Sustaining rice production by tapping hidden genes from wild species for tolerance to biotic and abiotic stresses

A number of biotic and abiotic stresses reduce rice productivity. To enhance sustainability there is thus an urgent need to broaden the gene pool of rice for tolerance to these stresses. Fortunately, wild species of Oryza are an important reservoir of useful genes. The authors use tissue culture and molecular marker technologies to overcome incompatibility barriers (low crossability, increased sterility, hybrid invariability), and in the precise monitoring of alien introgression. Interspecific hybrids have been produced through direct crosses and embryo rescue between elite breeding lines of rice and wild species representing AA, BBCC, CC, CCDD, EE, FF, GG, HHJJ and HHKK genomes. Following embryo rescue and backcrossing, a large number of introgression lines have been generated and alien genes transferred across crossability barriers. Molecular marker analysis revealed limited introgression of small alien chromosome segments from distant genomes of Oryza, while A genome wild species showed frequent introgression from each of the 12 chromosomes. The authors have successfully transferred resistance to bacterial blight from O officinalis (CC) into new plant type rice and from O. brachyntha (FF) into IR56; brown planthopper resistance from O. minuta (BBCC) and O. australiensis (EE) into elite breeding line; tolerance to tungro and acidic soils from O. rufipogon (AA) and IR64. One of the breeding lines derived from the crosses of IR64 x O. rufipogon have been recommended for tungro prone areas of the Philippines as stop gap variety. This variety has become popular in Iloilo province. Another elite line derived from IR64 x O. rifopogon has been released as a variety `AS996' in Vietnam. This, is a short duration variety possessing moderate level of tolerance to acid sulfate conditions and is occupying more than 35,000 ha in Mekong Delta. The alien gene introgressed from wild species showing wide spectrum of resistance to biotic and abiotic stresses demonstrated the usefulness of tapping hidden genes from wild species for sustaining rice productivity