イネ

The present authors have long engaged in the studies on auto-triploid plants with the purpose of establishing the primary trisomic set in rice. It is well-known that triploids produce the primary trisomics in their progenies of selfing or crossing with diploids. With above purpose, cytological observations on the triploids were attempted and self and reciprocal cross pollinations between the triploids and diploids were made. And further, the observations on development of hybrid seeds were conducted. The results were reported in this paper. The auto-triploid plants used in these studies were produced previously from the crossing between auto-tetraploid and its original diploid plants, introducing the embryo-culture technique. 1) Cytological observation on auto-triploid plants At first metaphase 5 to 12 trivalents and 0 to 7 univalents per cell were found. On the average, its meiotic configuration was 10.38 III + 1. 58 II + 1.67 I in first metaphase and 11.09 III + 0.89 II + 0.97 I in diakinesis. In some configurations univalents were more formed than trivalents, that was the cases of 11 III + 3 I, 10 III + 1 II + 4 I, 9 III + 2 II + 5 I and 8 III + 3 II + 6 I in first metaphase, and 11 III + 3 I and 10 III + 1 II + 4 I in diakinesis. These configurations showed that a set of three homologous chromosomes did not pare with each other, but formed three univalents separately. The frequencies of above configurations were 2.6％ in first metaphase and 2.8% in diakinesis on the average. In subsequent meiosis, several lagging chromosomes were found. They varied from 0 to 6 per cell at first anaphase and 0 to 4 at second anaphase. Average was calculated at 0.63 per cell in first anaphase and 0.18 in second anaphase. 2) Crossing results and seed development When triploids were selfed or crossed by pollen grains of diploid plant, many imperfect seeds which developed very poorly and contained no endosperm were obtained. They were formed at the rate of about 20% to pollinated flowers in both of the self and cross pollinations. Their weights and germinating abilities were very light and low, but rather higher in cross pollinated seeds showing 4.0 mg and 2.5% of weight and germinating rate respectively than selfed ones which could not germinate and were 1.3 mg of weight. Besides the imperfect seeds, a small amount of perfect seeds was formed. They were plump and well-developed externally and well-germinated. The seed setting ratio in cross and self pollinations was 3.6 and 0.4% respectively. When diploids were pollinated by pollen grains of triploid plant, seed fertility was very low, that was 0.7% of imperfect seeds and 1. 6％ of perfect seeds. In order to make clear the development of F1 seeds, imperfect seeds of 3X×2X and 3X selfing and perfect seeds of 3X×2X were fixed separately at the matured stage that was about 30 days after pollination, and provided for embryological observation. Embryos of 3X×2X were as large as normal embryo of control, and almost all of the embryos differentiated 3rd foliage leaf as control. But some irreguralities were found, i.e. 18 embryos ovserved lacked the 3rd foliage leaf and radicle, and shape of all embryos ovserved was more or less irregular. Embryos of imperfect seeds of 3X×2X were rather larger than normal embryo, but differentiation was rather retarded. The third foliage leaf had differentiated only in 15.8% of the materials used and in 21.1% stopped the growth before differentiation stage. Another embryos stopped the growth at 2nd or 1st foliage leaf stage. Abnormality was also observed in the shape as mass-formation, that was lacking in inner organs, irregular angle between radicle and plumule and irregular direction in the ovule.