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|Title:||Systematic and Cytogenetic Studies of the Genus Zea|
|Department / Program:||Agronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Teosinte and maize were divided into four species on the basis of morphology. Zea luxurians, Z. diploperennis, and the tetraploid Z. perennis were grouped under section Luxuriantes, and Z. mays was included in section Zea. Zea mays includes subsp. mays (cultivated maize), subsp. mexicana, and subsp. parviglumis (var. parviglumis and var. huehuetenangensis). To determine the feasibility of transferring agronomically useful characteristics from teosinte to maize, and to establish evolutionary relationships among Zea taxa, chromosomal affinities and pollen fertility in hybrids, patterns of heterochromatin (C-bands) in chromosomes, and electrophoretic patterns of seed proteins and seedling isozymes were studied. Hybrids between teosinte and maize were relatively easy to obtain. A high degree of chromosomal affinity was observed among all taxa at diakinesis, and pollen fertility was not seriously reduced, providing little barrier for gene transfer. Compared with the parents, the number of chromosome arms bound in 20-chromosome hybrids involving either Z. diploperennis or Z. luxurians, except Z. luxurians x var. huehuetenangensis, was significantly reduced. Chromosomes of Z. diploperennis and, to a lesser degree, those of subsp. mays displayed close homology to chromosomes of the tetraploid Z. perennis. Based on C-banding patterns, two groups of Zea taxa could be distinguished. Zea perennis, Z. diploperennis, Z. luxurians and var. huehuetenangensis have terminally located heterochromatin. The remaining taxa have both terminal and sub-terminal heterochromatin. Isoelectric focusing patterns of seed proteins clustered all taxa of section Zea, clustered Z. diploperennis with Z. perennis, and placed Z. luxurians between these groups. Seedling isozyme patterns do not correspond completely with the morphological classification. It was concluded that Z. luxurians and var. huehuetenangensis are more closely related than implied by placement in different sections, that recognition of two teosinte taxa as varieties of subsp. parviglumis is questionable, and that Z. perennis is an autotetraploid derivative of Z. diploperennis.
A tetraploid maize was studied to determine whether cytological changes accompanied the 30% increase in seed set obtained after 22 years of selection. No changes were detected in number of multivalents. Selection for fertility as a heritable unit, and against unbalanced gametes were hypothesized as explanations for the increased seed set.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
|Date Available in IDEALS:||2014-12-16|