Typescript (photocopy). / Digitized by Kansas Correctional Industries

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Maize defective kernel (dek) mutants identify genes necessary for the successful passage of embryos through the embryogenic and maturation phases of embryo development. The goal of this thesis was to characterize the developmental potential of three dek mutants that appeared to be morphologically blocked prior to the maturation phase of embryogenesis. Descriptive and experimental studies of the mutants and their wild-type counterparts were used to compare their morphological and physiological progression through seed development. Parameters of growth, morphogenesis, maturation and germination were measured throughout their ontogeny. Two mutants, cp*-1311C and cp*-1399A, slowly progress to morphological stages 2 and 3, respectively. Growth and maturation processes remain in synchrony with morphology, as indicated by their size, germination behavior and level of storage reserve accumulation. Not every facet of development is retarded. Both dehydration of the seed and the accumulation of desiccation proteins, maize Lea group 3 (MLG3) and Lea group 2 dehydrin (DHN), are more globally regulated, since their accumulation is precocious with respect to embryo morphology. This suggests that some aspects of the embryonic program are mediated by maternal factors. Genetic and developmental characterization of a third mutant, dks8, indicates that it defines a pattern gene that functions to specify the initiation or maintenance of the embryonic shoot. The dks8 mutant is variable in phenotype; mutants with partial and abnormal shoot development are sometimes found on ears segregating for shootless dks8 embryos. dks8 is not allelic to other shootless dek mutants. The dks8 mutation was isolated from an active Mutator transposon stock. RFLP analyses for cosegregation of various Robertson's Mutator transposable elements with the dks8 allele demonstrate that a Mu8 element and dks8 are closely linked. The dks8 allele is under-represented on segregating ears, which may reflect either epigenetic suppression of the mutant phenotype or a bias against the mutant allele in the formation of the female gametophyte. / Graduation date: 1995

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 223-229). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 223-229). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M.Sc.Agric.)(Agronomy)--University of Pretoria, 2009. / Abstract in English. Includes bibliographical references. Available on the Internet via the World Wide Web.

Maize production in short-season environments has at least two critical problems. Firstly, maize grown in short-season areas has lower leaf area indices (LAI) than maize grown in long season areas, due to shorter plant stature and less time for development, which results in reduced leaf number and size. Secondly, in very short-season areas the seasonal thermal-time available may be insufficient to mature grain of current maize hybrids. Therefore development of maize types that accumulate leaf area and mature quickly would increase production of maize in mid- to short-season areas. The leafy (Lfy1) and reduced-stature (rd1) genes make contributions to this end. However, these two genes have not previously been combined. From 1991 to 1993, field experiments were conducted to evaluate the leafy reduced-stature (LRS) inbred lines and hybrids for yield, maturity times and morphological traits, at different planting densities and patterns in Montreal and Ottawa. LRS maize inbred lines showed the most rapid silk extrusion, optimum leaf area development, and rapid growth of the first ear, the highest yield per unit leaf area, and the closest synchronization of pollen shed and silk extrusion at high plant population densities. LRS maize hybrids had the most rapid leaf development, longest grain filling period, lowest grain moisture content at harvest, and highest harvest index. Therefore LRS hybrids should allow an extension into shorter season areas where it can not now be successfully cultivated, and may increase yields in mid- to short season areas where maize is now produced.

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