17. A new spotted leaf mutant in rice
      Kuldeep Singh, D. S. Multani and G. S. Khush
      International Rice Research Institute, P. 0. Box 933, Manila, Philippines

    In order to obtain new mutants for linkage mapping in rice, seeds of IR68 were presoaked for 16 hours and treated with 1.0% EMS solution (prepared in phosphate buffer pH 7.0) for 10.5 hrs at 30°C over a temperature controlled shaker. A spotted leaf mutant was isolated from M2 population. True breeding nature of the mutant was confirmed in M2. The mutant shows rust colored spots which start appearing at maximum tillering stage and continue until maturity. The spots are distributed throughout the leaf blade with maximum concentraion along the midrib (Fig. 1 ). Inheritance of this mutant was studied by crossing it with IR68. The F1 was normal and in an F2 population of 118 plants, 92 were normal and 26 were mutant. These data agree with a 3 normal : 1 mutant ratio. Thus the mutant phenotype is due to a single recessive gene.
    The F1s of this mutant with spl-1, spl-2, spl-3, spl-4, spl-5, spl-6, spl-7 and spl-9 were all normal. As the data of Table 1 show, the F2 populations except that from its cross with spl-5 segregated in a ratio of 9 normal : 7 mutant thereby showing that the mutant is non-allelic to and independent of spl-1, spl-2, spl-3, spl-4, spl-6, spl-7 and spl-9. The F2 population of its cross with spl-5 did not fit to 9:7 ratio (c2 =16.6) thereby indicating linkage of this mutant with spl-5 which is located on chromosome 7. Allele tests of the mutant with spl-8 and spl-10 could not be carried out due to non-availability of seeds of these mutants. However, spl-8 is located on chromosome 5 (lwata et al. 1978) and spl-10 is located on chromosome 10 (Ideta et al. 1993). Thus, the new mutant is also different from spl-8 and spl-10 and is designated as spl-ll.

Table 1. Segregation of spl-ll with other spl mutants.
 

Cross Total Normal spl c2 (9:7)
spl-ll/spl-I 114 64 50 0.0005
spl-ll/spi-2 III 70 41 2.093
spl-ll/spl-3 120 77 43 3.056
spl-4/spl-ll 74 48 26 2.231
spl-ll/spl-5 119 89 30 16.620**
spl-6/spl-ll 111 69 42 111
spl-ll/spl-7 120 72 48 0.690
spl-ll/spl-9 130 84 46 3.696
**Significant at 1.0% level of significance.
Fig. 1. Leaf of spl-11 mutant.

References

Ideta, O., A. Yoshimura, T. Matsumoto, H. Tsunematsu, H. Sato and N. Iwata, 1993. Integration of conventional
        and RFLP linkage maps in rice, II. Chromosomes 6, 9, 10 and 11. RGN 10: 87-89.
Iwata, N., T. Omura and H. Satoh, 1978. Linkage studies in rice (Oryza sativa L.) on some mutants for
        physiological leaf spots. J. Fac. Agr. Kyushu Univ. 22: 243-251.