H., Collins, R. P., Marley, C. L. (2008). Genetic improvement of forage species to reduce the environmental impact of temperate livestock grazing systems. Advances in Agronomy, 98, 311-355.

Characterization of novel inbred lines of white clover (Trifolium repens L.). I. Dynamics of plant growth and nodule development in flowing solution culture

Growth, dry matter partitioning between shoots and roots, and extent of nodulation were characterised in four novel self-fertile highly inbred lines (referred to as A, B, C and D) of white clover (Trifolium repens L.) thought to differ fundamentally in their nitrogen relations and therefore regarded as candidate material for genetic mapping. Plants were inoculated with a mixture of three strains of Rhizobium and grown in flowing nutrient solutions without N for 18 d. Half the plants were then supplied with 20 μM NO3- during a 36 d treatment period, the remaining plants acting as ‘controls’ solely dependent upon N2 fixation for acquisition of N. Total dry matter production and shoot:root ratios were similar in all lines supplied with NO3- and in control plants of lines B and C. Growth was severely reduced in control plants of line D and to a lesser extent in control line A. These effects were attributed to a failure to develop effective N2 fixation capacity after apparently normal infection. Mean nodule size, nodule numbers and nodule d.w. per plant were extremely low in line D compared with the other lines, irrespective of whether NO3- was supplied. Lines A, B and C differed in the severity with which NO3- decreased mean d.w. per nodule and total nodule d.w. per plant relative to corresponding control plants, with line C being least sensitive. Nitrate also decreased the total number of nodules per plant relative to control plants after day 14 in all lines except C, and most severely in line B.

Varietal differences in perennial ryegrass for nitrogen use efficiency in leaf growth following defoliation: performance in flowing solution culture and its relationship to yield under simulated grazing in the field

Varietal differences in rates of NO3 uptake and remobilization of nitrogen (N) during a cycle of severe defoliation and regrowth were assessed in perennial ryegrass (Lolium perenne L.) varieties Ba11778, Aberelan, Talbot and Gator. Plants were grown in flowing solution culture for 34 days, prior to a 30 d treatment period, including 21 d of regrowth. Net uptake of NO3 was measured continuously from solutions maintained automatically at 10 mmol m-3NO3.15 N-labelled NO33 was supplied to the plants in situ for either 21 h immediately prior to defoliation, or for 7-11 days afterwards, to measure remobilization of N from roots and stubble into the regrowing leaves. The four varieties differed only slightly in total dry matter production over 30 d, but varied substantially in post-defoliation specific growth rate by the leaf fraction. Gator was the lowest ( 0.11 g g-1 d-1), Ba11778 the highest ( 0.15 g g-1 d-1) and Aberelan and Talbot intermediate in leaf regrowth rate. Varieties did not vary significantly in shoot: root dry weight ratio, but the rate of NO3 uptake per unit of leaf fresh weight during regrowth was 27% lower in Ba11778 than in Gator. Leaves of Ba11778 and Aberelan had a lower organic N concentration in the dry matter at the end of the regrowth period than Talbot, which, in turn, had a lower concentration than Gator. Varieties differed in amount of leaf dry matter produced per unit of N absorbed by the plants after defoliation, the values (g g-1 N) being Ba11778 (22.6 ), Aberelan (20.7), Talbot (18.3) and Gator (16.7). More N was remobilized from the roots than from the stubble after defoliation. There were no significant differences among varieties in the amount and rate of N remobilization following defoliation. In earlier field experiments employing frequent cutting to simulate grazing, Ba11778 and Aberelan yielded at least 10% more dry matter annually than Talbot which, in turn, outyielded the amenity variety Gator by a similar amount. Thus the present results are consistent with the hypothesis that the efficiency of N use in leaf growth is an important factor determining genetic variation in productivity under frequent defoliation in the field when the herbage produced consists primarily of leaf.

Characterization of novel inbred lines of white clover (Trifolium repens L.). II. Variation in N2 fixation, NO3- uptake and their interactions

AbstractN2 fixation, nitrate uptake, and tissue N levels werecompared in four novel self-fertile inbred lines (referred to as A, B, C andD) of white clover (Trifolium repens L.) believed to differ markedly intheir nitrogen relations. Plants were inoculated with a mixture of Rhizobiumstrains and grown in flowing nutrient solutions without mineral N for 18 dprior to supplying half the plants with 20 µM

A Genetic Association Between Leaf Elongation Rate and Flowering Time in Perennial Ryegrass

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Effects of N deprivation and nitrate pulses on NRT1 and NRT2 transcript levels and nitrate influx rate in Brassica napus L.

over a 36 d treatment period. Net uptakeof

Nitrogen storage and remobilization in Brassica napus L. during the growth cycle: effects of methyl jasmonate on nitrate uptake, senescence, growth, and VSP accumulation

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