Reproductive barrier between the two cultivated species of rice

Oryza glaberrima Steud., the African cultivated species of rice, was long recognized as an important source of agronomically important traits for O. sativa L. breeding (Bocco et al 2012; Ndjiondjop et al 2012). However its utilization has been constantly hampered by the strong reproductive isolation between the two cultivated rice species (Sano et al., 1979). The main factor for this sterility barrier was identified as the S1 gene by Sano (1990). With IRD (France), we initiated a study that aimed to obtain a high-resolution mapping of the S1 gene on chromosome 6, using four interspecific BC1F1 O. sativa x O. glaberrima populations and looking at allelic frequencies on chromosome 6 for SSR and R-BIP markers. This resulted in the mapping of S1 in a 28 kb region, and the identification of two tightly-linked genes acting in epistasis with S1. A genetic model for gametic elimination in the F1 hybrid was developed, and inference on patterns of sequence divergence between the two species were made (Garavito et al 2010; Guyot et al 2011).