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Introgression of the beta-carotene locus into rice living marker-assisted backcrossing
Thesis Abstract:
Malnutrition and hidden hunger due to deficiency of micronutrients is a severe problem in the world, especially in developing countries. Vitamin A deficiency (VAD) is widespread in South and Southeast Asia, which are the major rice-eating regions. Golden Rice was genetically modified to produce β-carotene in the rice grain to combat VAD. However, Golden Rice variety (Kaybonnet) with psy gene from corn was produced in japonica background. This variety is not adapted to the tropical conditions. Moreover, japonicas are not preferred by most Asian rice consumers. Therefore, we are in the process of introgressing the b-carotene locus from Kaybonnet into popular indica type Asian rice varieties such as IR64 using marker-aided backcrossing (MAB).
Marker-aided backcrossing was used to transfer β-carotene locus from a transformed japonica donor variety Kaybonnet into IR64 as it has many advantages such as efficient foreground selection, efficient background selection, minimum linkage drag around the target locus, and rapid reconstruction of recipient genome. Molecular markers (STS) for the target transgene and 89 SSR markers evenly spread over the rice genome were used to monitor the introgression of target locus from the donor variety Kaybonnet and quantifying the recurrent genomic contribution of the recipient variety IR64 in the process of backcrossing. In the study, BC2F1 and BC3F1 generations were advanced from BC1 generation using MAB along with phenotypic selection. In BC1 generation, the maximum proportion of genome was 93 percent while in BC2 generation, one plant had 100 percent of genome of the recurrent parent for the target chromosome. Clearly, MAB was more efficient than phenotypic selection as the expected proportion of recurrent genome in BC1 and BC2 generation is 75 and 87.5 percent, respectively. BC3F1 and BC2F2 seeds of selected plants are available to carry out further breeding until agronomically superior plants homozygous for β-carotene locus in the IR64 background are produced.