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Abstract
Abdussalam Ibrahim Ali Tayeb. Molecular Genetic Studies for Corn Resistance to Some Borers. Unpublished Doctor of Philosophy Dissertation, Department of Genetics, Faculty of Agriculture, Ain Shams University, 2003.
Eight maize genotypes were evaluated in the field for their resistance, through artificial infestation, against the corn borer Sesamia cretica. The genotypes were classified into tolerant (5 genotypes) and sensitive (3 genotypes). SDS-protein, five isozyme systems and eleven random arbitrary primers were used to detect biochemical and molecular markers for maize resistance against Sesamia insect. Protein and isozyme patterns revealed inconsistent changes in gene expression of the studied genotypes in response to the insect attack. No clear-cut markers were detected utilizing these two systems. The results of RAPD-PCR analysis indicated a high level of polymorphism among the studied genotypes. Among the 181 fragments, 178 were polymorphic among maize genotypes and three fragments were monomorphic. In this study, 28 RAPD-PCR markers for maize resistance to Sesamia cretica were detected. Eight were negative markers and 20 were positive ones. A chitinase gene (chi) responsible for insects and pathogens toxicity was isolated from an endogenous strain of Serratia marcescens. After identification, the isolated gene was introduced into a suitable vector containing the bar cassette as a reporter gene and the chi gene which was governed by the ubi promoter to be expressible in maize plant cells. A protocol for maize immature embryo transformation by biolistic (gene gun) and plant regeneration was adjusted using a DNA vector carrying the GUS gene was used for maize transformation with the chi gene. One of the studied maize genotypes, with moderate resistance to the corn borer, was used as a target for chi gene transformation. Transformed embryos were developed into plants via tissue culture regeneration. The PCR test on DNA extracted from regenerated plantlets and Basta leaf painting confirmed the integration of both of the reporter and the chi genes in some of the regenerated maize plantlets.
Key words: Maize (Zea mays L.), corn borers, resistance, RAPD-PCR, SDS-PAGE, Isozymes, molecular markers, chitinase gene, biolistic, GUS, transient expression, maize immature embryos, transformation.