Graduation date: 1993

No description available.

In response to environmental concerns about NO3- leaching research has shifted toward the increased incorporation of nitrogen-fixing legumes, such as red clover, into agroecosystems to promote tighter cycling of nitrogen (N). Although more sustainable than fertilized systems, red clover still has the potential to contribute to leaching. The objective of this study was to ascertain the contribution of red clover to soil NO3- when grown in mixture with bluegrass. Soil solute samples were collected at 15 and 45 cm depth using ceramic suction lysimeters from two experimental pastures in Nova Scotia in 2009. The concentration of NO3--N in the soil solute of bluegrass-red clover mixtures was 10 to 25 times higher in Truro, and 5 to 16 times greater in Nappan, compared to the corresponding unfertilized pure bluegrass stand. Neither sub-surface irrigation nor two distinct red clover cultivar mixtures were found to significantly alter NO3- leaching patterns.

Genetic variation within and between two cultivars of red clover (Trifolium pratense L.), Essi from Europe and Ottawa from Canada was estimated using morphological, isozyme and random amplified polymorphic DNA (RAPD) markers. A total of 21 enzyme-coding loci with 43 alleles was detected using twelve enzyme systems. The mean number of alleles per locus was 1.81 in Essi and 1.67 in Ottawa. Nine 10-mer primers were used to assay 20 individuals from each cultivar for RAPD markers. Each primer gave from 7 to 20 amplified bands with an average of 14.8 bands per primer. High within-cultivar variation was observed in both cultivars using both isozyme and RAPD markers. The mode of inheritance of seven isozyme loci: Aat-2, Amy-1, Est-4, Est-7, Pgd-1, Pgd-2 and Skd-1, in red clover was verified. The genetic basis of banding patterns for 16 other isozyme loci: Aat-3, Adh-1, Dia-1, Dia-2, Dia-3, Est-1, Est-2, Gpi-2, Idh-1, Mdh-1, Mdh-2, Mdh-3, Mdh-4, Me-1, Me-2 and Pgm-2, was also postulated, based on the segregation patterns observed within cultivars. Two pairs of linked enzyme-coding loci, Est-4/Est-7 and Pgd-2/Skd-1, were found with joint segregation analysis. Estimates of genetic variability of 15 red clover cultivars from three different origins indicated that within-cultivar variation was much higher than between-cultivar variation. Allele frequencies of these isozymes could discriminate the five North American cultivars assayed, but they could not differentiate cultivars from Europe and Japan. The use of RAPD markers obtained from bulked samples was investigated for cultivar identification in red clover. Pooled samples were examined in order to minimize variation within cultivars. Twenty was found to be an appropriate number of red clover individuals per bulk for homogenizing genetic variation within cultivars. Fourteen 10-mer primers were used to amplify genomic DNA from combined leaf samples of 15 red clover cultivars from European, Japanese and North American origin

Phenotypic characterizations demonstrated that diversity among 19 naturalized North American and 5 commercial Kura clover ( Trifolium ambiguum M.B.) rhizobial strains was limited. Growth chamber and field evaluations indicated the superiority of North American isolates, increasing foliage accumulation by 30% when compared to commercial inoculant strains. Nitrogen fertilization, however, produced greater accumulations in all evaluations. Genetic diversity among 128 isolates from the lower Caucasus was significant. Nodulation specificity of rhizobia from the lower Caucasus was demonstrated to be more complex than what was reported in the literature, as plants of different ploidy levels and even of different species were, in some cases, nodulated by the same isolate. Specificity of a given rhizobial strain varied depending on the isolate. This study identified naturalized North American rhizobial isolates that are more efficient than currently used commercial strains and increased the genetic diversity of Kura clover rhizobia currently available.

The problems associated with the use of white clover in pastures in the eastern high potential areas of South Africa i.e. high P requirements, low tolerance to high Al levels and low pH in the soil as well as a limited survival time of approximately 30 months, were identified and found to be related to the inadequate root system of white clover cultivars. During the improvement programme cultivars available on the world market were introduced and evaluated under dryland conditions. Selections were made from these introductions on the basis of root conformation in high AI, low pH soils, their response to grazing and induced moisture stress. A laboratory technique for the improvement of Al tolerance was developed and the tolerance of white clover plants to high levels of Al was improved but due to the complexity of pasture plant improvement it was decided that the selection for tolerance to Al could be more effectively carried out in the field. The effectiveness of vesicular arbuscular mycorrhizas as phosphate gatherers indicated that local strains of mycorrhizas combined as effectively with white clover as the imported strains. As no seed production of white clover is undertaken in South Africa guidelines for local seed production were also established. As a result of the improvement programme, Trifolium repens cv. DUSI was developed as an open pollinated synthetic variety, based on thirty eight selected mother lines. DUSI has a greater tolerance to high AI, low pH, low P in the soil and due to an improved root system with a high percentage of secondary taproots produces better under dryland conditions and has a longer stand life than any of the cultivars of white clover available on the local market. Plant Breeders Rights were obtained for cv. DUSI and the cultivar was inscribed on the South African variety list. Limited amounts of Breeders seed have been made available to the South African Forage Seed Association for commercial seed production. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

A series of experiments was completed in which the morphology, anatomy and biochemistry of two Melilotus species, Melilotus alba and Melilotus officinalis, were studied. The purposes of the study were to illustrate whether the variability of specimens was due to polymorphism or speciation and to isolate the factors that have separated these specimens as competitors.The effects of impaction and scarification on the germination of M. alba and M. officinalis seeds were studied, as were the effects of light and temperature stimuli on germination and growth The rate of plant maturation and the chronology of flowering for the two species were investigated. Maturation differences were minor, but the chronologies of flowering deviated markedly.The techniques of one- and two-directional thin layer chromatography were used to separate the free amino acids in Melilotus seed extract preparations. The technique of polyacrylamide gel electrophoresis was used to separate the proteins in these preparations. In every experiment, the two Melilotus "species" were genus specific with no species variables in terms of the amino acid and protein complements.

Characterization of the most frequently isolated virus found during a survey of eastern Ontario red clover fields, which was designated as the Ottawa isolate, was undertaken. Determination of the biological and physico-chemical properties of the virus showed that the virus studied differed in some respects from other WCMV isolates. An ultrastructural examination of virus localization of cytopathological changes in infected red clover and pea plants revealed various types of viral inclusions, including a membrane-bound mass of tubules, not usually associated with infection by potexviruses, in red clover leaves, and severe organelle disorganization within pea leaf tissues. WCMV infection significantly reduced several processes relevant to symbiotic nitrogen fixation, including plant growth, nodulation, nitrogenase activity, leghemoglobin content, and Rhizobium population, but nitrate reductase and acid phosphatase specific activities were increased. The correlation between leghemoglobin content and nitrogenase activity shown at ten-leaf and pre-blooming stages was absent during the flowering and senescence stages. Infectivity assays, immunosorbent electron microscopy, and an ultrastructural examination showed the presence of the virus in nodular tissues; the cytopathological changes seen in bacteroids suggested that virus infection accelerated nodule senescence. Application of a cytochemical technique using diaminobenzidine showed that the leghemoglobin was located in the peribacteroidal space.

Thesis (Ph. D.)--Oregon State University, 1989. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--Dept. of Soil and Water, Waite Agricultural Research Institute, University of Adelaide, 1994. / Includes bibliographical references (leaves 146-170).