The more knowledge about heterotic loci is a pre-requisite for enhancing grain yield potential in distant crosses

Overcoming reproductive barrier is one of key indicators for exploiting heterosis in distant crosses. This paper reports the current studies on the genes/QTLs controlling hybrid sterility as well as the heterosis in distant crosses. To avoid hybrid sterility problem in distant crosses of rice, the use of wide compatibility gene and development of partial hybrid rice were adopted consecutively. Though these efforts made, rice scientists were still concerned about hybrid sterility occurrence, which hamper the exploitation of strong grain yield heterosis in rice. But a better understanding of the genetic factors that govern hybrid sterility and heterosis could facilitate the introgression of useful genes/QTLs in rice. In this review, 57 inter-subspecific genes/QTLs and 18 interspecific genes/QTLs were reported to cause hybrid sterility in distant crosses. On other hand, a total of 33 stable Heterotic loci (HLs) were also found to be associated with yield-related traits. The cross-check observation showed 11 genes/QTLs to be implicated in distant hybrid sterility irrespective of the crosses made. Surprisingly, the marker RM236 was identified to be closed simultaneously to the chromosome region affecting hybrid sterility and heterosis. However, many other stable heterotic loci with positive effect on yield-related traits were isolated in rice. Therefore, we propose the pyramiding of these heterotic loci (HL) via marker assisted selection (MAS) into one adaptable rice variety as an efficient approach to develop new rice variety with higher grain yield potential.