Marker assisted transfer of S5 gene to develop universal restorer with wide-compatibility for realization of inter-subspecific heterosis by overcoming indica × japonica hybrid sterility in rice

A major phenomenon hindering development of inter-subspecific rice hybrids is the ‘hybrid sterility’ observed in indica × japonica (IJ) crosses. We had successfully transferred wide compatibility gene S5 in to an elite restorer background for the first time through marker-aided backcross breeding (MABB), and developed wide compatible restorers (WCR) that are genetically diversifiable with japonica for use with indica CMS lines to realize inter-subspecific heterosis. WCR lines also improved the fertility of IJ hybrids by overcoming incompatibility compared to control hybrids. These restorers constitute excellent genetic resources for indica-japonica hybrid breeding. These lines exhibited agronomic superiority over original restorer in terms of earliness, longer panicle, more number of filled grains and single plant yield. MABB for major fertility restoring genes Rf3 and Rf4, background genotyping with genome-wide simple sequence repeat (SSR) markers and stringent phenotyping resulted in superior recipient genome recovery. Thus, the present study opened up the development of a new class of ‘wide compatible restorer’ (WCR) with universal application in hybrid rice breeding such as genetic diversification with japonica, development of restorers with broad genetic base, use of diversified restorers with well adapted indica gene pool towards development of IJ hybrids with preferred grain qualities and high yield.