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Item Animal behaviour and dietary preference of dairy cows grazing binary and diverse pastures under the leaf regrowth stage defoliation criterion(Elsevier B.V., 2024-11-05) Oliveira BA; López FF; Cranston LM; Poli CHEC; Kemp PD; Donaghy DJ; Draganova I; López-Villalobos NIn New Zealand, intensively managed pasture-based dairy systems rely on binary pastures mostly comprised of Lolium perenne L. and Trifolium repens L. More frequent and extreme climatic events have been negatively affecting the persistency and production of these pastures, which now present increased seasonality, with marked peaks and troughs of production throughout the year. Diversification of plant species offers a solution to deal with increased seasonality. However, little is known about animal behaviour and dietary preferences of dairy cows grazing diverse pastures. The present study aimed to assess the grazing preferences of dairy cows when unrestrictedly offered binary (L. perenne and T. repens; Bi) and diverse pastures (L. perenne, Bromus valdivianus Phil., Dactylis glomerata L. and T. repens; Mix) subjected to three different leaf regrowth stage (LS) defoliation criteria. Secondarily, the study aimed to determine the main plant-related drivers for any potential animal preference. The treatments were MixLp (defoliated at L. perenne LS), BiLp (defoliated every time MixLp was defoliated), MixBv (defoliated at B. valdivianus LS) and BiBv (defoliated every time MixBv was defoliated), MixDg (defoliated at D. glomerata LS) and BiDg (defoliated every time MixDg was defoliated). Dairy cattle were evaluated over five agricultural seasons. The response variables were grazing time and location, bite rate, animal behavioural activity, pre-grazing herbage mass, undisturbed sward height, lamina:stem ratio, crude protein, metabolisable energy, organic matter digestibility, non-structural carbohydrates, neutral detergent fibre and lignin. Where significant differences were found, binary pastures presented lower sward height and higher non-structural carbohydrate content in comparison to the diverse pastures under the same LS defoliation criteria. However, no significant differences were found in the percentage of time that cows spent grazing both pastures. Season was the greatest contributor to the proportion variation found in all response variables, with values ranging from 47.55 % up to 88.77 %. In winter and spring, cows modulated their grazing behaviour (proportional time spent grazing, ruminating, or idling), investing more time actively grazing pastures under L. perenne LS interval of defoliation (2.5–3.0 LS), the criterion which resulted in shorter grazing rotations. This study allowed us to understand the suitability of diverse pastures from an animal perspective, and highlighted that independent of the pasture type, the positive productive and nutritional effects of defoliation management based on the LS may also extend themselves to positive outcomes in animal preference, interpreted as the percentage of time dairy cows spend grazing rather than ruminating or idling across and within seasons.Item An investigation of pasture legume root and shoot properties that influence their rate of decomposition in soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2021) Walker, HelenAgriculture is the largest source of GHG emissions (47.8 %) in New Zealand. Emissions are increasing annually, driven by increasing relative productivity. Irrespective of the climate regime, grassland soils have historically sequestered large amounts of atmospheric C into SOM (soil C) raising interest in the potential for agricultural emissions to be mitigated through acceleration of soil C sequestration. Soil C sequestration is a direct result of the rate of deposition (excreta, plant litter, and roots) exceeding the rate of decomposition and can be raised by: 1) increasing the rate of input (manipulating the drivers of vegetation); or 2) increasing the longevity of C in the system. This PhD study tests the hypothesis that C sequestration in pasture soils can be accelerated, by selecting pasture species that contribute slower decomposing litter to soil. A series of laboratory incubation studies were conducted to measure the decomposition rate (CO₂ emissions) of plant shoots and roots with high (Lotus pedunculatus) and low (Trifolium repens) tannin contents. In addition the effects of residue management (fresh and freeze dried), application to soil (fresh - surface, freeze dried - surface, and freeze dried - mixed) and rate of application (2, 5, 10 mg C. g⁻¹ soil) were evaluated. The effect of species, plant management, plant part, and rate of application on C emissions were all statistically significant (P < 0.05), with large variance in CO₂ emissions associated with all treatments. Plant species and plant part influenced the amount of C retained in the soil, although not entirely as expected. Lotus pedunculatus shoot material retained significantly more C than Trifolium repens shoot material at all rates of application (2, 5, 10 mg C. g⁻¹ soil); whereas Trifolium repens root material retained significantly more C than Lotus pedunculatus root material at all rates of application (P < 0.05). Notably plant roots and particularly Trifolium repens roots had slow decomposition rates compared to shoot materials. Research showed that soil and plant residue preparation greatly influenced the total amount of C retained for both shoot and root treatments, with more C retained under conventional incubation techniques (dried - mixed application) than with fresh applications. This indicates that CO₂-C retention in a field situation may be overestimated if predicted using conventional laboratory incubation techniques. However from a research perspective it is infinitely easier to work with pre-dried incubation materials (timing, handling, chemical analysis) so it is highly likely that this style of incubation practice will continue to be the preferred method of research. Care must therefore be taken when extrapolating the results from such incubation studies. A four compartment (2 soil C pools, persistent and labile; and 2 plant C residue pools, fast and slow) computer simulation model was developed and provided an excellent explanation of the CO₂ emissions from the incubation of fresh shoot and root material. The measurement of the metabolisable energy (ME) or lignin contents of plant shoot and root were successful in parameterising (allocating C to) the fast and slow plant residue pools. Plant tannin content was not able to explain CO₂ emission rates. The experimental and modelling studies provide evidence that grazed pasture rotations in mixed farming systems could be manipulated, by careful plant pasture species selection, to accelerate soil C sequestration. Litter and root metabolisable energy (ME) or lignin contents could be useful in species selection, but further research into other pasture species and pasture management techniques is required. Field studies should focus on the role of clover (Trifolium repens) roots in building pasture soil C content.Item Detection of loci associated with water-soluble carbohydrate accumulation and environmental adaptation in white clover (Trifolium repens L.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand(Massey University, 2021) Pearson, SofieWhite clover (Trifolium repens L.) is an economically important forage legume in New Zealand/Aotearoa (NZ). It provides quality forage and a source of bioavailable nitrogen fixed through symbiosis with soil Rhizobium bacteria. This thesis investigated the genetic basis of two traits of significant agronomic interest in white clover. These were foliar water-soluble carbohydrate (WSC) accumulation and soil moisture deficit (SMD) tolerance. Previously generated divergent WSC lines of white clover were characterised for foliar WSC and leaf size. Significant (p < 0.05) divergence in foliar WSC content was observed between five breeding pools. Little correlation was observed between WSC and leaf size, indicating that breeding for increased WSC content could be achieved in large and small leaf size classes of white clover in as few as 2 – 3 generations. Genotyping by sequencing (GBS) data were obtained for 1,113 white clover individuals (approximately 47 individuals from each of 24 populations). Population structure was assessed using discriminant analysis of principal components (DAPC) and individuals were assigned to 11 genetic clusters. Divergent selection created a structure that differentiated high and low WSC populations. Outlier detection methodologies using PCAdapt, BayeScan and KGD-FST applied to the GBS data identified 33 SNPs in diverse gene families that discriminated high and low WSC populations. One SNP associated with the starch biosynthesis gene, glgC was identified in a genome-wide association study (GWAS) of 605 white clover individuals. Transcriptome and proteome analyses also provided evidence to suggest that high WSC levels in different breeding pools were achieved through sorting of allelic variants of carbohydrate metabolism pathway genes. Transcriptome and proteome analyses suggested 14 gene models from seven carbohydrate gene families (glgC, WAXY, glgA, glgB, BAM, AMY and ISA3) had responded to artificial selection. Patterns of SNP variation in the AMY, glgC and WAXY gene families separated low and high WSC individuals. Allelic variants in these gene families represent potential targets for assisted breeding of high WSC levels. Overall, multiple lines of evidence corroborate the importance of glgC for increasing foliar WSC accumulation in white clover. Soil moisture deficit (SMD) tolerance was investigated in naturalised populations of white clover collected from 17 sites representing contrasting SMD across the South Island/Te Waipounamu of NZ. Weak genetic differentiation of populations was detected in analyses of GBS data, with three genetic clusters identified by ADMIXTURE. Outlier detection and environmental association analyses identified 64 SNPs significantly (p < 0.05) associated with environmental variation. Mapping of these SNPs to the white clover reference genome, together with gene ontology analyses, suggested some SNPs were associated with genes involved in carbohydrate metabolism and root morphology. A common set of allelic variants in a subset of the populations from high SMD environments may also identify targets for selective breeding, but this variation needs further investigation.Item Impact of phosphate fertiliser derived fluorine on soil microbiology and white clover (Trifolium repens L) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Environmental Sciences at Massey University, Palmerston North, New Zealand(Massey University, 2019) Thangavelautham, GeretharanFluorine (F) is a significant contaminant in most phosphate fertilisers and fertiliser-derived F is accumulating in New Zealand agricultural soils as a consequent of phosphate fertiliser application. There is potential for soil fluoride (F⁻) to detrimentally affect soil biological functions such as nitrogen fixation by Rhizobium leguminosarum, and to alter soil properties. Fluorine accumulation in soil may require changes to future land use and management practices. The aim of this thesis is to investigate whether phosphate fertiliser-derived soil F has a detrimental effect on soil microorganisms. A novel analytical method for soil F analysis was developed to measure the total soil F concentration based on extraction with dilute NaOH. The relative error between a novel 4 mol L⁻¹ NaOH extraction and the conventional fusion method was < 2 for organic-matter and volcanic parent material derived soils but was > 2 for recent and pallic soils. Precision of the 4 mol L⁻¹ NaOH extraction method, measured through repeat analysis of three further soils (n = 270), was calculated as < 9% Relative Standard Deviation (RSD). To define a standard method to quantify the bioavailable F concentration in soil, samples were extracted with water, 1 mol L⁻¹ HCl, 0.01 mol L⁻¹ CaCl2, 0.01 mol L⁻¹ KCl, and 1 mol L⁻¹ NH4Cl. Compared to water, 0.01 mol L⁻¹ CaCl2 had high relative recovery (of bioavailable F) in soils which have elevated Fe and Al content. Therefore, 0.01 mol L⁻¹ CaCl2 is recommended to measure the bioavailable F concentration of New Zealand pastoral soils. There is no data available which describes the toxic effect of bioavailable F on R. leguminosarum in New Zealand soils. A laboratory incubation experiment and MicroResp 96-well format respiration-inhibition assay were conducted to investigate the effect of F on R. leguminosarum and white clover. Rhizobium leguminosarum growth was not significantly suppressed by F⁻ concentrations less than 100 mg L⁻¹. The normal rod-shaped bacterium cell of R. leguminosarum was morphologically altered when exposed to F⁻ concentrations above 100 mg L⁻¹. The IC10 values determined for F⁻ toxicity to R. leguminosarum were higher than 100 mg F⁻ L⁻¹. Pottle-based experiments showed that white clover growth was not significantly supressed at a F⁻ concentration < 70 mg L⁻¹, while healthy nodules were formed up to a F⁻ concentration of 100 mg L⁻¹. Light and TEM micrographs of nodules revealed that the Rhizobium-white clover interaction was not influenced by F⁻ concentrations up to 100 mg L⁻¹. To assess the potential effects of lime and compost amendment on the bioavailability of F, laboratory F⁻ adsorption/desorption experiments were conducted. Results revealed that at pH < 6, F⁻ adsorption significantly (p < 0.05) increased as a function of compost application. At soil pH > 6, F⁻ adsorption was not significantly (p > 0.05) influenced by compost. Lime application increased the soil pH and maximum F⁻ adsorption was recorded at soil pH between 5.5 – 6.8. These results showed that soil pH significantly influences (p < 0.05) F⁻ desorption and this should be considered in the management of pastoral soil with elevated F. A pot trial was conducted to quantify the effect of added F (equivalent to 0 - 50 years of F accumulation via the continuous application of phosphate fertiliser) on soil properties, soil microbial activity, white clover growth, and R. leguminosarum in an Allophanic soil. F addition (0 – 385 mg kg⁻¹) significantly (p < 0.05) increased soil pH and Dissolved Organic Carbon (DOC) from 5.18 to 5.53 and from 270.5 to 331.3 mg kg⁻¹, respectively. The CaCl2-extractable F concentration increased from 4.95 to 12.67 units as a function of added F. Microbial biomass carbon and soil enzyme activities, and white clover growth and interaction with R. leguminosarum, were not influenced by added F⁻ up to the highest concentration used in this study. White clover variety Merlyn and Tribute shoot F concentration was increased from 4.9 to 19.9 mg kg⁻¹ DM and 5.12 to 16.68 mg kg⁻¹ DM, respectively, however these concentrations are not expected to represent a risk to grazing livestock. This study highlights that the 4 mol L⁻¹ NaOH extraction method is a simple and accurate technique to measure the total F concentration for soils which have high Fe, Al and organic matter content. Water extractable and 0.01 mol L⁻¹ CaCl2-extractable F concentration are recommended to measure the bioavailable concentration of F in New Zealand soils. Current New Zealand bioavailable F concentrations are orders of magnitude lower than the F⁻ concentration assessed to be toxic to R. leguminosarum and white clover, and this suggests there is no imminent risk of soil F to R. leguminosarum. Compost is not recommended as an amendment for soils which have a pH above 6.0 to minimize the bioavailable soil F⁻ concentration. Lime application is suitable in such soils to minimize the bioavailable soil F⁻ concentration through altering soil pH. The major fraction of added F is immobilised by Allophanic soil and this effectively reduces the available F concentration to plants and soil microorganisms. Future work is recommended to investigate the uptake mechanism of bioavailable F into white clover shoots and roots. However, there is no evidence to suggest that F concentrations in New Zealand soil are a risk to New Zealand’s pasture-based farming systems.Item Assessing the potential of genomic selection to improve yield and persistence in white clover : a thesis presented in the partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Plant Biology at Massey University, Manawatu, New Zealand(Massey University, 2020) Ehoche, Oiwodu GraceWhite clover (Trifolium repens L.) is an economically important forage legume in temperate pastures, providing quality fodder and plant-available nitrogen. However, its potential has not been fully exploited due to unpredictable herbage yield and poor vegetative persistence in pasture. Identification of genotypes that combine traits essential for yield and vegetative persistence, like dry matter yield and stolon density, are key objectives in breeding programmes. Long breeding cycles, high genome complexity and difficult-to-phenotype traits, usually assessed at late growth stages, are major constraints to conventional phenotypic selection in white clover breeding. In cultivar development programmes, elite individuals must be accurately identified and selected before crossing to generate superior progeny. Genomic selection is becoming a preferred method for increasing the rate of genetic gain by enabling early identification and selection of superior individuals, based on their genomic estimated breeding values (GEBVs), which can be generated without the need for phenotyping. Genomic selection is usually performed using a statistical model developed using genotypic and phenotypic information derived from a training population. In forage breeding, as parental breeding values are estimated by progeny testing, phenotypic data used in genomic prediction models is obtained from half-sib progeny. Recent single nucleotide polymorphism (SNP) genotyping methods like genotyping by sequencing (GBS) which generate a large volume of SNP marker information at low cost, have made genomic selection possible for species such as white clover. The main objective of this thesis was to explore the potential of genomic selection to improve important traits in white clover breeding. Our results indicate, for the first time, an integrated phenotypic and genomic selection approach to be superior to conventional phenotypic selection at increasing genetic gain for a simple trait in white clover. This demonstrates the potential of genomic selection to be used in enhancing white clover breeding programmes for quantitative trait improvement.--Shortened abstractItem Glyphosate displacement from New Zealand soils and its effect on non-target organisms : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science at Massey University, Palmerston North, New Zealand(Massey University, 2019) Jimenez Torres, Jesus AdalbertoGlyphosate (GlyP) is the most commonly used herbicide worldwide; it is retained in the soil and is decomposed by soil microorganisms. The main degradation product of GlyP is Aminomethyl-phosphonic acid (AMPA). Phosphorus and GlyP are antagonistic anions that compete for the soil’s reaction sites; P accumulation in the soil can increase GlyP translocation through the environment and increase its bioavailability. Residual GlyP and AMPA accumulation in the soil has generated concerns about their potential toxicity to non-target organisms such as crops and soil microorganisms. GlyP in situ remediation has therefore emerged as an option to reduce the residence time of the herbicide in soil. Laboratory experiments were carried out in order to elucidate the effect of the interaction between soil chemical and physical properties, and phosphorus addition on GlyP sorption to soil surfaces. The results of the GlyP-AMPA batch adsorption- desorption experiment demostrated that the Kd and fixation of GlyP and AMPA in the soil was proportional to the Al-Fe oxy-hydroxides content of the soil, in the following order Allophanic>Brown>Pallic. In another experiment, phosphorus addition to soil reduced GlyP adsorption, which demonstrated that phosphate will occupy the same soil reaction sites as GlyP. These results suggest that due to the stability of the bond formed between Al oxy-hydroxides and P, Al oxy-hydroxides will fix GlyP; while the higher reactivity of Fe oxy-hydroxides will facilitate the exchange of phosphate by GlyP. A column leaching experiment demonstrated that the interaction between the physical and chemical characteristics of the soil will influence water infiltration and solubilisation of GlyP. Phosphorus addition to the columns enhanced GlyP’s vertical displacement through the soil and AMPA detection in the leachate. The Pallic soil with a poor physical structure had reduced GlyP vertical displacement. In contrast, the free- drained Brown soil had higher AMPA percolation regardless of the P addition. The Allophanic soil had the lowest GlyP percolation risks, despite the fact that P addition increased AMPA detection at the bottom of the column. However, AMPA was undetected in the Allophanic soil’s leachate. A soil induced respiration (SIR) experiment demonstrated that GlyP (variable doses) did not affect soil microorganism respiration, while Agave amendments were used as an exogenous source of carbon and triggered soil respiration (Agave applied had 0.382 mg TC/g soil and control C applied was 1.25 mg C/g soil). The SIR ratio values observed in the soils were as follows Allophanic>Pallic>Brown, and were inversely proportional to the total dissolved carbon concentration in soil extracts. These results demonstrate that the greater Al- Fe oxy-hydroxide content of the Allophanic soil protected organic matter from mineralisation enabling greater microbial activity over the GlyP molecule. The P adsorption-desorption experiment using Agave powder demonstrated that Agave constituents desorbed phosphorus from soil surfaces, which might help in the desaturation of P from soil, while increasing its bioavailability. Glasshouse experiments using Roundup doses and Agave amendment applied to the soil of white clover potted plants were carried out in order to elucidate the potential for GlyP degradation in soil and the biochemical responses of white clover plants. The results demonstrated that Agave amendment attenuated the translocation of GlyP to white clover shoots for a Roundup dose of 90 kg a.i./ha. The chemical constituents of Agave, 12 hrs after GlyP application to the soil, enhanced GlyP degradation to AMPA in soil at the 15 kg GlyP treatment. A similar improved GlyP degradation was observed during three days of evaluation at the 7.5 kg dose. The biochemical responses of white clover shoots demonstrated an increase of gallic acid and tartaric acid accumulation proportional to the increasing Roundup doses. This suggested that Roundup alone, and in combination with Agave amendments, exerted oxidative stress on the plants. Alternatively, the herbicide could have affected the EPSPS enzyme disrupting the carbon cycle. These results demonstrate that the white clover metabolic disruption caused by the Roundup treatments of 7.5 and 15 kg/ha, expressed through tartaric acid and gallic acid, was alleviated at the third day of evaluation. The results of this thesis can support decision-making for the implementation of strategies which could mitigate glyphosate and AMPA displacement from New Zealand farmland; as example, it may encourage the prevention of phosphorus accumulation in the farmland. In addition, these results can encourage the development of further research related to the potential use of Agave amendments for glyphosate remediation, and help in the understanding of the effects of the herbicide on the metabolism of non-target organisms.Item The expression in soil bacteria of symbiotic genes from Rhizobium leguminosarum biovar trifolii : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University(Massey University, 1994) Fenton, MichaelRhizobium leguminosarum biovar trifolii strain ICMP2163::Tn5 was able to spontaneously transfer its pSym to the non-nodulating Rhizobium loti soil isolate NR40 in sterile soil microcosms containing Ramiha hill soil or Ashurst silt loam soil at pH 6.0 or higher. In sterile soil microcosms at pH 6.0 containing sterile ryegrass or white clover plants the frequency of NR40 transconjugants was higher than in microcosms containing soil alone. The survival of the parent strains decreased in soil with a pH of 5.5 or less, and no transconjugant NR40 bacteria were detectable. Southern blots of the genomic digests probed with nodA DNA confirmed that transconjugant NR40 contained symbiotic genes. On artificial media strain ICMP2163::Tn5 transferred its symbiotic plasmid, by conjugation, to Sphingobacterium multivorum, an organism that can be found in soil. The transconjugant bacteria were able to nodulate white clover seedlings but were unable to fix nitrogen. Microscopic examination revealed that the root nodule structure, and bacteroid formation, were abnormal. The bacteria occupying the nodules were isolated and the total DNA extracted. The partial 16S RNA gene sequence from a transconjugant derived from a nodule was shown to be identical with that of the recipient S. multivorum. Southern blots of the genomic digests probed with nodA DNA confirmed that the transconjugant contained symbiotic genes. A Caulobacter crescentus sewage isolate was also able to induce a tumour like growth on white clover seedlings after receiving the pPN1 co-integrate plasmid from E.coli strain PN200. Eckhardt gel analysis confirmed that the transconjugant Caulobacter carried the R68.45:pSym co-integrate plasmid. Bacteroids were absent but Caulobacter cells were found in the outer two or three layers of the growth and the plant cells in this region had degenerated. Sequence data was obtained for a 260 bp fragment of the 16S rRNA gene from Sphingobacterium multivorum and Caulobacter crescentus corresponding to postions 44 to 360 on the Escherichia coli genome. A distance matrix was constructed showing the relationship between S. multivorum, C. crescentus, Rhizobium, and related bacteria and neighbor-joining was used to construct a tree. From the tree given it is concluded that the ability to carry or express symbiotic genes is not dependant on having a phylogenetic relationship with Rhizobium.Item A preliminary investigation into the root systems of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) using a prescribed sampling method for the study(Massey University, 1939) Hopewell, H GThe roots of' plants are the least known, least understood and least appreciated part of the plant." Weaver end Bruner. The fundamental importance of an extensive, well developed and healthy root system cannot be over emphasised. It must hold the plant firmly in the ground, provide a large effective absorptive area through which ample nutrients will become available for growth, and, by penetrating deeply, or by building up reserves, it must protect plant against the exigencies of a dry season. The study of the roots then, important as they are, would appear to have been unduly neglected when one considers the amount of research carried out using as a basis some above ground feature of the plant. In this connection W.F. Loehwing ( 1) may be quoted - "As one surveys the monumental literature dealing with crop production, the small fraction thereof devoted to roots and the absorption processes seems entirely out of prorortion to their importance. [From Introduction]Item Aspects of the regulation of inflorescence initiation in white clover (Trifolium repens L.) : a thesis ... for the degree of Master of Science in Botany at Massey University(Massey University, 1982) Havell, David CharlesThomas (1962), found that after a pretreatment of warm short days, one genotype of 'Grasslands Huia' white clover, clone C, flowered in long days. Another 'Grasslands Huia' genotype did not, (clone B). Experiments with clone C revealed the following: (a) Production of a translocatable floral stimulus occurred in long days and continuous light. (b) Production of either translocatable inhibitory or promotive factors did not occur in short days. Although flowering was caused by long days, flowering eventually stopped. Experiments designed to test the hypothesis that this was caused by the build up of translocatable inhibitors were inconclusive. There was no evidence in the same experiments that translocatable products produced in short days stopped the cessation of flowering. The effect of the short day light intensity on flowering in long days was also examined. Results indicated that in long day conditions when the photoperiod was near the critical daylength, the light intensity of the short day pretreatment limited flowering. At higher daylengths and in higher long day light intensities, the short day light intensity had no influence on flowering. This supports the idea of Thomas (1981), that a balance between two factors, one inhibitory one promotive controls flowering. Further support for this concept came from studies with clone B in which it was found that a cool pretreatment would enable clone B to flower in continuous light but not in 16h photoperiods. Other experiments with clone B, showed that it produced a translocatable floral stimulus in continuous light. There was no evidence that clone B produced translocatable inhibitors in vegetative conditions although there were indication that warm conditions could inhibit the response of the apex to the floral stimulus. Grafts of clone C on clone C, clone B on clone C, Kalinin A on clone C, were used to test the hypothesis that apical factors limited apical responses to the floral stimulus. Given that clone B had the weakest response to the floral stimulus from clone c, and Kalinin A had a stronger response than clone C it would seem that the hypothesis is correct. Grafts were also used to test the hypotheses that (a) Clone B produced translocatable inhibitors which blocked flowering. (b) Clone B produced a translocatable floral stimulus which it was inhibited from responding to. Neither hypothesis was supported by the results. In conclusion it appeared that a balance between two factors controlled the amount of the floral stimulus translocated from the leaves. It also seemed likely that a interaction between the floral stimulus and the apex had a regulatory role. Differences between white clover genotypes are probably due to differences in apical and leaf processes. The limitations of the experimental methods and futive experiments were also discussed.Item Some aspects of leaf death during the regrowth of a perennial ryegrass (Lolium perenne L.) white clover (Trifolium repens L.) sward : a thesis presented in partial fulfilment of the requirements for the degree Master of Agricultural Science at Massey University(Massey University, 1968) Hunt, Warren FergusonIn order to achieve high animal production from grass-legume pastures such as are used in New Zealand, it is necessary to meet three basic requirements. (a) large amounts of high quality feed must be grown, the seasonal distribution of which must approximate the seasonal curve of animal requirements. (Conservation practices can be used to rectify minor discrepancies.) (b) A large proportion of this feed must be harvested by the animal. (c) Efficiency of conversion within the animal must be at a high level. (McMeekan 1956) Agronomists are concerned primarily with the first of these factors, but as maximum production for a system is approached, the second factor assumes major importance. These aspects must be studied against the background of a wide range of management techniques that may be employed in defoliating pastures. In the past, the importance of both leaf area grass tiller density and organic reserve materials have been studied as they are influenced by defoliation management, and their role has to some extent been determined. (Milthorpe and Davidson 1965). The emphasis in such investigations has been on the initial stages of regrowth from defoliation and there remains a number of aspects of primary productivity at medium and high Leaf Area Index values (L.A.I. i.e. the area of leaf per unit area of ground) requiring investigation (Brougham 1962, Alberda 1965a, Brown and Blaser 1968). One of these aspects, leaf death, is the subject of the investigation reported below and has been selected because of its significance to both productivity and utilisation. [From Introduction]