X. Wu.’, K. TAKEDA2 and H. Kitano1

     A mutant DMF-l induced from the rice cultivar Fujiminori by X-ray irradiation ultimately shows semidwarfism with fairly normal growth except for the reduced 2nd internode length (Yamaguchi 1976, Wu et a!. 1997). The authors previously reported that the dm-type character of this mutant was controlled by an incomplete dominant gene Ssil located on chromosome 1 (Wu et a!. 1997). We also reported that the newly identified dm-type dwarf mutants DMT-7 and DMT-1 1, which were induced from the rice cultivar Taichung 65 by N-methyl-N-nitrosourea treatments, were controlled by multiple alleles, d6l-l and d61-2, at the same locus on chromosome 1 (Wu et a!. 1999). DMT-7 and DMT- 11 were distinguished from each other by their peculiar internode elongation patterns, dm-type and pseudo-d6-type, respectively.

     The linkage relationship between Ssii and d6l remains unclear because oniy one marker gene shri (shrunken endosperm 1) linked to both gene loci has been found. We conducted a linkage analysis to clear the relationship between these gene loci. In order to identify the chromosomal location of Ssil, a marker line Fl-576 carrying r14 (rolled leaf 4) on chromosome 1 was crossed with DMF-1. For the mapping of d61 by using Ssil as a marker gene, DMT-1 1 was crossed with DMF-1.

     The F2 population of Fl-576 x DMF- 1 was classified into four distinct phenotypes (Table 1). The ratio did not fit to the 9:3:3:1 ratio, showing the linkage relationship between r14 and Ssil. The recombination value was estimated to be 10.4%. The F2 population of DMT-1 1 x DMF-l involved only three phenotypes, i.e., DMF-1 type, DMT11 type including double mutant type, and normal type (Table 2). The ratio did not fit to the 9:4:3 ratio, suggesting the linkage relationship between SsiI and d61-2. The recombination value was estimated to be 23.8%. Our previous results on linkage analysis revealed that both Ssil and d61 were linked to shri with recombination values of 10.1% and 2 1.7%, respectively (Wu eta!. 1997, 1999). Using these results and the genetic distance between r14 and shri on the conventional linkage map (Kinoshita 1995), we mapped the Ssil and d61 loci on chromosome 1 (Fig. 1). 

Table 2.  Linkage Analysis between Ssi1 and d61