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.)

Four new dm-type dwarf mutants DMT-7, DMT-8, DMT-10-1 and DMT-11 were induc ed from the rice cultivar Taichung 65 (T65) by treatment with N-methyl-N-ni trosourea. These mutants were characterized by a remarkable reduction of th e 2nd internode length. Experimental results on the morphological character ization showed that these mutants could be classified into two different gr oups, type 1 (DMT-7 acid DMT-8) and type 2 (DMT-10-1 and DMT-11). Type 1 mu tants developed not only dm-type hut also dn-type culms in a plant whereas type 2 mutants showed mostly pseudo-d6-type and rarely dm-type culms in a p lant. Gene analysis using F-2 populations from the crosses of these mutants with T65 demonstrated that the four mutants were controlled by single rece ssive genes. Allelism tests indicated that all the mutant genes were locate d at the same locus. Thus, different phenotypes between the two groups were controlled by different alleles at one locus. Moreover, the alleles of typ e 1 were dominant over those of type 2. However, no remarkable phenotypic d ifferences 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 an d d61-2, respectively. The results of linkage analysis using three morpholo gical markers revealed that d61 was linked to shr1 (shrunken endosperm 1) o n chromosome 1 with a recombination value of 21.7%.