| Heading date (growth duration) is one of the important agronomic traits of rice, and it determines rice adaptation of planting region and season. Utilization of dominant earliness genes can not only enlarge the genetic difference of two parents, but also transform many excellent late-maturing hybrid combinations into early-maturing and high-yielding combinations rapidly. It is generally suggested that earliness is controlled by major recessive genes and/or minor polygenes in rice. Nevertheless, a few of dominant earliness genes have been reported. Tsai firstly identified dominant earliness gene Ef-1 in japonica varieties. Ef-1 gene was located at chromosome 10 of rice and could generally advance rice to head about 10 days earlier. Sato et al. identified dominant earliness gene Ef-x located at chromosome 2 in japonica varieties. The earliness effect of Ef-x gene itself was smaller and sensitive to temperature. But the combined effect of Ef-x and Ef-1 increased extremely and was insensitive to temperature. Deng et al. firstly found out the dominant earliness gene Ef-cd in Indica . Efcd gene was mapped on the short arm of rice chromosome 3, 6.7cM from the microsatellite marker RM231. Through continuous backcross, self-pollination and molecular marker assisted selection, individual Ef-cd gene was isolated and its nearly isogenic lines (NILs) were constructed. In this study, the above nearly isogenic lines were researched in order to validate the nearly isogenic lines harboring Ef-cd, analyze its earliness effect and its effect on the other main agronomic traits, evaluate the application potential in breeding for early-maturity hybrid rice. The results were as follow:1. Validation of the nearly isogenic lines. From segregation of heading date in the F2 population of the nearly isogenic lines crossed with the recurrent parents i. e. MH63, SH881, SH527 and inheritance segregation of microsatellite marker RM231, the nearly isogenic lines were testified. Theresult showed that the segregation ratio of early to late heading plants in the F2 populations fitted the ratio of 3:1 and there was co-segregation relationship between SSR pattern of RM231 and earliness of individual plant.2. Analysis of earliness effect of Ef-cdgene. These nearly isogenic lines and their original recurrent parents, i. e. MH63, SH881, SH527, were planted in Wenjiang, respectively. The results suggested that heading dates of the nearly isogenic lines were 15<sup>18d earlier than that of their original parents. On the other hand, statistical analysis suggested that there was not significant difference between reduction of heading dates of the nearly isogenic lines under long-day and short-day conditions, which indicated that Ef-cd gene was a photoperiod-insensitive dominant earliness gene.3. In Wenjiang, the agronomic traits of the nearly isogenic lines, original recurrent parents and their hybrid combinations crossed with the sterile lines, were investigated, which included heading date, plant height, panicles per plant, spike length, flag leaf length, flag leaf width, grain number per panicle, the number of fertile seed, setting rate and 1000-grain weight. The differences of heading date, plant height, flag leaf length and width between the nearly isogenic lines and recurrent parents were significant at 0. 01 level. And the differences of heading date, plant height, flag leaf length , flag leaf width, the number of fertile seed and setting rate between their hybrid combinations were significant at 0.01 level. The heading date of the combinations that E527-5-5 crossed with G46A, G201A, G203A was 15 days earlier than that of the combinations that SH527 crossed with the same sterile lines and "ShanYou63" , but their yield was lower. The yield of the combinations that E527-5-5 crossed with G46A, G201A, G203A was 5.1%, 5.4%, 6.6% higher than that of "ShanYou77" , and there was significant differences at 0. 01 level. So, it was considered that Efcd gene had important role in rapid developing early-maturing, super high-yielding rice varieties. |
