Introgression of major QTLs for increased primary branching and grain number in selected rice varieties by marker-assisted backcrossing

Rice is a staple food for over half of the world's population and therefore plays a very important role in securing the world food supply. The major quantitative trait loci (QTLs) WEALTHY FARMER'S PANICLE (WFP), which controls the number of primary branches per panicle, and grain number 1a (Gn1a), which controls the grain number of rice, have the potential to dramatically increase rice yields. A strategic approach based on marker-assisted backcrossing is being used to introgress these two major QTLs from the rice germplasm stock ST12 into 14 rice cultivars that are preferentially cultivated by farmers in Asia and Africa for their adaptive traits and good grain qualities. Foreground and recombinant selection were performed from BC2F1 when 87.5% of the donor background genome has been recovered. Preliminary results showed that both WFP and Gn1a have positive genetic effects on the target traits even at early backcross generation BC2F2 plants that were derived from NERICA 1 x ST12 cross and that are homozygous for the ST12 WFP allele recorded a 54% higher average number of primary branches per panicle compared to plants that are homozygous for the NERICA-1 WFP allele. This consequently increased the grain number per panicle of plants homozygous for the ST12 WFP allele by 29%. Similarly, plants carrying homozygous ST12 Gn1a allele recorded a 36% increase in grain number compared to those that are homozygous for the NERICA 1 Gn1a allele. No significant differences in the 100-grain weight were observed between plants with homozygous ST12 WFP or NERICA 1 WFP allele, and between plants with homozygous ST12 Gn1a or NERICA 1 Gn1a allele. Similar results were also observed in the early breeding lines derived from the other 13 recipient lines. Efforts are currently underway to pyramid WFP and Gn1a into each of the recipient lines, as well as to fix both traits into each to the recipient genomes.