A.C. SANCHEZ and G.S. KNUSH

International Rice Research Institute, P.O. Box 933, Manila, Philippines

The liguleless mutant stock of rice (Nagao and Takahashi 1963) lacks the auricles, ligule and does not have a visible collar. The mutation was reported to be due to a single recessive gene located on chromosome 4. Sanchez and Khush (1994) reported a recessive gene for purple leaves (pl2) and located it on chromosome 4. We tried to determine the linkage relationship of these two genes by crossing ig (RGS No. 16) and p12 (RGS 298). In an F2 population of 441 plants, we scored for segregation of three characters:

purple leaf (pl2), absence of ligule (Ig), and absence of collar hereby designated as col. Table 1 shows the segregation of the three characters in the F2 population. The p12 was found to be 10.3 map units from ig and 11.8 recombination units from col, while col and ig loci show 4.5% recombination. Thus, the results indicate that the Ig mutant stock is also homozygous for col.

An auricleless mutant (aul) on chromosome 4 was reported by Librojo and Khush (1986). The mutant has no auricles and the ligule is rudimentary. The aul gene is not allelic to 1g. We observed auricleless plants in the F2 population of the cross between p12 and 1g. The ligules of these plants, however, are not rudimentary (Fig. 1) and are normal in size. Unfortunately, the F2 population was not scored for the auricleless character. However, since the auricleless phenotype was observed to segregate from the liguleless and collarless phenotypes, these three loci must be different.

Table 1. Segregation of p12, ig and col in the F2 population