The research progress and prospects of two-line hybrid rice in China

Two-line hybrid rice is new technology for exploiting rice heterosis established based on the discoveries of photo- thermo-sensitive genic male sterile (PTGMS) rice in China. The male fertility alteration of PTGMS line was controlled by recessive nuclear genes in sporophyte and induced by day-length and temperature during young panicle differentiation stage. Compared with three-line hybrid rice technology, it has three advantages: (1) The sterility is controlled by recessive nuclear genes. Any genotype with good combining ability can be used as a male parent. The frequency of obtaining heterotic hybrids in testcrosses is higher than in three-line system. (2) It simplifies the process of hybrid breeding program and shortens the breeding period for rapidly developing new hybrid rice. (3) It provides more kinds of sterile lines for diversifying hybrid rice. More than 300 PTGMS lines and over 900 two-line hybrid rice hybrids were developed and certificated in past three decades, and released in twenty provinces of China. The area covered under two-line hybrid rice was 5.5 million hectares yearly on the average, occupying 35% of total area of hybrid rice planting. Developing PTGMS lines with resistances to multiple-diseases and insect pests, short growth duration and lodging tolerance, exploiting indica-japonica heterosis for increasing yield, and ensuring safe and stable two-line hybrid rice seed production, will be the tasks for further maintaining and expanding two-line hybrid rice in future.