Black Rice Developed Through Interspecific Hybridization (O. sativa x O. rufipogon): Origin of Black Rice Gene from Indian Wild Rice

Abstract

Rice (Oryza sativa L.) is a most important staple food grain consumed by more than half of the worlds population. Wild rice (O. rufipogon Griff.) is considered as the immediate ancestral progenitor of cultivated rice O. sativa, evolved through the process of domestication. Most of the cultivated rice produced grains with white pericarp, but can also produce grains with brown, red and black (or purple rice) pericarp. Red rice pericarp accumulates proanthocyanidin whereas black rice contains anthocyanin, both have antioxidant activity and health benefits. Black pericarp is predicted to be regulated by alleles of three genetic loci- Kala1, Kala3, and Kala4. Recombinational and insertional genetic rearrangement in the promoter region of Kala4 is crucial for the development of black pericarp in rice grain. In the present study, we report first time in the breeding history that aromatic black rice lines were developed through interspecific hybridization and introgression in the genetic background of O. sativa cv. Badshabhog, Chenga and Ranjit. Badshabhog and Ranjit is white grain rice but Chenga is red rice category. Common Asian wild rice O. rufipogon is used as donor parent (red grain) and source of black rice gene. Several possible genetic explanations have come up for the creation of black rice pericarp in the progeny lines. Possible reason may be the rearrangement and insertion of LINE1 in the promoter region of Kala4 allele through recombination mechanism leading to ectopic expression of Kala4 gene for the accumulation of anthocyanin and resulted in black rice formation. Other genes and regulatory factors may be induced and become functional to produce black pericarp. Black pericarp colour appeared in F2 populations in the wide crosses (Badshabhog x O. rufipogon and Chenga x O. rufipogon) but not in the cross with (Ranjit x O. rufipogon). Black pericarp trait inherited in F4 and F5 population with segregation phenotypes. This is a first report in the history of rice genetics and pre-breeding research, that black rice has been created through wide crossing and introgression by combining wild rice O. rufipogon in the genetic background of O. sativa. Present experimental evidence provides a new model of black rice origin. Thus, black rice (indica type) of Indian subcontinent originated independently through natural out crossing and artificial selection in the course of domestication.