Introgression of the Beta-carotene locus into rice using marker-assisted backcrossing

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 beta-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 Beta-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 Beta-carotene locus from a transformed japonica donor variety Kaybonnet into IR64 as it has many advantages such as 1) efficient foreground selection 2) efficient background selection 3) minimum linkage drag around the target locus and 4) 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 present study BCsub2Fsub1 and BCsub3Fsub1 generations were advanced from BCsub1 generation using MAB along with phenotypic selection. In BCsub1 generation, the maximum proportion of genome was 93% while in the BCsub2 generation one plant had 100% 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 BCsub1 and BCsub2 generation is 75 and 87.5%, respectively. BCsub3Fsub1 and BCsub2Fsub2 seeds of selected plants are available to carry out further breeding until agronomically superior plants homozygous for Beta-carotene locus in the IR64 background are produced.