Transferring Cocodrie-derived golden rice locus into BR29 (Oryza sativa L.) using marker-assisted backcrossing

Introgression of the Beta-carotone locus from Golden Rice 1 Cocodrie-event 146 to an indica variety BR29 was done using marker-assisted backcrossing (MAB). Four previously developed BC1F1 plants served as initial population for the study. Effective foreground selection was done using Beta-carotene locus-specific primers and phenotypic characterization of the seeds. Three-hundred thirteen out of the 688 BC2F1 plants showed the presence of the introgressed gene, 67 of which came from the most promising BC1F1 plant-no.20. Positive plants were subjected to 2-stages of background selection to estimate the percentage of the recurrent parent genome (RPG): 82.02 to 89.89% for the BC2 and 93.26 to 98.89% for the BC3 generations. The two rounds of selfing in the BC3 helped in fixing the introgressed gene in the homozygous state in a new genomic background. After 3 backcrosses, the selected lines have phenotypic similarity with its recurrent parent. No significant differences were observed among the transformed lines with that BR29 for all the recorded agronomic traits as BC3F2 as well as in BC3F3 generation except for the 1000 grain weight (t test). A set of 15 BC3F3 advanced introgression lines originating from a single BC1F1 plant had % RPG values between 92.13 to 97.75% with no significant differences in various phenotypic traits from BR29 and with total carotenoids ranging from 4.3 to 5.3 ug/g in the grains. The study showed the effectiveness of marker-assisted backcrossing in selecting the progenies containing the introgressed gene, accelerating the recovery of RPG, and selection of advanced lines that fully express the accumulation of the carotenoid in the grains. Further testing of the introgressed progenies in a randomized replicated field trial is planned in the near future to select the best progenies for multi-location testing.