Trisomic Analysis of a Lateness Gene ef2 in Rice, Oryza sativa L.

Abstract

The lateness gene ef2(t), formerly designated as lf-1, was induced by X-ray irradiation applied to a rice variety Taichung 65. The present study was performed to investigate the allelic relationship between ef2(t) and two earliness genes, Efx and Ef1, and the chromosomal location through trisomic analysis. Rice line T65-ef2(t) carrying gene ef2(t) was crossed with two tester lines, T65-ER-21 and T65-ER-1 harboring the earliness genes, Efx and Ef1, respectively and heading time in the F₂ plants was examined. F₂ plants of the cross T65-ef2(t)/T65-ER-21 showed a trimodal distribution: T65-ER-21 and T65 type, new type and T65-ef2(t) type. The F₂ segregation fitted to a 12: 3: 1 expected ratio. On the other hand, the F₂ plants of the cross T65-ef2(t)/T65-ER-1 exhibited a tetramodal distribution: T65-ER-1 type, T65 type, new type and T65-ef2(t) type, the segregation fitting to a 9: 3: 3: 1 expected ratio. These results suggested that ef2(t) was non-allelic to both Efx and Ef1. Trisomic analysis was performed using seven Triplo lines carrying extra chromosomes 2, 4, 5, 7, 9, 10 and 12, respectively. The trisomics were used as maternal parent for crossing with T65-ef2(t). Heading time in the F₂ plants obtained from self-pollination of F₁ plants (trisomics) was examined. F₂ population derived from a cross between T65-ef2(t) and Triplo 9 showed a typical trisomic segregation pattern, suggesting that ef2(t) was located on chromosome 9.