Advances in two-line hybrid rice breeding

摘要

The discovery of environment-sensitive genic male sterility in rice led to the development of a simpler and more efficient two-line hybrid breeding system compared with the cytoplasmic male sterility or three-line system. Several elite photoperiod-sensitive (PGMS) and thermosensitive genic male sterile (TGMS) lines have been developed in China. The commercial two-line hybrids developed using these lines occupied about 330,000 ha in 1996. Multiplying PGMS and TGMS lines in a pure form requires some special handling. These methods have been developed in China. Similar methods of seed production have been adopted for both two-line and three-line hybrids.The key point is to determine the time when a PGMS or TGMS line will show complete sterility for about 1 mo at a given location. Seed yield of two-line hybrids in China is 2.25-3.0 t ha -1. Under tropical conditions, in which daylength differences are marginal, the TGMS system is considered to be more useful than the PGMS system.Genetic analysis at IRRI confirmed the monogenic recessive control of the TGMS trait. The TGMS gene of the IRRI mutant, lR32364 TGMS, was found to be nonallelic to the TGMS genes identified in China (tms1) and Japan (tms2). IRRI has developed some TGMS lines in indica rice that possess the tms2 gene; these lines are being evaluated in national agricultural systems. As expected, the TGMS system gave a higher frequency of heterotic hybrids than the CMS system. This chapter also discusses constraints and the future outlook for two-line hybrid rice breeding.