Abstract:

The hybrid rice (Oryza sativa L.) breeding that was initiated in China in the 1970s led to a great improvement in rice productivity. In general, it increases the grain yield by over 20% to the inbred rice varieties, and now hybrid rice has been widely introduced into Africa, Southern Asia and America. These hybrid varieties are generated through either three-line hybrid and two-line hybrid systems; the former is derived from cytoplasmic male sterility (CMS) and the latter derived from genic male sterility (GMS). There are three major types of CMS (HL, BT and WA) and two types of GMS (photoperiod-sensitive (PGMS) and temperature-sensitive (TGMS)). The BT- and HL-type CMS genes are characterized as orf79 and orfH79, which are chimeric toxic genes derived from mitochondrial rearrangement. Rf3 for CMS-WA is located on chromosome 1, while Rf1, Rf4, Rf5 and Rf6 correspond to CMS-BT, CMS-WA and CMS-HL, located on chromosome 10. The Rf1 gene for BT-CMS has been cloned recently, and encodes a mitochondria-targeted PPR protein. PGMS is thought to be controlled by two recessive loci on chromosomes 7 and 12, whereas nine recessive alleles have been identified for TGMS and mapped on different chromosomes. Attention is still urgently needed to resolve the molecular complexity of male sterility to assist rice breeding.

Key words: hybrid rice, male sterility, Oryza sativa.