| Results and Discussion Table 1 indicates that 'Ai-bian 1' has very short stature and leaf length, but has normal number of tillers, spike length and number of floret in comparison with other two. All three variety has 4.2 internodes in average. This indicates that the dwarfness of 'Ai- bian 1' is due to short internode length but not to the reduction of internode number. 'Ai- bian 1' has relatively small stamens (2 mm in length) and it flowers without completion of head emergence. The pollen fertility and seed-set of 'Ai-bian 1' are normal except that the late tillers tend to have less seed-set. The 33 F1 plants examined showed almost similar height to each other and the F2 family segregated into short and tall with 3:1 ratio, suggesting that the dwarfism of 'Ai-bian 1' is controlled by a single dominant gene (Fig. 1, Table 2). Chi-square test, carried out on each F2 monosomic group, showed that all groups except one in 4D group fit to 3:1 ratio for the gene action of a single dominance (Table 2). On the other hand, 4D group had significant different segregation from 3:1 ratio, and, also, had the least standard deviation and mean height among F2 monosomic groups (Fig. 2, Table 2). 4D group had only one tall plant (55 cm) , which might be nullisomic because it had narrow leaves, less tiller number and low fertility. These results indicate that the dwarf gene of 'Ai-bian 1' locates on chromosome 4D. Except 4D group, the 530 F2 monosomic progeny were examined, and the culm length frequency had two peaks at 40-44 cm and 65-69 cm, so that F2 monosomic progeny could be classified into two groups if divided at 50 cm. This segregation gives a good fit to 3:1 ratio with Chis-square test. This result indicates, also, that 'Ai-bian 1' had a single domonant gene of dwarfism. The distribution of plant hight in F2 family of 1A showed a different shape from others (Fig. 2), where the peak was at the shortest column (20-24 cm) and the frequency tended to down along the height went up (Fig. 2). The plant height of 5D group was the highest with the largest standard deviation among the F2 groups. MORRIS et al. (1972) reported the similar phenomena in the monosomic analysis with 'Tom Thumb" to the present observations. One of the semi-dwaf genes in 'Norin 10' Rht-2 was reported to locate on chromosome 4D (GALE et al. 1975), where the dwarf gene of 'Ai-bian 1' was involved in. However, the present data indicate the gene action of dwarfism in 'Ai-bian 1' is different from that of Rht-2 in 'Norin 10'. The preliminary observation suggested the dwarfness of 'Ai-bian 1' was insensitive to GA3. The further study will be conducted with sufficient population size on the interactions of this gene with other semi-dwarf genes as well as detail analysis on gibberellin sensitivity. |
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