Genetic differences, extent of hybrid vigor, nature of gene action, heritability estimates, and associations among characteristics, and between progenies and their respective mid-parents were determined for seed and plant characteristics in white clover (Trifolium repens L.). Ten seed and seedling vigor characteristics, including seed weight, ATP content in seed, seed respiration, and seedling vigor index were studied for a diallel cross consisting of 28 single crosses, five test-crosses, four checks, and eight open-pollinated seed and seedlings. Twenty-three plant characteristics on stolon, petiole, leaf, and forage were examined on the eight clones diallel cross, five test-crosses, three checks, the eight parental clones of single crosses, and six parent clones of the test-crosses. These 14 parent clones for this study were assembled on the basis of diverse morphology and origin. Most seed and seedling vigor characteristics, except RQ values, and most plant characteristics, except internode length, LAR and diurnal ratio in SLW, expressed significant differences among and within most groups of progenies and parental clones. All seed and seedling vigor characteristics, except RQ values, responded primarily to the nonadditive type of gene action. This suggests that the plant breeder should design his breeding program to develop varieties where hybrid vigor can be used to advantage. Among the criteria used in this study to measure seed and seedling vigor, ATP content per seed was closely associated with seedling vigor index and with certain plant characteristics, including forage yield per plant. The associations of seed weight with other seed and seedling vigor characteristics were negative or poor. Most plant characteristics showed apparent hybrid vigor when progenies were compared with their respective mid-parents. With few exceptions, most plant characteristics, stolon, petiole, leaf and forage yield per plant, responded primarily to the nonadditive gene system. This indicated that the plant breeder may use the hybrid approach to white clover variety development. The exceptions were leaf ratio and SLW which responded primarily to additive gene action, and area and dry weight per leaf appeared to respond equally to additive and nonadditive gene action. Genetic differences were more readily identified for stolon number and length when measurements were taken after 70 days of growth. Yield components, such as number, length, and diameter of stolon, petiole length, number of leaves per plant, and dry weight per leaf were closely related to each other. The leaf components of yield, dry weight per leaf and number of leaves per plant, had the highest direct and indirect effects on forage yields per plant among the yield components. This study showed nonadditive gene action primarily responsible for most seed and plant characteristics. Considering the ease of vegetative propagation in this species along with the self-incompatibility, mechanisms, it is suggested that parent geneotypes may be developed by some recurrent selection procedure, then crossed on a two clone synthetic basis to form experimental lines for testing purposes. / Graduation date: 1973

In the Creston valley in southeastern B.C., intermediate white clover is grown for seed and is a useful crop in farm field rotations. For several years seed yields have been declining, and despite good prices and markets, hectarage to white clover is declining. In 1976, work was initiated to determine some of the factors responsible for the decline in seed yield and hectarage. At the same time, an exploratory study of the genetic variation in the seed stocks of the valley was instituted in the hope that a Creston strain might be characterized or selected. In 1977, in the Creston valley, a series of replicated plots in six fields, representative of the edaphic, climatic and management regimes, were established to measure seed and forage yields and losses from multiple sources. At the University of B.C., four hundred individual plants representative of twenty sources, including some Creston sources, and encompassing substantial genetic diversity, were established from seed in replicated uniform nurseries. In an adjacent nursery one hundred and eighty Creston clones were established. Observation and measurement of a number of characters were taken on all plants several times during the growing season. Average clean seed yields on the Creston experimental plots ranged from 468-972 kgs. per hectare (418-868 lbs per acre). Farm yields of clean seed, by contrast, ranged from 262-491 kgs per hectare (240 to 450 lbs per acre). It was estimated that of the loss in seed threshed (dockage) , but not cleaned, 3-10% was insect damaged; loss attributable to farm harvesting procedures was estimated to reach 50%. Losses in the developing crop are difficult to assess quantitatively but appeared to be very serious. To offset these losses, in recent years, producers have been reducing the length of white clover ley and are now in most cases obtaining one seed crop only in the year after establishment; this practice, if carried on without counter selection, might result in a biennial habit. Three species of weevil appeared to be the most serious pests, viz. the clover root curculio (Sitona hispidula Fab.), and the clover seed weevil (Miccotrogus picirostris (F)) and the lesser clover leaf weevil (Hypera nigrirostris Fab.). The population peaks of the adults apparently occur at different times in the season. Currently only one aerial application of malathion is applied in June to control the clover seed weevil. Almost all roots examined bore signs of larval feeding, doubtless due to the clover root curculio; root nodules, abundant in spring, diminished rapidly as the season progressed. Measurements of nitrogen fixation, using the acetylene reduction technique and the Kjeldahl N-determination, were incomplete. Flower frequency and development, flower colour, leaf area, petiole length, leaf markings, plant height and weight, and prussic acid levels were some of the characters measured and observed on the individual plants, established in the U.B.C. nurseries from Creston and other sources. Not unexpectedly, the Creston stocks possessed a measure of distinction from most other stocks of intermediate white clover; nonetheless, there appeared to be ample variability in the Creston stocks within which to select strains to meet at least two needs of the region - viz. a) plants useful in the revegetation of ranges and of unstable soils, and b) plants well adapted to the arable long ley pastures of the humid and sub-humid areas. / Forestry, Faculty of / Graduate

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The theory of Evolution by Natural Selection deals substantially with events now past, and with processes too slow for contemporary study. Experimental studies of evolution are possible, but are liable to the criticism that they deal with artificial, or at least extreme and atypical situations, involving rapid evolutionary change. Such criticism can be avoided to a degree by studying situations now in equilibrium. It is suggested that interesting results may be obtained by studying polymorphisms, and comparing the equilibria reached in populations of an organism in different environments. The chosen approach was to find a case of polymorphism convenient to study, followed by an attempt to interpret the pattern of its variation in terms of features of environments where a morph was common selecting in its favour, and vice versa. The material presented falls into three parts. 1) Material and Methods: Background and Preliminary Studies. The system chosen for study was the white V-shaped leaf markings of Trifolium repens. The species is widespread, abundant, and variable; the character is expressed on vegetative organs, and is therefore always accessible; and the known variation in this character had already been interpreted in terms of the action of a set of several alleles at one locus. The results of crosses indicate general agreement with previous reports. One heterozygous plant apparently largely failed to transmit one allele, V^b, through the pollen. Segregations indicate that a new phenotype, 'smeared', is determined by a particular V^h allele. Two more new phenotypes, 'shaded' and 'marginal' are described. The places where these and other rare phenotypes have been found are listed. New reports and the author's other experience are combined with previous reports in a new general account of leaf marking in the species, which also deals with at least three distinct classes of red markings. There appears to be more variation, implying more alleles, than previous accounts allow for, and reportedly distinct types, for example, V^h, V^l and V^f, seem to be linked by a series of intermediates, among which clear dividing lines are hard or impossible to draw. Experimental studies relating to the techniques of population sampling are reported. Scarification by 10 to 20 minutes exposure to concentrated sulphuric acid was chosen to deal with hard seed. The effect of a restricted number of mother plants on the accuracy of a seed sample is discussed; predictions concerning the frequencies of different types in progeny from single heads grown separately were roughly consistent with observations. Possible differences between vegetative and seed samples are discussed. Morph frequencies in a sample of plants bearing inflorescences were not found to be significantly different from those of the whole vegetative sample. The consequences of this species' ability to reproduce vegetatively are discussed, and a brief clone-mapping project is described. The procedures used to obtain and score material, and to obtain information about its background are described. The amounts of material of different types from different sources is summarised in Table 6.2. Problems involved in estimating gene frequencies are discussed, and the derivation of the values used to represent the different morph frequencies is outlined; they are basically phenotypic frequency figures, gene frequency calculations being used only where it was found to be necessary. 2) Observations on Population Samples. Polymorphism in respect of white leaf marks was found to be present in all except 15 out of 624 samples. The commonest group of phenotypes are the 'simple V-marks', referred to as 'L'. The next commonest is the unmarked type, 'O', present in all except 72 out of 624 samples, with an overall frequency among the plants scored of 17 per cent. Study of the sample data reveals a deficiency of the double marked phenotypes expected to be showed by V^byV^l plants. This is explained as the result of a degree of dominance of V^by in such combinations; the effect of such dominance is allowed for in the frequency figures representing the frequency of 'L' marks, and of double-marks containing two members of the 'L-series' of simple-V-producing alleles. The possibility of demonstrating interaction between the frequencies of different morphs is discussed. There are indications of lower frequencies of 'By', 'B', and 'F' marks when the unmarked phenotype is common. The possibilities for the main object of the work, discovering associations between morph frequencies and environmental factors are shown in Table 8.1, giving the sets of data presentable for particular methods of analysis. Data on 148 British samples, scored in the field by the author, were treated by Multiple Regression Analysis (using the KDF 9 Computer of the Oxford Computing Laboratory), to test for association of morph frequencies with geographical location, altitude, and soil pH. Significant increases in the proportion of unmarked plants are shown with greater distance north and higher altitude. Frequency data for all the classes of morphs described is shown in the form of maps, of the British Isles, Western Europe, and the whole of the species' natural range. These maps confirm the northwards increase in frequency of the unmarked form found in Britain. Maps for the rare morphs show various patterns, most of which seem to involve central regions of higher frequency north of the Mediterranean (France - Alps - Greece) with lower frequencies elsewhere. Regression analysis of a set of seed samples from Spain supports the conclusion from British vegetative samples of an increase in unmarked frequency with higher altitude. Examination of the information about the background of other samples suggests higher unmarked frequencies in pastures than on waste ground, meadows being intermediate. British data suggest an association with wet, and particularly with badly-drained sites, with trodden paths, and with dense vegetation. There are patterns of response to water regime elsewhere but (e.g. Polish data) they tend to suggest the opposite association, of high unmarked frequency with dry conditions. 3) Comparison with other species. New observations are reported on some other related species. Available information on marking in other species of Trifolium is reviewed, and it is pointed out that it is scattered, difficult of access (much unpublished), and sometimes ambiguous or contradictory. Summary of this data indicates the presence of white V-markings in nearly 30 species of Trifolium, and its absence in at least as many more. Marks are probably entirely absent in subgenus Chronosemium and perhaps in part of subgenus Trifolium. but seem to occur in most of the other subgenera for which there is information. When marks are present, it appears that they are nearly always variable. Only three species are definitely reported as always marked, and in two of these there is variation between different types of marking. This suggests that the factors producing or preserving polymorphism in T. repens act also in other marked species. The presence of red leaf marks of various kinds is reported in 21 species of Trifolium. Also in the tribe Trifolieae, both red and white V-markings are found in Parochetus communis. Material grown by the author showed great variability within each plant in leaf mark, but no clear differences between plants. Red leaf marks, variable, and in some cases approaching a V-shape, are also found in Medicago. Several lines of evidence indicate relationships between the white markings, and the various red marking systems in T. repens. It is suggested that the white and red V-markings have a common evolutionary origin. Some examples of leaf marking with analogous properties in genera unrelated to T. repens are also briefly reviewed. In discussion some possible challenges to the validity of the results claimed are discussed, and evidence is presented suggesting that the reported genetic clines in unmarked frequency are real. Selective factors affecting unmarked frequency are tentatively suggested to be temperature and water regime. The problem of relating these to markings on leaves is discussed, and also the possibility that the phenomena of leaf marking are by-products of unknown processes, and are of no intrinsic importance. It is suggested that the inter- actions between red and white markings support the hypothesis that leaf markings themselves are of selective importance; and some possibilities as to what form this selective importance might take are mentioned. Possibilities for further work indicated in the course of the studies presented here are discussed. They include studies on important problems of population dynamics, which affect the design of techniques for sampling for leaf markings, but in which also observations on leaf markings could be used as means to ends of wider significance. Ways in which the methods used in the present study could be improved in a repeated study are suggested; however, it is felt that the clines observed provide a starting point for experimental work, and that this might be more rewarding than further descriptive work.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains ix, 101 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 78-87).

Thesis (Ph.D.) -- University of Adelaide, Dept. of Plant Science, 2000. / Bibliography: leaves 213-229.

Thesis (M. Agr. Sc.) -- Lincoln University, 2008. / Also available via the World Wide Web.

A white clover ( Trifolium repens ) system, based on one ozone-sensitive (NC-S) and one ozone-resistant (NC-R) clone, has been developed as an indicator to estimate the effects of tropospheric ozone on plant biomass production. A reduction in the vegetative biomass ratio (NC-S/NC-R) of the clones was correlated with increasing concentrations of ozone during a 28-day exposure period. However, the mechanism of ozone sensitivity or tolerance at the biochemical or molecular level is not known. Superoxide dismutase isozyme activities in the two clones did not respond differently to ozone treatment. However, catalase activity increased somewhat more in the leaf tissue of NC-R, compared to NC-S, after ozone treatment. Two-dimensional polyacrylamide gel electrophoresis (PAGE) showed the presence of two proteins (Ozone-Response-Proteins, ORPs) that were more responsive to ozone in the tolerant genotype than in the sensitive one. After ozone treatment for three days, the ORPs were four-fold higher in leaf tissue of NC-R compared to NC-S. Also, the amount of the ORPs was twenty-fold higher in leaf tissue of ozone-treated NC-R than in that of control NC-R. These proteins have apparent molecular weights of 21.5 kD and 23 kD and isoelectric points of 4.1-4.4 on SDS-PAGE gels. The filtrate of a 100 kD concentrator showed that the native molecular weights of the ORPs were less than 100 kD. The results obtained from a study of field samples demonstrated that protein content in leaf tissue of both NC-R and NC-S was positively correlated with ORP content. / Master of Science