New dm-type Dwarf Mutants Varying in Internode Elongation Patterns are Controlled by Different Mutant Genes at the Same Locus in Rice (Oryza sativa L.)

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Four new dm-type dwarf mutants DMT-7, DMT-8, DMT-10-1 and DMT-11 were induced from the rice cultivar Taichung 65 (T65) by treatment with N- methyl-N-nitrosourea. These mutants were characterized by a remarkable reduction of the 2nd internode length. Experimental results on the morphological characterization showed that these mutants could be classified into two different groups, type 1 (DMT-7 and DMT-8) and type 2 (DMT-10-1 and DMT-11). Type 1 mutants developed not only dm-type but also dn-type culms in a plant whereas type 2 mutants showed mostly pseudo-d6-type and rarely dm-type culms in a plant. Gene analysis using F_2 popurations from the crosses of these mutants with T65 demonstrated that the four mutants were controlled by single recessive genes. Allelism tests indicated that all the mutant genes were located at the same locus. Thus, different phenotypes between the two groups were controlled by different alleles at one locus. Moreover, the alleles of type 1 were dominant over those of type 2. However, no remarkable phenotypic differences were observed between the mutants within each group. Hence, gene symbols for DMT-7 (type 1) and DMT-11 (type 2) were designated as d61-1 and d61-2, respectively. The results of linkage analysis using three morphological markers revealed that d61 was linked to shr1 (shrunken endosperm 1) on chromosome 1 with a recombination value of 21.7% .