The semidwarf gene, sd-1, of rice (Oryza sativa L.). I. Linkage with the esterase locus, Estl-2.

The linkage relationship between the semidwarf gene (sd-1) and the isozyme locus EstI-2 was elucidated using segregating populations derived from crosses between several semidwarf testers and tall rice varieties. Bimodal distributions for culm length were observed in F2 populations of three cross combinations, including Shiokari/Shiokari (sd-1), Taichung 65 (A,Pn,Pau)/Taichung 65 (sd-1), and Milyang 23/Kasalath. Taking the valley of the distribution curves as the dividing point, two height classes were apparent with a segregation ratio of 3 tall∶1 short, demonstrating this character to be under the control of a single recessive gene. An inheritance study of esterase isozymes, based on isoelectric focusing (IEF), showed that the EstI-2 locus had two active allozymes of monomeric structure and one null form, which were designated "a", "b", and "n", respectively (Eun et al. 1990). Semidwarf testers such as Shiokari (sd-1), Taichung 65 (sd-1) and Milyang 23 have an active allozyme designated as EstI-2(aa), while the tall parents, Shiokari and Taichung 65 (A,Pn,Pau), have the active allozyme, EstI-2(bb), and Kasalath has a null form of the allozyme, EstI-2(nn). By dividing F2 populations based on EstI-2 allozyme patterns, culmlength distributions exhibited trimodal curves. Most of the short plants had the homozygous EstI-2(aa) pattern of the short parents, most of the tall plants had the homozygous pattern, EstI-2(bb) or EstI-2(nn), and most of the intermediate plants had the heterozygous EstI-2(ab) or EstI-2(an) banding pattern. Einkage analysis indicated that sd-1 and EstI-2 were tightly linked. These findings were also confirmed by segregation analyses in F3 progenies. No recombinants among 171 F3 families from the Shiokari/Shiokari (sd-1) combination, five recombinants among 267 F3 families from Taichung 65 (A,Pn,Pau)/Taichung 65(sd-1), and only two recombinants out of 237 F3 families from Milyang 23/Kasalath, were found. The recombination values were 0, 1.87 and 0.8%, respectively.