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    Effect of herb-clover mixes on weaned lamb growth : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palerston North, New Zealand
    (Massey University, 2014) Somasiri, Sharini Carol
    The quality and production of ryegrass (Lolium perenne L.) /white clover (Trifolium repens) pastures are seasonal in New Zealand. Earlier research showed that a sward mix of plantain (Plantago lanceolata), chicory (Cichorium intybus L.), white- and red-clover (Trifolium pratense) resulted in greater lamb live weight gains in the late summer early autumn period. However, this has not been tested across all the seasons in New Zealand. Therefore, research was undertaken for two consecutive years (2011/2012 and 2012/2013) on three sward mixes; Pasture mix, Plantain mix and Chicory mix in early spring, late spring and early summer (late spring), summer and autumn. The Pasture mix consisted of perennial ryegrass and white clover. The Plantain mix consisted of plantain, white- and red-clover. The Chicory mix consisted of plantain, chicory, white- and red-clover. It was hypothesised that lamb performance (live weight, live weight gain (LWG) and carcass weight) and apparent carcass weight production per ha would be greatest in the Plantain and Chicory mixes in all four periods. Secondly it was hypothesised that Plantain and Chicory mixes would have lower feed conversion ratios (FCR) with higher herbage utilization efficiencies (EHU%) than the Pasture mix. In each period weaned lambs were reared in the three herbage treatments for a maximum of two months. Lambs were weighed fortnightly and they were slaughtered within 12 hours of being off the pasture at the end of the experiment. Carcass weights were obtained from the abattoir. The Plantain and Chicory mixes had a higher feeding value than the Pasture mix during early spring to autumn. Both Plantain and Chicory mixes produced heavier (P<0.05) lambs, higher (P<0.05) live weight gains (LWG) and carcass weights compared to the Pasture mix in all periods. Total apparent carcass weight production per ha were 407, 748 and 709 kg/ha in year one and 474, 607 and 642 kg/ha in year two in the Pasture mix, Plantain mix and Chicory mix, respectively. Both Plantain and Chicory mixes had lower (P<0.05) feed conversion ratios (FCR) and higher (P<0.05) herbage utilization efficiencies (EHU%) compared to the Pasture mix. This research has shown that sheep farmers in New Zealand can finish lambs at a faster rate for heavier carcasses using herb-clover mixes from spring to autumn than on ryegrass/white clover pastures.
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    Effect of slope class on defoliation frequency and severity of Trifolium repens by sheep in hill pastures : a thesis presented in partial fulfilment of the requirements for the degree of Master in Applied Science at Massey University
    (Massey University, 1996) Liu, Cunqi
    Hill pastures demonstrate varying intensities of grazing related to slope. A study of this effect was carried out at the Ballantrae Hill Country Research Station on set-stocked pastures that were maintained on high (H) and low (L) soil fertilizer/stocking rate treatments. In the first experiment, 10 marked white clover stolons were observed at 1-week intervals for grazing damage in each (200 * 300 mm) of 10 paired quadrats on both flat terrain (FT) between 0-20° and steeply sloping terrain (ST) between 30-45° in each of two treatments (H & L) in winter of 1995. The defoliation frequency (0.38 vs 0.29 ± 0.10; P<0.05) and severity (0.45 vs 0.30 ± 0.11; P<0.05) were significantly higher on the FT than on ST, but this phenomenon only occurred on the H treatment. In order to determine the reason for causing sheep grazing discrimination between terrain, 10 sites that contained the FT and ST were selected on the L treatment. At each site, four paired turves (200 * 300 mm) were cut, two turves were from the FT and the other two from the ST, were transplanted into similar or contrary terrain to give all combinations of turf and terrain in spring of 1995 and again in autumn of 1996. In autumn, turf from the FT was grazed more frequently (0.38, 0.36 vs 0.15, 0.11 ± 0.18; P<0.001) and severely (0.81, 0.87 vs 0.28, 0.19 ± 0.41; P<0.001) irrespective of its location in the sward, but this effect was stronger within the first three weeks of the grazing period. In contrast, this phenomenon did not occur in spring, and when FT turf was transplanted into the FT it was less (0.09 vs 0.32, 0.31, 0.37 ± 0.23; P<0.05) severely defoliated than the other treatments. It is concluded that sheep generally defoliated white clover on the FT more frequently and severely than on the ST and the main reason for this discriminatory grazing was the difference in the vegetation conditions (e.g., botanical composition) of pastures. This preference for the FT was stronger during autumn, on the H treatment, and in the early stage of a grazing period. These findings suggest it may be possible to lessen discriminatory grazing in hill pastures by improving pasture botanical composition, adjusting fertilizer application rate or by seasonal manipulating of grazing polices.
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    Evaluation of the efficacy of the inducible over-expression of 9-cis-epoxycarotenoid dioxygenase1 (NCED1) to confer improved water use efficiency in transgenic plants : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Sixtus, Caleb D.
    In order to trial the concept of inducible overproduction of the plant hormone abscisic acid (ABA) to confer increased water use efficiency, the forage legume Trifolium repens (L.) (white clover) and the model plant species Nicotiana tabaccum (L.) (tobacco) were transformed with the construct 9-cis-epoxycarotenoid dioxgenase 1 (NCED1) gene from Solanum lycopersicon (SlNCED1) driven by the RUBISCO small subunit promoter (SSUp). For white clover, a total of 18 putatively genetically-independent transgenic lines were obtained through selection in tissue culture, and these were further cloned by vegetative propagation to give 56 plants in total. Ten of these tested positive for NCED1 insertion using polymerase chain reaction (PCR) with genomic DNA. Establishment of transgenic clover on soil was problematic, but seven putatively transformed lines were established. Of these, only one line potentially expressed SlNCED1, but the transcriptional levels were too low, as determined by semi-quantitative reverse-transcriptase dependent PCR (sqRT-PCR), for any further analysis. This low expression, and the fact that only one line was identified, led to the decision to discontinue investigations with white clover. In parallel, the more amenable tobacco transformation system was also used with the SlSSUp::NCED1 construct to act as proof-of-concept. Fourteen putatively genetically independent transgenic lines of tobacco were obtained through tissue culture, six of which were successfully established onto soil. A range of integrated gene copy numbers and NCED1 expression levels were identified in the To lines using genomic PCR and sqRT-PCR. Self-fertilised seed was collected from each transgenic line, but the germination rate from all of the transgenic lines was significantly lower than wild-type. Those lines that did germinate often displayed a range of aberrant growth phenotypes. After trialing methods to evaluate water use efficiency, a total of 47 T1 seedlings displaying a normal seedling phenotype were established on soil. A range of water use efficiencies were observed as determined by analysis of plant growth rates against water use, followed by a transpiration assay of plants deemed „efficient‟ and „poor‟ users of available water. No correlation of SlNCED1 expression with the more efficient users of available water was observed, and so ultimately it was concluded that the transgene was ineffective at raising the water use efficiency of tobacco as determined by the parameters measured in thesis.
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    Characterisation of nutrition responses in three genotypes of white clover (Trifolium repens L.) selected for tolerance to low phosphorus : a thesis presentation in partial fulfilment of the requirements for the degree of Master of Science in Plant Molecular Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Smith, Diantha
    This study focused on the differences in root system architecture (RSA) of three white clover (Trifolium repens L.) genotypes, designated 43-7, 45-14 and 47-9 that were isolated from breeding lines selected to tolerate low phosphorus (P). In this study, genetically identical white clover stolons were cut from stock plants at the fourth node, and primary roots emerged (post excision) from either of the two primordia at nodes three or four. The main objective was to establish if differences in RSA were observed in response to a limited P-supply (10 μM KH2PO4) compared with a sufficient P-supply (1 mM KH2PO4). Each of the cut stolons had a dominant primary root that was nominated to be used for the analysis of root growth in terms of elongation and lateral root emergence. The analysis was standardised by designating the branching zone as the region of the primary root that contained visible lateral roots. The remaining region was designated the elongation zone, and did not contain visible lateral roots. In P-sufficient media, the branching zone was approximately 50% of the primary root length by 15 days post excision and approximately 80% by 25 days in the three genotypes. After 30 days post excision, the branching zone was maintained between 85% and 90% of the primary root length. The response to low P was measured after the emergence of visible lateral roots in experiment I and prior to the emergence of visible lateral roots in experiment II. A third treatment group with a reduced sulfur supply (in experiment II) tested the specificity of the P-stress response. In summary, the morphological responses to P-stress were characteristic for each genotype; the changes to the primary and/or lateral roots occurred within seven days from the reduction in P-supply; and the timing of the reduction in P-supply influenced the degree of the response that was observed with respect to the branching zone. The responses to P-stress included a stimulation of the primary and lateral roots in 47-9 with a reduced root biomass under S-stress; a decrease in the number of visible lateral roots in 45-14; and the decreased elongation of lateral roots in 43-7, which reduced the initiation of tertiary roots. The branching zone decreased in 45-14 only when the P-supply was changed after lateral root emergence. In contrast, the branching zone increased in 47-9 only when the P-supply was changed before lateral root emergence. The results suggest that the P-stress response in the roots is specific and utilisation of P and S may differ in the three genotypes.
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    Analysis of seed production traits in interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Breeding and Genetics at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Naeem, Muhammad
    Trifolium repens L. (white clover) is an important component of New Zealand’s pastoral and herbage seed industries. It has delicate shallow roots vulnerable to drought and pest attack. T. uniflorum is a wild species, adapted to dry environments, with deep woody roots but poor vegetative growth and only 1-3 florets per head. Hybridization was done to incorporate the drought tolerance and root characteristics of T. uniflorum into white clover. The primary hybrids (F1 and BC1F1) showed poor seed production. The project aimed to analyse this problem and improve seed production by further hybridization and selection. The hybrids expressed high variation for almost all seed production traits. Heads per plant, florets per head and seeds per floret were important determinants with moderate to high heritabilities. The derived traits seeds per head, florets per plant and seeds per plant expressed low-moderate to moderate heritabilities. Flowering pattern showed high heritability. No negative correlations between seed production and root traits were found. Whereas nodes per stolon favoured head production, stolon production had a negative effect on nodes per stolon. No negative associations between head production, persistence and foliage production of the hybrids were observed. No cytoplasmic influences were evident. The hybrids showed, higher self fertility and a wider gap between potential and actual seed yield than white clover. The BC1F1 generation produced low numbers of heads per plant and seeds per floret. Intercrossing coupled with recurrent selection improved variation, fertility and realization of potential seed yield. The second backcrossed and intercrossed generations had high seeds per floret and plant. Backcrossing of selected hybrids effectively recovered the white clover phenotype and created new variation. The BC2F1 and BC3F1 generations expressed the better head production ability of T. uniflorum combined with the bigger head size of white clover. Seed production capability of the hybrids was successfully restored. More genetic variation was created in the hybrids for future breeding and selection endeavours.
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    Investigation of the possibility of introgression from Trifolium ambiguum M. Bieb. into T. repens L. : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Breeding and Genetics in the Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Ullah, Ihsan
    The objective of this project was to investigate the possibility of introgression of stress resistance traits from T. ambiguum (A) into T. repens (R) by interspecific hybridisation, using two approaches. The first used T. occidentale Coombe (O) as a genetic bridge because this species has chromosome pairing homology to both the two other species. The second approach attempted direct integration of genomes from the two species through ploidy manipulation. For the first approach, four crossing strategies used T. occidentale as a genetic bridge. Each started with different multispecies hybrids with various genomic contributions from the three parental species. The second approach began with 5x and 7x T. ambiguum x T. repens hybrids (ARRRR and AAARRRR). All the initial hybrids were repeatedly selfed, inter-crossed and backcrossed with colour-marked white clover and advanced progenies with reasonable levels of fertility were obtained in every strategy. Advanced hybrids were selected on the basis of flow cytometric ploidy estimation, phenotypes and somatic chromosome counts and were characterised for chromosome pairing and introgression events using both conventional and molecular cytogenetics. The advanced hybrid progenies were also grown in a sandpit to determine the relative expressions of the parental traits. Chromosome analyses showed evidence of chromosome elimination, chromosome addition/substitution, allosyndetic pairing involving A-derived chromosomes and interspecific genomic recombination. GISH analysis revealed that the genetic bridge strategy 1, which started with RRAO, gave a plant with four apparently large A-R and A-O chromosomal exchanges along with an A chromosome addition and a O-R substitution. No apparent signs of introgression were detected by GISH in the other strategies but introgression could not be ruled out because the sample was small and the morphology of the hybrids tested in the sandpit showed the expression of characters from both the parental species. These plants need to be characterised by using more genetic markers. The advanced progeny in the strategy based on direct integration of AxR genomes showed a low level of inter-specific chromosome pairing consistent with an absence of, or very low level of, introgression. The introgression revealed by GISH in the advanced progeny of RRAO hybrids provides evidence that using T. occidentale as genetic bridge has worked by disrupting the genomic integrity in T. repens. The material having introgression has many applications from white clover improvement point of view. While direct hybrids with A & R genomes did not lead to any apparent introgression.
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    The nutritional value of ryegrass-white clover leaf protein concentrate : a thesis presented in partial fulfillment [sic] of the requirements for the degree of Doctor Philosophy in Biochemistry at Massey University
    (Massey University, 1983) Johns, David Carville
    Leaf Protein Concentrate (LPC ) , which was manufactured from a mixture of Ryegrass and White Clover (Lolium perenne and Trifolium repens) at the Ruakura Agricultural Research Centre , was evaluated as a possible protein source for feeding to chickens . The nutritional value of LPC was compared to that of soybean meal ( SBM ) . LPC was shown to have a lower nutritional value than SBM in the growth trials . The addition of methionine or cystine to the diet containing LPC improved both food utilization and weight gain of the chickens . These growth parameters showed the greatest improvement when 2 g methionine/kg diet was added to the LPC diet. The additional quantity of 2g methionine/kg diet was similar to the amount of sulphur amino acid contributed by LPC to the d i e t ; 1.8 g sulphur amino acid from L PC /kg diet. When an equivalent amount of cystine (1.6g) to methionine , on a sulphur basis , was added to the LPC d i e t and fed to chickens , it was shown to support the same amount of growth and maintain a similar food utilisation level as additional methionine . LPC contributed only 0.6g cystine/kg of diet . As this was much lower than the added cystine and/or methionine , it was concluded that the availability of cystine in the whole diet was reduced by the presence of LPC rather than the lack of availability of cystine in LPC alone . The following information was also obtained : - (i) Pancreatic hypertrophy and increased pancreatic enzyme activity (trypsin and chymotrypsin ) occurred due to feeding the LPC diet . (ii) The invitro exhaustive enzyme digestibility study indicated that while the overall digestibility of LPC was approximately 6% lower than that of SBM, none of the individual amino acid digestibility estimates i n LPC diverged markedly from the mean . All LPC amino ac ids were released equally by enzyme hydrolysis . (iii) In contrast to the invitro findings , the in vivo mean amino acid availability estimates for the ingredient LPC (as measured in the excreta) were lower than the corresponding SBM estimates by approximately 1 5% . The cystine availability estimate for the ingredient LPC was only 5 1 . 2% in terms of corrected amino acid availability ( CAAA), and 1 1 . 9% in terms of apparent amino acid availability ( ApAAA). By comparison the cystine availability estimates for the ingredient SBM were 80 . 8% CAAA and 7 5 . 7 % ApAAA. When the diets containing LPC or SBM were assayed by the same technique , the differences in the amino acid availability estimates were markedly reduced . The availability estimates of cystine in the LPC diet were still lower than the other amino acid availability estimates for the LPC diet . These however were only 8-10% lower than the corresponding estimates for the SBM diet. (iv) The mean amino acid digestibility estimates, derived by analysis of the ileal contents of chickens fed with the LPC d i e t were 26% lower than those for chickens fed the SBM d i e t s . The cystine digestibility estimates for the LPC d i e t was approximately 45% lower than the corresponding cystine digestibility estimate for the SBM diet. These results indicated that digestion and/or absorption of the LPC diet was probably being retarded as compared with the SBM diet. (v) Supplementation of the LPC diet with the antibiotic , Neomix , gave an improvement in growth and an increase in the mean amino acid availability ( measured by excreta analysis ) of approximately 7%. This indicated that the gut microflora were influencing the nutritional value of LPC . Feeding the LPC diet in comparison to feeding the SBM diet also tended to increase the level of c1 9 cyclopropane fatty acid in the excreta. This indicated that feeding the LPC diet was influencing the nature and/or activity of the microfloral population . The physiological and metabolic effects of feeding r aw soybean meal and/or trypsin inhibitors , which have been reported in the literature, included pancreatic hypertrophy , increased pancreatic proteolytic enzyme activity , retardation of ileal protein digestibility and.an influence by gut microflora . Each of these factors were characteristic of chickens fed the 1PC diet. It was therefore concluded that the additional need for cystine or methionine by chickens fed the 1PC diet , was due to the presence of trypsin inhibitors in the 1PC . It was demonstrated, by feeding 1 - (methyl 14c) methionine that phenolic compounds were being methylated . However the need for detoxification of aromatic compounds , which required methionine (as a methyl donor ) and /or arginine ( ornithine ) , could not explain the growth depression experienced by chickens fed the unsupplemented 1PC diet. The feeding of 1- (methyl 14c) methionine in conjunction with the 1PC diet also indicated that the digestibility of methionine was not being hindered during the digestive process by preferential binding with other compounds in the 1PC diet. I t was concluded from the result s of this study that 1PC adequately supplemented with methionine , could b e a useful addition to the range of ingredients available for use in poultry feeds.
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    The influence of phosphorus supply on below ground interferences between browntop and white clover : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1993) Pannell, Claire Astley
    A low occurrence of white clover in pastures contributes to soil nitrogen (N) deficiency and a low quality feed for stock. There is evidence to suggest that competition for soil phosphorus (P) from roots of browntop plays an important role in determining the distribution of white clover in hill country swards. However, competition for soil P between roots of browntop and white clover has not been studied separately from other factors known to affect the growth and persistence of white clover (e.g., soil moisture, grazing management, shoot interferences (shading and physical impedance), and non-competitive root interferences). In hill country pastures, P level (phosphorus fertilisers), and defoliation (grazing management), are the main factors that can be changed by farmers to alter pasture botanical composition. The high cost of superphosphate has limited the potential of farmers to manipulate pastures using fertiliser applications. Therefore, it is important to know whether roots of browntop compete with roots of white clover for soil P, and whether a low supply of soil P will contribute to more severe competition from browntop roots. The possibility of non-competitive interferences occurring between roots of browntop and white clover must also be considered. How defoliation alters the balance of P acquisition between roots of browntop and white clover needs to be determined. Three techniques were employed to examine the nature of root interferences occurring between browntop and white clover: plant strategies; dual P isotope labelling; and a more traditional competitive settings trial using aerial partitions. Plant growth and root interferences were studied at a range of levels of soil P supply. Responses of growth and phosphorus uptake of browntop and white clover to increasing soil P supply were examined first, in the glasshouse, by growing monocultures of browntop and white clover in pots. Two mini-sward trials (one at deficient soil P supply, the other at adequate to luxury soil P supply) were carried out in the glasshouse to allow examination of root interactions (without shoot interactions). The basis of the experimental design was to determine the relative amounts of phosphorus-32 and -33 absorbed by a central row of plants (either browntop or white clover) from two adjacent soil spaces, one dominated by white clover roots, the other by browntop roots. 32P was injected into the soil on one side of the central row of plants, and 33P into the other side. 32p and 33p uptake was assessed by harvesting the shoots of the central plants, and counting the two isotopes. The competitive settings type trial compared the growth and P uptake of a single central plant in a small pot (no interference with other plants) with a central plant in a larger pot grown with roots associated with roots of plants of the same species (intraspecific association), or of the other species (interspecific association). Shoots of the central plant was separated from the shoots of outer plants by an aerial partition. The growth of browntop and white clover, and the nature of root interferences occurring within and between the two species was dependent on the level of soil P supply. However, the higher root density and specific root length (SRL) of browntop compared with white clover appeared to be the most important factor determining the success of browntop at all levels of soil P supply, regardless of whether or not browntop was grown with white clover. According to the plant strategy theory of Grime, browntop was found to be a stress tolerant plant. At low levels of P supply, the lower growth rate of browntop compared with white clover would be an important factor contributing to the dominance of browntop in hill country pastures. At adequate to luxury levels of soil P supply, shoot growth of browntop was more responsive than white clover, and browntop was capable of luxury consumption of P. The high growth rate and large demand for P contributed to the competitiveness of browntop at high P supply. However, the lower demand for P by white clover, and the high P supply may have enabled white clover to avoid competition with browntop. On unamended subsoil, browntop reduced P acquisition by white clover roots, and had a greater P uptake in the presence of roots of white clover than with roots of other browntop plants. Therefore, evidence of root competition for soil P from browntop with white clover was found. The competitive effect of browntop appeared to be due to browntop decreasing the availability of P in the soil, explained by browntop's ability to acquire more radioactive P from the soil than white clover. At low P supply (subsoil), P application, but not defoliation of browntop, reduced the competitiveness of browntop. At adequate P supply, the ability of browntop to acquire P was reduced by defoliation. The effect of defoliation was rapid (four days), and browntop was able to acquire P isotope to higher concentrations in the shoots than when undefoliated. Possibly the reduction of root competitiveness of browntop may be short-lived. Some interference, other than root competition, was occurring at intermediate to luxury levels of soil P supply, and may have masked the competitive effects of browntop. White clover appeared to benefit for P acquisition from growing with browntop, due to greater local root density compared with when growing with other white clover plants. Therefore, browntop and white clover appeared to gain mutual benefit for P acquisition from the presence of roots of the other species, and the competitive effects of browntop were not of overriding importance. The possibility of autotoxicity of white clover on its own root growth was discussed in relation to rhizosphere acidity effects on the toxicity of phenolics. At adequate to luxury levels of soil P supply, neither undefoliated browntop nor undefoliated white clover benefited from defoliation of adjacently growing white clover plants. However, at lower P supply, defoliation of white clover led to an increased P isotope acquisition by nearby browntop plants. Therefore, defoliation reduced the demand for soil P by white clover. Roots of browntop were not as tolerant of defoliation as white clover. In the field, the mat forming behaviour of browntop, physically impeding the growth of white clover and shading white clover stolons, would reduce the severity of competition for soil P between roots of browntop and white clover. Overall, root competition for P from browntop with white clover was found not to be as important as previously thought. The use of several experimental techniques allowed a clearer picture of the interferences that occur between browntop and white clover to be obtained. The nature of root interference changed with increasing P supply. The responses of browntop and white clover to increasing P supply was found to be enlightening when the plant strategy theory of Grime was used to compare browntop and white clover. However, the dual P isotope technique found plant interferences that were not detected by the other methods used (P response and competitive settings trial), and allowed interferences that were occurring simultaneously to be elucidated.
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    Influence of light on inflorescence development and seed yield in white clover (Trifolium repens L.) : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1990) Pasumarty, Satyanarayana Venkata
    White clover (Trifolium repens L.) florets have the capacity to produce up to 6 seeds, yet normally the average number of seeds per floret is somewhere between 2 and 3.5. The cause of this low seed set is not known, but such an understanding is necessary as a basis for the development of improved management practices for seed production. Low light intensity has been implicated in the reduction of seed number per flower head and even in the abortion of developing flower heads. Therefore the present study examined the influence of light intensity on inflorescence development and seed yield of "Grasslands Huia" and "Grasslands Pitau" white clover (Trifolium repens L.). Investigations were also carried out to examine the effects of light intensity on sink strength of young flower heads with a view to understanding the mode of action of light. Under controlled environmental conditions when plants were grown at a range of light intensities from 2000 to 10000 lux, the ovary length, number of florets per inflorescence, the size of the ovules within the carpel, percentage of fertile ovules and percentage of ovules setting seed in the plants grown at the lowest intensity were decreased by 18, 53, 13, 75% respectively compared with controls grown at the highest intensity. A stain-clearing technique was used to examine the cytoplasmic state of embryo sacs in intact, unfertilized, mature ovules. Ovules with fully formed embryo sacs containing a full complement of nuclei were classed as fertile ovule. Ovules with shrunken embryo sacs which lacked a full complement of nuclei were classed as sterile. Light intensity had no significant effect on ovule number. However, in the field, the young flower heads experience very low light levels due to shading by foliage canopy only when they are young. Within the canopy light intensities may be as low as 1% of full light even at midday when incoming radiation is most intense. To simulate field conditions in the glasshouse the inflorescences were shaded on otherwise fully lit plants by using either neutral shade or simulated shade light at wavelengths similar to those of light filtered through a leaf canopy. Low light had a slight effect on pollen fertility, the effect being significant only at some stages of inflorescence development. These stages of inflorescence development were synchronized with the development of pollen mother cells into pollen grain. Irrespective of the stage of inflorescence development, shading the inflorescence alone decreased the length of the ovary. The most striking observation was that even in good growing conditions only 70% of ovules formed in a flower head had fertile embryo sacs capable of setting seeds. The reduction in seed number per head was brought about by an increase in the number of florets aborting, and by a decrease in the percentage of ovules setting seeds. The close correlation between the percentage of apparently fertile ovules and the percentage of ovules setting seeds strongly suggests that this reduction was largely brought about by an increase in ovule sterility. The degree of ovule sterility was greatest when shade was applied to the inflorescence at the eighth node below the apex on a stolon. Shade treatments might have interfered with meiosis (formation of megaspores). To examine the significance of these observations for seed production practices, field experiments were set up to determine to what extent and under what growing conditions flower head development and seed yield per head were influenced by canopy density and simulated overcast weather conditions in plants of "Grasslands Huia" and also "Grasslands Pitau". Field studies showed that flower heads developed in a dense canopy produced 37-39% fewer seeds per head than those formed in an open canopy. Some of this reduction was brought about by an increase in the number of florets aborting, but much of it was caused by a higher proportion of sterile ovules in dense canopies than in open canopies. Simulation of overcast weather by artificial shading also strongly affected the seed yield per flower head. When plants were shaded before pollination only, there was a 24-31% reduction in seed number per head; when shade was applied only after pollination there was a reduction of 25-28%. Therefore overcast weather conditions during early stages of inflorescence development or during the seed maturation period could lead to reduction in seed number per head. In the past, low seed number per flower head has been attributed to poor pollination. The results obtained in the present investigation showed that a high percentage of pollinated carpels contained sufficient pollen tubes for the fertilization of all ovules. The observation of a random seed set pattern and a positive correlation between the ovule fertility and the ovules setting seed also strongly suggest that pollination was probably not the limiting factor. Rather, the limiting factor appeared to be the degree of sterility of unfertilized ovules. These results showed that there was a direct effect of light intensity on flower head development. Therefore investigations were carried out to study the influence of shade on the growth and sink activity of young flower heads and peduncles. Measurement of the peduncle elongation rate by using a linear voltage displacement transducer showed that when the inflorescence alone was shaded, peduncle elongation was higher than in the light. Translocation studies using a 11C-labelling technique showed that shading the inflorescence alone had little effect on translocation of assimilates into the inflorescence, but induced a major change in partitioning of assimilates within it. Peduncle elongation induced by shade was accompanied by an increase in partitioning of photoassimilates to the peduncle, at the expense of the flower head. The results of this study suggest that one of the major advantages of the practice of defoliation at the time of closing the paddock for seed production is probably the enhancement of ovule fertility; and that decreased seed yield in duller, wetter summers is probably, at least in part, attributable to increased ovule sterility in the dense canopies formed under those conditions. Form this point of view, for best seed production an optimal management strategy would be to grow the crop as spaced plants with an open canopy rather than a denser sward with a closed canopy.
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    Autecology of white clover (Trifolium repens L.) with special reference to the effect of stolon burial on branch formation : a thesis in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1994) Hay, M J M
    In moist temperate regions the persistence and productivity of white clover (Trifolium repens L.) in grazed pastures is dependent upon stolon growth, particularly stolon branching. However measurements of white clover in New Zealand pastures indicate that by the beginning of the growing season, generally 80% of stolon material is buried. The objective of this study was to investigate the effect of stolon burial on the branching of stolons and to utilize the findings to further the understanding of the autecology of white clover in grazed pastures. Distinct seasonal patterns of maximal stolon burial in spring and minimal branching of stolons in spring (both on a population and plant basis) were measured in a field trial established for the monitoring of the autecology of white clover under sheep grazing. Measurements of individual axillary buds on stolons artificially buried, under a range of conditions in the field, consistently found that the major effect of burial was to reduce branching by increasing (up to threefold) the probability of mortality of axillary buds following initiation of outgrowth. Initiation of outgrowth of axillary buds on stolon tissue that had emerged from the stolon apex while on the soil surface before being buried was not, except perhaps for those buds at the two youngest nodes at the time of burial, influenced by burial. Glasshouse experiments were performed in order to increase knowledge of factors controlling the initiation of outgrowth of axillary buds and to examine how stolon burial influenced outgrowth of axillary buds. Experiments involved measurements of the branching response of individual axillary buds on stolons subjected to differing burial/cultural treatments so that treatment responses could be separated from ontogenetic influences. Initiation of outgrowth of axillary buds was only severely lowered by burial when the node associated with a bud emerged from the stolon apex in soil and then remained in soil. This reduction in initiation of outgrowth was found to result from inhibition of bud activity rather than from loss of bud viability. As very few axillary buds in pastures are buried from emergence, it was concluded that stolon burial has little impact on the initiation of outgrowth of axillary buds in pastures. Severe deprivation of photosynthate or phosphorus within plants, induced by shading or low phosphorus supply, respectively, delayed the initiation of outgrowth of axillary buds until they were positioned six or more nodes from the stolon apex, and reduced node appearance rates which further delayed initiation of outgrowth. However, such deprivations of resource did not change the proportion of buds that eventually initiated outgrowth. Thus together, these experiments showed that increases in apical dominance (delay in initiation of outgrowth of axillary buds) could be induced by either low levels of intraplant resource or in response to sensing of the environment. If the inhibition of axillary bud outgrowth was maintained until a bud was positioned more than eight nodes from the apex, that bud would not initiate outgrowth upon an improvement in plant growing conditions. It is suggested that there is a 'window of opportunity' for initiation of outgrowth of axillary buds limited to those nodal positions eight or less from the apex not subjected to inhibition through apical dominance. Relationships between potentially available photosynthate within stolons and branching were further explored by measuring the starch, sucrose and hexose contents of individual internodes of stolons subjected to burial/defoliation treatments or differing seasonal growth periods and correlating these contents with branching activity of the distal axillary bud. There was no evidence to suggest that photosynthate supply was limiting branching in these pastures. Starch content of stolons varied five-fold with season (minimal and maximal contents occurring in late spring and early autumn, respectively). This seasonal pattern in the availability of stored photosynthate within plants provided a physiological basis to underpin understanding of the very significant changes that occurred both within individual plants and populations of white clover in pastures during the early spring to mid-summer period. Such changes centre on a rapid increase in growth demand for photosynthate in early spring which decreases the starch content of stolons, whereupon stolon senescence increases markedly thereby fragmenting plants and thus reducing branching complexity and mean dry weight per plant. The change in status of the white clover population in spring was considered to negatively influence the response of populations to cultural and environmental perturbations during late spring - early summer. It was concluded, in view of the large changes occurring within white clover populations in spring-early summer, that the greatest of the effects of stolon burial, which was an increase in the mortality of recently initiated branches during winter (a period of low growth rate), would not have major implications for the population dynamics of white clover in this environment. However if burial of a high proportion of stolon material occurred in summer it would have greater potential to significantly reduce branch establishment within populations.