Pollen culture of Nicotiana rustica was performed by using 3 tages of pollen as the experimeutal materials. Freshly isolated pollen failed to form embryoid regardless of the presence of NAA and BA. Embryoids were produced from pollen isolated from anthers precultured on agar medium for 4 days or liberated. from anthers floated on liquid medium for 6 days. Prolonged preculture, however, reduced embryoid formation in both methods. Presence of NAA and BA in the media inhibited the induction of embryogenesis even at extremely low concentrations. Chilling pretreatment of flower buds at 5°C for 4 days remarkably increased embryoid formation. The inhibitory effect of prolonged preculture on liquid medium medium was cancelled by the chilling pretreatment, but not the case in the preculture on agar medium. By using the method with preculture on liquid medium, embryoid formation occurred in both uninucleate and mitotic stages but not in the early binucleate stage where high androgenic response, although, was observed in anther culture.

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When exposed to cold-temperature at an early growing stage after seedling emergence. withering rate of F₂ (Milyang 23 × Somewake) population with cytoplasm of a highyielding indica cultivar, Milyang 23, was nearly double as compared to that of F₂ (Somewake×Milyang 23) population with cytoplasm of a japonica cultivar, Somewake, which is one of the most cold-temperature tolerant cultivars in Japan. A similar cytoplasmic effect on the withering rate was observed also between F₂ (Milyang 23×Yoneshiro) and F₂ (Yoneshiro×Milyang 23) populations. Of F₂ populations with the japonica cytoplasm, however, F₂ population with Somewake cytoplasm was more tolerant than that with Yoneshiro cytoplasm. After cold-temperature treatment, survived F₂ plants of reciprocal crosses between Somewake and Milyang 23 showed a similar frequency distribution of leaf chlorophyll content. However, survived F₂ plants of Yoneshiro×Milyang 23 showed less chlorophyll content than F₂ of reciprocal crosses between Somewake and Milyang 23, although there existed no significant difference of chlorophyll content between Somewake and Yoneshiro. F₂ plants showing higher fertility at maturing stage occurred, inversely, much more frequently in F₂ of Milyang 23×Somewake than that of the reciprocal cross.

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Inheritance of the number of ground suckers in tobacco (N. tabacum L.) was investigated by analysis of F₁, F₂ and F₃ plants of two varietal crosses, MC × Virginia 115 and Matsukawa × Odrauma, following MATHER'S additive-dominance genetic model. Dominance genetic variance was larger than additive genetic variance in the cross between MC and Virginia 115, while additive variance was larger than dominance one in the cross between Matsukawa and Odaruma. Since narrow-sense heritability values for F₃ Iine mean were 66.47 and 93.49% respectively, selection for this character is expected to be effective in F₃ and F₄ generations. The number of ground suckers is estimated tb be controlled by three effective genetic factors for the cross bewteen MC and Virginia 115, and by six for the cross between Matsukawa and Odaruma.

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The reciprocal translocation method was employed, for the most part, to conduct linkage studies in rice plants. Thirty reciprocal translocation lines, thirteen marker genes and the C type trisomics were use in this study. A gene for round kernel was identified and designated as rk2. It was found that the marker genes, d1 (linkage group VI), nl1 (IX) and ri (IX) were associated with chromosome 2. Therefore, the results supported the early studies on the integration of the linkage groups VI and IX by the trisomic method. The linkage group III to which eg, spl6' lax and d10 belong corresponded to chromosome 3. It was found that a gene, d18' was located also on chromosome 3. A gene for spotted leaf, spl1' which was found as one of the genes composing a new linkage group by IWATA and OMURA (1975), was located on chromosome 4, and it was also suggested that rl1 and nal2 were located on the same chromosome. The three genes, fl, pgl and rk2, were shown to be located on chromosome 7.

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Rice varieties belonging to five ecotypes, Aus, Aman, Boro, Bulu and Tjereh, and those of Japanese origin were examined for various characters, such as acid phosphatase zymogram, phenol reaction, grain shape, etc. Japanese rice and Bulu ecotype were characterized by an isozyme gene, Acp_l⁹, negative phenol reaction, the length/width ratio of the grain less than 2, slow water absorption in seeds, reduced elongation of mesocotyl after 4h water soaking, short mesocotyl length in a given water content at the time of high-temperature treatment and the small amount of oxygen absorption in a given soaking time. The results suggest that Japanese rice should have close relationship with the Bulu ecotype.

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The crossabilities with tetraploid Hordeum bulbosum L, and haploid producsion by embryo culture in Japanese wheat varieties was investigated. Crossing procedures with high humidity and the application of gibberellic acid after pollination increased seed set, and floret maturity was also favourable for crossability. Seven of the eight Japanese varieties examined were crossable with H, bulbosum at mean frequencies of 4.4%-24.0% seed set. By embryo culture, approximately half of the embryos obtained from the crosses of Japanese varieties with H. bulbosum developed into haploid wheat plants. These results suggest that the doubled haploid method by crossing with H, bulbosum can be promising for wheat breeding programmes in Japan.

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Co-evolution of wheat and rust fungi has been a recent interest of the present authors studying of the origin and phylogenetical differetiation of wild tetraploid wheats. The Botanical Expedition Party of Kyoto University to the Northern Highland of Mesopotamia in 1970 has brought us one sample of durum wheat leaves naturally infected by leaf rust, which was collected at the Agricultural Station of Sulaymaniya of IRAQ. A race, isolated from the leaves and established as a rust fungus (Puccinia recondita Rob. ex Desm., on T. aestivum L, cultivar Norin No. 16), has been identified as race group 1 after testing the seedling resction to Chester's standard differential varieties, and tentatively called "IS-No.1". Preliminary examination of the pathogenicity of IS-No.1 to eight species of Triticum has proved that 1) two Einkorn species were resistant or moderately resistant 2) two Timopheevi species were immune 3) two Dinkel species were resistant or susceptible 4) wild Emmer species were susceptible, but the reactions of cultivated Emmer species were very unstable. These results suggest that IS-No.1 is paticularly pathogenic to the Emmer wheat, so that this race was designated as "Mesopotamia race" affer the collection locality.

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In the previous reports, the author has clarified that unbalanced growth in the floral glumes and caryopsis of rice results in such aberrant grains as notched or hull-cracked grains. Because the grain size of a rice plant is generally conditioned by many minor genes, it should be treated as a quantitatively inherited character. However, if the major genes controlling grain size are available, analysis of their action may offer more simple and precise understanding about the genetic mechanism of grain development. In the present experiment, the effects of minute grain genes on the length of floral glumes and the potential length of caryospsis have been investigated with the nine F₂ populations (Table 1). The potential length of the caryopsis (T1) was estimated by the length of "glume-cllpped grains", upper parts of the floral glumes were clipped-off a few days after the anthesis to allow the development of caryopsis without restriction by the size of floral glumes, while the inner length of floral glumes (C1) was indicated by the length of "non-treated gralns" which naturally developed in a state encased in the floral glumes. Without exception, T1 was longer than C1, and the T1/C1 ratio varied from ca. 1.O to larger than 1.7 in the 1, 483 F₂ plants examined.

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Growing plants of bread wheat (Triticum aestivum L. 2 n=6x=42, AABBDD) were subjected to acute or chronic irradiation by gamma-rays from 60Co and meiotic chromosome behaviours of PMCS in M₁ generation were cytologically compared. Both acute and chronic irradiations produced different types of chromosomal aberrations at the meiotic stages. Among them, translocation type was the most frecluent, followed by univalent type. A mixed type, i. e. translocation accompanying one or more univalents was often detected. Even normal type which lacked translocation and univalent included laggards and briclges without exception. Other meiotic abnormalities such as deletion, iso-chromosome and micronuclei were observed frequently in both treatments. Dose dependency of translocation frequency was not recognized in this experiment. In chronic irradiation, different chromosome numbers and meiotic behaviours were found not only among florets of a spike but also among anthers of a floret. A number of plants with aneuploid-like grass types occurred at a high frecluency in M₁, especially with low exposure.

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The objective of the present investigation was to examine the usefulness of ovule culture for the production of interspecific or intergeneric hybrids which failed in their growth during the development of crossed ovules. The experiments were carried out in the combination of Nicotiana tabacum and N. rustica. In this combination, many attempts to obtain the hybrids had previously been made. The reports showed that the pollen tubes of N. rustica stoped in the styles of N. tabacum and could not enter the ovules, while in the reciprocal cross, almost all of the crossed ovules failed in their development although fertilization took place and only a few hybrids could be obtained. The histological observation of the ovules of N. rustica pollinated by N. tabacum showed that the nucellar hyperplasy in the crossed ovules began 4 days or so after pollination and then almost all of the ovules shrinked and died from about 6 days after pollination(Fig.1). In the 5th day after pollination, the viable embryos at the stage of early globular were observed in the crossed ovules. This observation suggests that the crossed ovules should be excised and transferred to culture medium by the 5th day after pollination.

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Lm alleles that belong to the linkage group I control the photoperiod sensitivity of cultivated rice. The heading responses of Lm alleles to the seasonal change of natural daylength were analyzed. Two isogenic lines with Lme and Lmu alleles were grown through the year in the greenhouse in the Tohoku National Agricultural Experiment Station at 39°29' North Latitude and were examined for their heading time. Lmu/Lmu line headed 59 days after planting, 18 days earlier than Lme/Lme line when they were planted in late December. However, in the ordinary summer culture the earliness of the two lines was reversed with the later heading of Lmu/Lmu line being later than Lme/Lme line (Fig.2). The fall planting after August resulted in the earlier heading of Lmu/Lmu line again. The reverse order of the earliness between Lme/Lme and Lmu/Lmu lines occurred in March and July plantings.

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