The genic identification of dwarfness was conducted by crossings between different dwarf lines. The equivalence of the dwarf gene loci was shown as follows; d8=d11=d14 and dl5=dl6(d10). Non-allelic relations were recognized in 60 combinations of dwarf genes. In addition, unknown genotypes of ten dwarf lines were determined by test crossings. Further, a mutant line induced by gamma-irradiation was governed by d42 which belongs to the second linkage group. Twenty one kinds of near-isogenic lines were produced in successive backcrossings by using the leading variety in Hokkaido, Shiokari, as a recurrent parent. It was shown that the dwarf gehes insert their effects, to various characters and then, the traits of the 21 near-isogenic lines were compared with those of Shiokari. A trial classification was made depending on the distribution patterns of the elongated internodes allotting 21 dwarf near-isogenic lines to nine groups. Pleiotropic actions of the dwarf genes were prominient in grain and seedling characters. These dwarf genes were classified into 13 groups depending on grain length, grain width, grain shape index (length/width) and grain size index (length×width). Increment of grain length or width was recognized in several dwarf lines which belong to the semi-dwarf, while short round grains were produced in some lines which indicated the specific internode pattern. Thus, it is important in rice genetics and breeding to elucidate the genic pathway on morphogenesis and to estimate the genetic composition for the ideal plant type in the breeding of lodging resistance and high yielding capacity.
The relationships between known three linkage groups, the sixth, the ninth, and the twelfth, and chromosomes in rice (Oryza sativa L.)were reexamined by using isogenic lines of Taichung 65 with marker genes and translocation stocks. The marker genes, ghl (gold hull) and d1 (daikoku-type dwarf) included in the sixth linkage group, nl1 (neck leaf) in the ninth, and gl1 (glabrous) in the twelfth group were all found to be located on the second chromosome. Linkabae order of these marker genes and seven interchange breakpoints on this chromosome was established as gh1-d1-2-3-2-3c-nl1-2-6a-2-7a-2-3b-2-lOa-2-3d-gl1 Consequently, two more linkabae groups remain to be established.
In order to get information of low seed set generally observed in sweet potato breeding, first of all, some observations on the normal process of fertilization and embryogenesis were made on the specimens collected at different intervals after pollinations from the compatible cross combination (Chikei 682-ll×Kyushu No.58). Approximately 4 hours after pollination, the pollen tube enters into one of the synergids through the micropyle. From 6 to 9 hours after pollination the double fertilizations occur, bringing forth the zygote and the endosperm nucleus. 14 and 10 hours after pollination both the former and the latter begin to show their first mitotic divisions, respectively. Approximately 24 hours after pollination, the zygote is to be differentiated into an apical cell and basal one, and the several endosperm nuclei begin to lie in the peripheral layer of the embryo-sac. 48 hours after pollination, the zygote is to be developed. into the embryo and the suspensor consisting of 8 cells, with the endosperm nuclei lying densely in the peripheral layer of the embryo-sac. 3 to 7 days after pollination, the zygote is to be differentiated into the embryo ball and the suspensor, and the formation of the cell walls surrounding respective endosperm nuclei begins from the micropyle side towards the antipodal one. 10 days after pollination, the zygote reachs heart stage, and the endosperm cells begin to be degenerated at the micropyle side. 13 to 17 days after pollination, a rapid elongation comes to be shown by the cotyledon, with the endosperm cells almost degen-erated.
An anther culture technique was employed in Citrus aurantiuln L.; 'Sour Orange', 'Bouquet', and two varieties grown in Japan, 'Kabusu (Shu-to)' and 'Choshu-to'. Anthers collected from immature flower buds were cultured on the MURASHIGE and SKOOG's (19692) medium supplemented with or without indole-3-acetic acid (IAA) and kinetin at 28°C in darkness. Embryoid formation vvas generally evident 14 weeks after inoculation of anthers of 'Sour Orange' and 'Choshu-to'. Anthers containing pollen grains at the late uninucleate stage formed embryoids effectively on media with 0.02mg/l of kinetin. Nuclear divisions of pollen grains and multinucleate pollen grains were observed in the 'Sour Orange' an-thers, while embryoids from pollen grains were not observed microscopically so far. After the incubation in light with a 16-hour photoperiod, some of these embryoids differentiated into shoots, developing into plantlets, while some of the other embryoids produced more embryoids mainly from the hypocotyl region. Induction of roots and shoots was stimulated by transfer from the embryoid induction media containing growth regulators to a medium eliminated growth regulators. Root tip cells of some of the differentiated plantlets had the diploid chromosome number.
Karyotype analysis and comparison of chromosome size in four Oryza species, O.sativa, O.perennis, O.punctata and O.officinalis, possessing three different genomes separately, were carried out. As a standard, chromosomes in late prophase, prometaphase and early metaphase cells of O.sativa were analysed. Stages were discrirninated with chromosome length and then the relative length and the arm ratio were measured in three stages. It appeared that the order of chromosome length and the position of centromeres were much the same in all stages, though the staining pattern changed as the stage advanced. In each stage, however, individual chromosomes constantly showed their own staining pattern. Therefore, chromosome identification could be done easily. Karyotypes of other three species were much the same as O.sativa. Characteristics in relative length, arm ratio and staining pattern of twelve chromosome pairs were very similar among four species. In addition, no difference was detected in chromosome size among four species, that is, the absolute length and the ratio of width to length were almost constant in a given stage of these species. So, we concluded that the chromosomes of four species had not been much differentiated morphologically each other.
Aiming to screen mutant genes on nine chromosomes of homoeologous groups, I, V and VII in common wheat (Triticum aestivum L.), selfed seeds of their monosomics and a normal disomic line of cv. Chinese Spring were treated with 0.3 and 0.4% ethyl methanesulphonate(EMS). Higher survival was observed in mono-1A, 1B and 1D than in other monosomics and the normal line in the M1 generation, indicating some increase of tolerance to EMS by the hemizygous state of either the 1A, 1B, or 1D chromosome. A few M2 Iines were bred true for weak chlorosis and necrosis(mono-1A, 1B, 1D, 5A, 5B, 7A, 7D), seedling lethality (mon0-1B, 1D), striped leaf color (mono-1B), dwarfing (mono-1A, 1B, 1D, 5D), or for compactoid (mono-5A) and sphaerococcoid characters (mono-7B, 7D). According to the scheme shown in Fig.1, most of these mutations were assumed to have occurred on a chromosome that was monosomic in the M1 generation. Unique consequences of the mutagen treatment of monosomics, compared to that of disomics, in the M1 and M2 generations are pointed out.
For efficient screening of micro-mutations, it is an important problem to grasp the frequency and the direction of mutations exactly. In this paper, different statistical criteria were compared to estimate the frequency of the grain-size mutations induced by EI treatment (O.5%, 23.5°C, 2 hours) on three rice varieties; Arborio with large grain, Century Patna with slim grain and Amonoquilli with short grain. Increase of variances for the length and the breadth of grain in M2 Suggested the induction of micro-mutations. Mean values in M3 for both the characters tended to shift in minus direction. When aberrants are determined as the plants which fall outside the variation range of the control, the frequency of the aberrants for the length of grain was higher than that for the breadth. And the majority of the aberrants were for minus direction. Similar results were obtained from the stadardizing method which describes the theoretical frequency distribution curves.
To study the relationship between the origin and phylogenetic differentiation of the tetraploid wheats and their susceptibility to leaf rust, a model experiment has been carried out. Namely, using 8 species which had played an important role on the origin and evolution of the genus Triticum, the seedling reactions of them to 2 races of Puccinia recondita Rob. ex Desm. f.sp, tritici were examined. In the consequence of the test, Tritcium monococcum belonging to the Einkorn. group, l strain of T. dicoccoides belonging to the Emmer group, T. araraticum and T. tinoheevi belonging to the Timopheevi group and 2 strains of T. spelta belonging to the Dinkel group were resistant, T. aegilopoides belonging to the Einkorn group, 1 strain of T. durum belonging to the Emmer group, 1 strain of T. spelta and T. araraticum were susceptible, and 2 strains of T. dicoccoides and 2 strains of T. durumshowed various types of responses to avilulent race 1 B. On the other hand, T. monococcum and T. timopheevi were resistant, 2 strains of T. durum and 1 strain of T. spelta showed several types of reactions, respectively, but other wheat strains were sesceptible to virulent race 21 B .Three wild species except T. aegilopoides showed different reactions to 2 races. Namely they were susceptible to race 21 B in all cases, change of the reactions was observed. As a whole, the tendency to show unstable responses to avirulent race 1 B, but stable ones to virulent race 21 B was recognized.
By using the Giemsa C-banding technique, chromosomes in the root meristematic cells of barley (Hordeum vulgare L., cultivar Ehimehadaka No.1, 2n=14) were stained. The C-bands, which reveal the presence of constitutive heterochromatins, mostly localized on the proximal regions of the chromosomes. By the differences in morphology and C-banding pattern among chromosomes, all seven pairs of homologous chromosomes in the same cell could be identified. Furthermore, the chromosomes were divided into two groups. Three pairs (chromosomes 3, 4 and 7) had thick bands and the other four pairs (chromosomes 1, 2, 5 and 6) had thin bands. By using these characteristics of the chromosomes, the behavior of chromosomes during mitotic cycle was investigated. In the early prophase, all chromosomes had 'V' shape and their vertices, i. e. centromeres, were gathered to one pole of nucleus and arms were streched towards the opposite pole. This observation suggests that the chromosomes do not move randomly in the interphase nucleus after the telophase of preceding mitotic division. This interpretation is supported by the finding that the chromocenters, which are corresponded to C-bands on chromosomes, were distributed on one side of the surface of interphase nucleus.
Present examination was performed in order to make clear inheritance of abscission layer and also easily shedding character based on the cracking abscission layer. The strength required to detach rice grain from its pedicel was measured with an unbonded strain gauge transducer and a null balancing recorder. Also, morphology of the abscission region in longitudinal sections of the pedicel was investigated. Parents used were a most easily-shedding variety of Japonica-Indica hybrid, Yushin, and a persistent veriety of Japanese paddy rice, Akibare. The former has abscission layer and parenchymatous cells presented in the abscission layer have completely collapsed at harvest time, and the latter has no abscission layer. In the F1 plants, degree of grain shedding was similar to that of Yushin and parenchymatous cells presented in the abscission layer have completely collapsed. Therefore, it is concluded that the easily-shedding character of Yushin is dominant.