M.Sc. (Botany) / Please refer to full text to view abstract

Genomic selection (GS) has been adopted by the dairy cattle breeding industry and the opportunity exists to implement this technology in UK beef and sheep breeding. However, these sectors do not appear so readily predisposed to GS implementation. Following an introduction to GS in Chapter 1, Chapter 2 investigated the structure of the little-studied UK beef breeding sector. This provided estimates of key commercial and pedigree population parameters, for use in modelling genetic gain from GS. Terminal traits were found to be the dominant selection goals, with 85% of beef-sired commercial matings resulting in progeny being slaughtered at a prime age. Pedigree bulls disseminated the majority of genes in the sector via natural service. The correlation between the terminal selection index (TI) and the sale price of breeding bulls was moderate, suggesting a modest uptake of genetic technology in the sector. Chapter 3 estimated selection intensity for TI, generation interval and the dissemination rate of improved genes in the pedigree Limousin population. In order to predict the genetic gain achievable in using GS in beef and sheep breeding, Chapters 4 to 6 undertook deterministic selection index simulations, incorporating genomic information as correlated traits. In Chapter 4, GS was modelled for terminal beef traits, when incorporating carcass information and accounting for likely genotype by environment interaction. Using a training population of 2000 sires, this concept was predicted to offer 40% greater genetic gain than existing BLUP selection using pedigree phenotypes. Gene flow methodology projected the commercial value of this gain to offer a substantial return net of genotyping costs. Chapter 5 explored GS for maternal beef traits within the concept of a nucleus breeding scheme. Whilst greater genetic gain was predicted with GS than with conventional BLUP, the economic value of this gain was projected to be too low to justify such a scheme in the UK. Chapter 6 proposed a synergy between computer tomography (CT) phenotypes and GS in sheep breeding. Developing a genomic predictor from male selection candidates with CT phenotypes and conventional performance records was predicted to increase genetic gain by 55% over BLUP selection without CT traits. Introducing GBV contributed most of the accuracy in this scenario, suggesting that the existing performance recording structure in UK sheep breeding could in the future be replaced by GS using CT. In the general discussion, the potential for GS in other beef and sheep traits was considered in the light of the outcomes of these simulations. Given the lack of vertical integration in UK beef and sheep sectors, the drivers for implementation of GS are examined. Finally, the options for international cooperation and the possibilities offered by future genotyping technology are considered. It was concluded that implementation of GS incorporating beef carcass phenotypes was merited and could provide a platform for future GS implementation in other novel traits. Sheep GS with CT traits was considered a higher risk strategy, due to the lack of evidence for uptake of existing EBV technology.

No description available.

Four species of the genus Parthenium were involved in a hybridization attempt. The species were: guayule (Parthenium argentatum Gray), Parthenium fruticosum Less, Parthenium bipinnatifidum (Ortega) Rollins, and Parthenium incanum H. B. K. Primary attention was given to the formation of hybrids between P. argentatum and P. fruticosum. Characteristics of the latter species such as size, growth rate, possible disease resistance, and wider geographical adaptation were desirable for transfer to P. argentatum. Reciprocal crosses were made between these two species and the production of hybrids was not difficult. However, in the case of selfing, backcross and sibcrosses, germination percent was 0.86 from a total of 3,471 achenes. Therefore, a search for the cause or causes of the negative results was initiated. The factors which were considered of primary interest were: incompatibility, genic and chromosomal sterility, pollination and planting techniques, and seed germination treatment. Incompatibility was considered the main limiting factor in the formation of a backcross population. Rubber analysis was performed in the interspecific hybrids. Mean rubber percent for hybrids between P. artentatum and P. fruticosum was 1.19; and for the reciprocal cross it was 0.39. Hybrids of the cross P. fruticosum x P. bipinnatifidum had a mean rubber percent of 0.19.

No description available.

No description available.

Photocopy of typescript / v, 177 leaves, 6 leaves of plates : ill. (part col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.) Dept. of Agronomy, University of Adelaide, 1981

Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The exomorphology and size of Leucadendron pollen was examined using a scanning electron and light microscope respectively. Pollen was found to have a consistent triangular shape with three apertures. Pollen grain size however, show difference between species, sections and subsections on Leucadendron. Pollen of all species examined had a woven appearance like the intertwined threads of a fabric with orbicules present on the surface of L. chamelaea, L. elimense subsp. elimense and L. galpinii. Pollen viability was successfully assessed using a solidified agar medium containing 2g agar and 109 sucrose. Pollen germination for all species was found to be above 55% viability. A diallellayout of crosses has demonstrated conclusively that fecundity differs when crossing between species of the genus Leucadendron. Artificial hand pollination was applied successfully on Leucadendron and showed repeatedly that seed set following intraspecific crosses between the male and female inflorescence of the same species gave the same high rate of seed set as found in nature. However, seed numbers declined sharply when crossing between species of the section 'Leucadendron'. Seed set following crosses between species of different sections or sub-sections was the lowest and in most cross combinations there was no seed harvested or no seed germination. The diallellayout was useful in identifying incompatible species and for locating possible incompatibility barriers to interspecific seed development. The morphology of the stigma was examined with a scanning electron microscope. Stigma appearance of all species had a consistent round to oval shape, except for L. rubrum, which had an elongated shape. Stigma surfaces of all species were densely covered with a large number of unicellular papilar cells on the swollen base. The aniline blue staining technique, together with the fluorescent microscope technique was used to follow the growth of the pollen tube following compatible and incompatible cross combinations. Pollen on the stigmas of compatible and incompatible species examined showed signs of germination. Pollen tubes grew between the papilla cells in all directions and only the most vigorous ones reached the upper part of the style. From the upper region of the style, yellow green tubes grew cohesively in the middle of the style towards the ovule. In compatible combinations a not more than 4 tubes reached the ovule region, but was difficult to observe when they entered the micropyle for fertilization. In incompatible species a large number of abnormalities occurred beyond the upper region of the style. / AFRIKAANSE OPSOMMING: Die morfologie en grootte van Leucadendron stuifmeel is deur middel van 'n skandeerelektron - en ligmikroskoop bestudeer. Baie klein verskille in stuifmeel morfologie het voorgekom. Diverse verskille in stuifmeelgrootte het wel voorgekom tussen spesies, groepe en subgroepe van Leucadendron. Stuifmeelvorm was deurgaans driehoekig en die oppervlakte van die stuifmeelkorrel het die voorkoms van geweefde vesels gehad. Klein, bolvormige struktuurtjies was teen verskillende digthede oor die stuifmeeloppervlak van L. chamelaea, L. elimense subsp. elimense en L. galpinii versprei. Stuifmeelkiemkragtigheid is bepaal deur dit op soliede agar medium te ontkiem en was deurgaans bo 55% kiemkragtig. Onderlings dialleliese kruisings van Leucadendron spesies het variasie in saad set getoon. Handbestuiwing is suksesvol uitgevoer en saadset in intraspesie kruisings hoog en soortgelyk aan natuurlike bestuiwing. Saadset en saad ontwikkeling het drasties verswak toe verder vewante spesies as ouers gebruik. As gevolg van hulondeurdringbare saadhuid is neutagtige sade gewoonlik moeiliker ontkiembaar. Die diallel uitleg was ook nuttig om verenigbare en onverenigbare kruisingskombinasies te identifiseer en om onverenigbaarheidskanse op te spoor. 'n Skandeerelektronmiskoop is gebruik om die morfologie van die stigma te bestudeer. Stigmas was deurgaans rond tot ovaalvormig, behalwe die van L. rubrum wat 'n verlengde voorkoms gehad het. Die stigma bestaan uit 'n groot aantal eensellige papilla, wat dig teen mekaar gepak is op 'n geswolle basis. Aniline-blou fluoresserende kleurstof en 'n fluoressensie mikroskoop is gebruik om die pad van die stuifmeelbuis in verenigbare en onverenigbare kruisingskombinasies in Leucadendron te volg. Stuifmeelontkieming het in alle kruisingskombinasies geskied. Stuifmeelbuise het in alle rigtings tussen die papilla gegroei en slegs die mees kiemkragtige stuifmeelbuise het die boonste deel van die styl bereik. In die styl het die buise dig teen mekaar gegroei en was dit moeilik telbaar. 'n Maksimum van vier buise het die vrugbeginsel bereik, maar dit was moeilik om verder te volg nadat hulle die poortjie bereik het. In onverenigbare kruisingskombinasies het stuifmeelbuise abnormale groeipatrone in die boonste gedeelte van die styl getoon.

Typescript, etc. / Digitized by Kansas State University Libraries

Typescript. / Digitized by Kansas State University Libraries