Pattern of Reduction of Lnternode Lengths and Changes of some other Characters in Short-Culm Mutants in Rice

Short-culm mutants of a rice variety, Norin No. 22, whose general characteristics had earlier been studied by Kawai et al. (I960), were investigated for variations of length and number of stem internodes, seedling height, germinability, and correlated changes among these and other related characters.

The results may be summarized as follows:

(1) Number of internodes significantly increased in 2 and decreased in 11 of the mutants.

(2) Internode length in one or more of the four internodes from the top (internodes 1–4) decreased in 29 mutants. Significant decreases were most frequent in the internode 3 followed by in the internodes 1, 4 and 2. The variation of the internode length (relative to control) was the maximum in the internode 4.

(3) Seven early heading and short-culm mutants formed a particular group in respect of changes in internode number and length. Internode number decreased in six of them and lengths of the internodes 3 and 4, particularly of the latter, were markedly reduced in all of them. Relative share of an internode in culm length was decreased in the internode 4 and increased in the internode 1 in the early heading mutants.

(4) In the shortrculm mutants, excluding the seven early heading ones, mean internode lengths decreased by 2.9, 1.5, 1.1 ana 1.1 cm. showing reduction rates relative to control of 7.8, 7.1, 10.0 and 18.4% respectively for internodes 1 to 4. Relative share of an internode in culm length was generally decreased in the internode 4 and increased in the internode 1, though not to such marked extents as in the early heading mutants.

(5) Short-culm mutants were classified into seven groups and one of the groups was further classified into seven subgroups, depending upon the patterns of the relative reductions of internode lengths (relative to control). The general pattern was the marked and maximum reduction in internode 4, followed by that in the internode 3 and often, accompanied by reductions to different degrees in the internodes 1 and/or 2. Several mutants showed patterns distinctly deviating from the general pattern.

(6) Lengths of internodes were, in general, correlatedly changed in the short-culm mutants. In relations between one internode length on one hand and the remaining ones on the other, the correlations were the highest between any two adjacent internodes and the lowest between any two farthest internodes.

(7) Culm length and panicle length showed the highest positive correlations with lengths of the internodes 3 and 2 respectively.

(8) Seedling height was significantly shorter in 18 of the short-culm mutants. However, the correlation between seedling height and culm length in the short-culm mutants was not statistically significant.

(9) Germination percentage and germination velocity, especially the latter, were frequently reduced in the short-culm mutants and decrease of germination velocity was statistically significant in more than 40 per cent, of the mutants. The reductions were, to a certain extent, associated with the early ear emergence.

All the results have been discussed in comparison with the findings in barley, durum wheat and rice reported by other workers.