The species of the genus Oryza and transfer of useful genes from wild species into cultivated rice, O. saliva

The genus Oryza has 24 species out of which two are cultivated (O. saliva and O. glaberrima) and 22 are wild species. Of the 22 wild species, six are in the primary gene pool of O. saliva complex and these wild species are easily crossable with the major cultivated species. These have the same AA genome as O. saliva. However, there are 10 wild species under O. officinalis complex having BB, CC, BBCC, CCDD, EE and FF genomes. The wild species of this complex are in the secondary gene pool and are cross incompatible with O. saliva. There are six most distantly related wild species with either diploids or tetraploids of GG, HHJJ and HHKK genomes and are highly cross incompatible with O. saliva. All the 22 wild species of Oryza are a vast reservoir of genes for biotic and abiotic stresses resistance. Some of the yield enhancing traits/genes from AA genome wild species have been identified and mapped with molecular markers for their integration into O. saliva genome. A broad-spectrum resistance gene for bacterial blight resistance (Xa21) has been identified in O. longistaminata and introduced into many rice cultivars. Advances in biotechnology have facilitated the development of interspecific hybrids between O. saliva and wild species of secondary and tertiary gene pools. Some important genes Pi40 and Bph18 for resistance to blast and brown planthopper, respectively, have been successfully transferred into elite cultivars from O. australiensis and the function of one blast resistance gene (Pi9) derived from O. minuta is elucidated. Many important genes from the most distantly related wild species such as O. alta, O. granulata, O. longiglumis and O. coarctata are expected to be transferred into cultivated rice in the future using the latest tools of molecular genetics and biotechnology.