Somaclonal Variation in Inbreds and Testcrosses of Maize (Zea Mays L.) and the Possible Involvement of Transposable Elements
Williams, Mark Edward
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https://hdl.handle.net/2142/72610
Description
Title
Somaclonal Variation in Inbreds and Testcrosses of Maize (Zea Mays L.) and the Possible Involvement of Transposable Elements
Author(s)
Williams, Mark Edward
Issue Date
1988
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Abstract
The culture of plant cells in vitro results in the accumulation of genetic and cytogenetic modifications in both the cultured cells and plants regenerated from them which has been termed "somaclonal variation". The primary objectives of this research were to evaluate the amount of somaclonal variation in quantitatively inherited characters at both the inbred (R$\sb2$ family) and hybrid (R$\sb1$ x tester) levels and, using the well-characterized Ac element as a model, examine at the molecular level one possible mechanism of this somaclonal variation, the activation of endogenous but quiescent transposable elements following passage of cells through tissue culture.
Using the inbred line FR27rhm, significant somaclonal variation was produced in R$\sb2$ families in seven of the eight quantitative characters measured, including days to silk, yield per plant, ear height, ear number, kernel row number, weight per 100 kernels and ear length; the only exception was tassel branch number. Although most of the variation created was deleterious in nature, one R$\sb2$ family was present which yielded 15 percent higher than the highest S$\sb2$ family. Twenty-six of the twenty-eight correlations between the eight characters were significant; all of the other characters were significantly correlated (positively or negatively) with yield per plant. Most of the changes due to somaclonal variation are mutations that cause a general reduction in plant vigor observed over several characters in the same family.
At the hybrid level, FR27rhm R$\sb1$-plant x FR303 crosses significantly higher in grain yield and/or lower percent grain moisture but not for percent stalk lodging relative to uncultured FR27rhm x FR303 crosses were observed at frequencies highly in excess of what should be expected on the basis of random chance.
Contrary to published experiments, all genotypes examined, Oh43, Al88, Al88 x Oh43, FR27rhm and 79-R4443 possess the 2.5 kb PvuII-Ac fragment but do not contain active Ac elements. A change in the genomic positions of Ac-homologous sequences, which should accompany Ac activation, was observed in only one of the 57 R$\sb0$ and R$\sb2$ plants tested. Thus, while Ac element mutagenesis may contribute to somaclonal variation, it appears to be a relatively rare event.
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