Abstract
To map earliness gene(s) on the 7 th chromosome of rice, Oryza sativa L., three earlyheading isogenic lines T65 ?? R-1, T65 ?? R-5 and T65 ?? R-6, were bred after 9 or 10 backcrosses with Taichung 65 (a cultivar from Taiwan) to two interchange homozygotes T3-7 and RT7-11, and a linkage tester HO 775, respectively. Each early-heading isogenic line carried a dominant earliness gene. The earliness gene was one of the allele of Ef1 locus (early flowering), which is identical with or isoallelic to Ef1b. Ef1 was linked with seven breakpoints involving the 7 th chromosome, 7-11, 6-7, 3-7, 7-8b, 7-9, 7-8a, and 2-7a, and two genes an the chromasome, fgl (faded green leaves) and pgl (pale green leaves), recombination values being 2. 2, 3. O, 7. 8, 11. g, 23. 3, 25. 9, 28. 5, 15. 3 and 29.0%, respectively. Ef1 was estimated not to be located on the 9 th chromosome, but on the 7th, and the early observation of a linkage between Ef1b and the lazy growthhabit gene la on the 9th chromosome was not correct. The arrangement of four linked genes and seven breakpoints on the 7 th chromosome were estimated as pgl-7-8 b-Rf1-fgl-7-11-Ef1-6-7-3-7-7-9-7-8 a-2-7 a.
