Four diploid cultivars of sweet oranges (Citrus sinensis (L.) Obseck) were crossed with four tetraploid cultivars and the ploidy levels of the mature embryos from the fully developed seeds were analyzed immediately after germination. Seed set was affected primarily by the seed parents. The mean percentage of fully developed seeds was 55.6, 32.5, 14.0 and 13.1% in “Mediterranean Sweet”, “Kanton orange”, “Joppa”and “Fukuhara orange”, respectively. The germinative embryos from the seeds of “Mediterranean Sweet”and “Kanton orange”consisted of tetraploids and diploids, but those from the seeds of “Joppa”and “Fukuhara orange”were all diploids. The proportions of the seeds wlth tetraploid embryos among fully developed seeds were more or less constant when crosses were made using different pollen parents, the average being 80.5% in “Medlterranean Sweet”and 69.8% in “Kanton orange”. The germinative diploid embryos were also contained in 57.1 and 67.1% seeds with tetraploid embryos from “Mediterranean Sweet”ana “Kanton orange”, respectively.

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The in vitro adventitious bud technique was used in conjunction with gamma irradiation for the induction of mutation in red pepper. The twelve-day-old seedlings were irradiated by gamma radiation at the exposure doses of 0, 0.5, 0.75, 1.0 and 1.25krad delivered at the dose rate of 5krad/h. After irradiation adventitious shoots were induced from the excised cotyledons. The shoots were rooted and the obtained plantlets were grown under greenhouse conditions until maturity. No variant segregation was observed in control plants from both seeds and non-irradiated cotyleclon explants whereas visible variants were found among the M₁ plants regenerated from irradiated cotyledon explants at the frequency of 4.4%. The variation spectrum was consisted of plant type, leaf, flower and fruit variation. Rate of chimerism based on visual characters was considerably high, indicating the multicellular origin of adventitious shoot. A number of variants were recovered in the immediate gamma ray treated generation (M₁). Most of the variant characters obtained were transmitted to the M₂ progeny and were considered as mutants. Some of the characters were bred true and many were segregated. Most of the mutated characters were stabilized in the M₃ generation. Three types of the variant pheonotypes were lost and the causes were discussed.

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B chromosomes (Bs) were detected in a diploid guineagrass (2n=16) strain derived from seeds collected in Tanzania. The number of Bs was constant at the metaphase I (MI) of pollen mother cells in the same plant, and the size of the B in the bivalents and univalents was approximately the same as that of the normal (A) chromosomes at MI. The Bs did not pair with the A chromosomes, but frequently paired with one another when two or more were present. Although the Bs were transmitted through both male and female gametes, male gametes transmitted twice the number of Bs received through microspores after meiosis. Bs had no significant effect on the length of the panicle and leaf, but plant height was decreased by these chromosomes. Pollen and seed fertility was severely depressed in plants having more than three Bs.

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Protoplasts of a normal fertile tobacco variety, Tsukuba 1, were fused with X-irradiated protoplasts of a male sterile (MS) tobacco line, MS Burley 21. Regenerated plants which resembled Tsukuba 1 but showed male sterility were selected, and backcrossed to Tsukuba 1, as the male parent. In the BC₁ generation, 31 MS Iines were examined in a field experiment both for their agronomic characters and the presence of male sterility, and two lines with a better performance were selected. These lines again were evaluated in the three subsequent backcross generations. Male sterility was transmitted throughout these four generations and plants showing male fertility were not observed. The selected lines were not significantly different from Tsukuba 1 in their agronomic characters, and were considered to be comparable to Tsukuba 1 in all the generations. It was concluded that the male sterile lines developed by protoplast fusion were genetically stable even in later backcross generations and therefore could be used for practical breeding of F₁ hybrids in tobacco.

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Simple and efficient procedure of protoplast culture was developed in lettuce. For protoplast isolation, cotyledons from aseptically grown 7 to 10 days old seedlings of lettuce cv. Kaiser were sliced into ca. 1mm strips, and incubated in 0.04% Macerozyme R-10, 0.2% Meicelase, containing O.029M sucrose, 0.5M mannitol and l/2 inorganic salts and vitamins of MS except NH₄NO₃ (200mg/l), for 16h at 25°C without shaking. Protoplasts liberated with gentle shaking by hand were passed through nylon mesh (50μm), and washed three times with 0.5M mannitol containing CPW salts or the modified MS used for enzyme treatment. Isolated protoplasts were cultured at a density of 2.5×l0⁴/ml in the medium with 1/2 inorganic salts and vitamins of MS except NH₄NO₃ (80mg/l), 5mM sodium succinate, 0.5g/l casamino acid. 0.3mg/l BA, 0.3M sucrose, 0.3% Gelrite and an auxin (2, 4-D or NAA) under dim light (ca. 100lux) at 25°C. Colonies were transferred to the liquid medium with the same composition except sucrose (O.15M) after 7 to 10 days, and onto the Gelrite-solidified medium with the same composition as the initial culture medium except sucrose (0.088M) after further 7 to 10 days. Calli larger than 1mm in diameter were transferred onto MS agar medium with BA to induce shoots. Additions of Gelrite to the initial culture medium gave a rapid colony growth, and efficient shoot regeneration. Frequency of shoot regeneration was more influenced by auxin of initial culture medium than by cytokinin of the shoot regeneration medium. The shoots were obtained most frequently when the initial culture medium contained 1mg/l NAA. Shoot primordia differentiated at an early stage of colony growth. By selecting the calli differentiating green shoot primordia, most of calli regenerated plants on the MS agar medium with 0.3mg/l BA. The frequency of calli with green shoot primordia was also influenced by the density of calli in a plate. The higher the density of calli, the lower the frequency of shoot regeneration. Shoot regenerated from isolated protoplasts within 2 months. Only three changes of media were enough to regenerate shoots. The number of colonies was ca. 300per 7.5×10⁴ protoplasts cultured, and most of the colonies regenerated plants. Protoplasts of 7 cultivars of lettuce and 1 of endive were cultured using this procedure, and regenerated plants were obtained from all the cultivars of lettuce and endive.

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Chilling requirement, i.e. the minimum duration of the chilling treatment necessary for full vernalization, of a wheat cultivar should be evaluated by using a measurement which involves not only the growth after the treatment but also the growth during the treatment. Based on this concept, two assumptions were proposed in this study for the growth during the chilling treatment. Subsequently an index “Dof” and a plant-development model using the Dof (Fig.2) were developed on the basis of the assumptions. Through a series of experiments involving 15 wheat cultivars, the accuracy of the assumptions was verified, and the development model was found to be quite adequate for the evaluation of the chilling requirement and narrow-sense earliness. The fifteen wheat cultivars examined in the present experiments were classified into two groups, i. e. spring and winter wheat cultivars by the pattern of flag-leaf unfolding in the absence of chilling treatment. This classification revealed a distinct difference in the chilling requirements between the two groups, and enabled to conclude that the wheat cultivars which required maximum of 30 days of chilling and those which required 40 or more days can be designated as spring wheat cultivars and winter wheat cultivars, respectively. Among the spring wheat cultivars, three that had the Vrn 1 gene and two having the Vrn 3 gene required a chilling treatment of 0 and 30 days for full vernalization, respectively. This finding indicates that Vrn 1 makes wheat completely insensitive to the chilling treatment and that the chilling requirement controlled by Vrn 3 disappears by 30 days of chilling treatment. The experimental results showed that the chilling requirement precisely reflects the demand of a wheat culcivar for low temperature for reproductive growth. Therefore, it is suggested that the chilling requirement is the supremely important trait for understanding the nature and genetics of vernalization.

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In order to reveal genetic variation of the exogenous GA₃ Induced α-amylase isozymes, and to locate the concerning genes on the specific chromosome arm and to analyze the genetic system, this electrophoretic investigation was carried out using seeds of wheat. From comparison of the α-amylase zymograms between the intact and embryo-attached half germinating seeds, it became evident in the half-seed that six additional isozyme bands (10-a, 10-c, 10-d, 10-f, 10-g and 10-i) occurred between bands 9 and 11, which the intact seed and the half-seed had in common, and that all the bands, especially those specified by the genes on the group 6 chromosomes, appeared and disappeared earlier in the germination process than in the intact seed. The substantially same zymogram as that of the embryo-attached half-seed was confirmed in the embryoless half seed treated with GA₃. The six additional bands appeared on the zymogram at 24 hours after treatment with 10^-8M GA₃, and at 15 hours in the case of 10^-6M GA₃. These additional bands occurred also in the whole seed having a slight cut on its endosperm. The investigation including nulli-tetrasomic compensation lines and ditelosomic lines of Chinese Spring wheat proved that the genes for bands 10-c and 10-i were located on the long arm of chromosome 7A (7AL), those for 10-f and 10-g on 7BL and those for 10-a and 10-d on 7DL, respectively. In addition, some unknown element(s) controlling bands 13', 14 and 15 was suggested. Based on variation of those bands that occurred between bands 9 and 11, 21 strains of Dinkel wheat were classified into three types, 30 strains of Emmer wheat were also classified into three types. Timopheevi wheat (four strains) and Einkorn wheat (two strains) showed no variation and the latter had its own specific bands. Gene analysis was carried out with the results that suggested allelism of bands 10-g and 14, and linkage between the genes for bands 10-a and 11.

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A selection method for the resistant mutant to black spot disease was developed in Japanese pear by using the host-specific toxin, AK-toxin I. To determine the conditions of selection for the mutants, Chojuro as the reslstant cultivar, Nijisseiki as the susceptible cultivar and γ-1-1 as the mutant with intermediate resistance were used. Leaf disks from the 1 st to 10 th leaves on these shoots were treated with O.O1, O.1 and 1 ppm of the toxin solution. The combination of 4 th leaf with a concentration of O.1 ppm of the toxin solution was adopted as the condition of selection among the combinations of leaf positions and concentrations of the toxin because the mutant with an intermediate resistance could be consistently identified from the original Nijisseiki. The selection method established was as follows : 1) 5 ml of a O.1 ppm toxin solution was placed on two filter papers in 9cm petri dishes. 2) The 4 th leaf from the top on the shoots was marked with a number. 3) Leaf disks were cut from the 4 th leaf, and 25 leaf disks were arranged on the petri dishes in the field. Then, 1 ml of a O.1 ppm toxin solution was added again. 4) The severity of the symptoms was evaluated after keeping the disks at 25°C for 2 days. It was possible for one person to screen about 500 shoots/day by using this selection method. Actually 2 resistant mutants were selected among 2439 shoots that sprouted after cutting back the chronically irradiated trees of the susceptible cv, Nijisseiki with gamma rays. The mutation frequency was 1.3×10^-3 for a dose rate of 12 R/day and 1.6×10^-3 for a dose rate of 18R/day. The induced mutants exhrbited the same type of intermediate resistance to the disease as that observed in the γ-1-1 mutant.

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[in Japanese]

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[in Japanese]

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Interrelations between leaf senescence, cytokinin and resistance to the green rice leafhopper (Nephotettix cincticeps UHLER) were examined. Cut leaves were prepared by cutting the base of the leaf sheath of the seedlings. The resistance level of the cut leaves which was considerably lower than that of intact seedlings became even lower with the progression of senescence. However the resistance of the cut leaves was as strong as that of intact seedlings when the cut leaves were cultured in solutions containing cytokinin which prevents leaf senescence. Hence it was concluded that senescence is responsible for the breakdown of the resistance of the cut leaves and that the cytokinin which prevents leaf senescence is involved in the resistance mechanism.

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The following new cultivars of winter crops were registered by the Ministry of Agriculture, Forestry and Fisheries (MAFF) on October 27, 1987. The characteristics as well as breeding procedures are summarized herewith based on the notification of “New Crop Varieties” by MAFF (Winter Crops) issued by the Secretariat of the Agriculture, Forestry and Fisheries Research Council.

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