Bacterial grain rot of rice, caused by Pseudomonas glu-mae, was detected in Fukuoka Prefecture in 1955. Area of infected paddy fields has increased since the 1970's. At present the disease has become one of the most serious rice diseases in the southwestern Japan. But no resistant culti-vars have been found. The purpose of the present study was to make varietal differences in resistance to bacterial grain rot clear by establishing new methods of inoculation and evaluation. Seventy five Japanese and 54 foreign rice cultivars in total were used for the experiments in paddy fields of Saga University in 1987 and 1988. Three panicles per plant were inoculated with 0.2 ml of the inoculum per panicle using a syringe at booting stage. The inoculum was adjusted to a concentration of approximately l07cfu/ml . Two weeks after inoculation the disease development was evaluated using two different disease scores, the panicle disease score and spikelet disease score. The correlation coefficient between the two disease scores in 1988 was 0.847. Variances of years, cultivars and interaction be-tween two years were all significant at the I O/o level. The correlation coefficient between the spikelet disease scores of 1987 and 1988 was 0.474 which was significant at the I olo level. These results indicate that degree of resistance to Pseudomonas glumae can be evaluated by the new screening methods, even though environmental conditions influence severity of the disease.

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Two trials were conducted to determine the effect of IB/1R chromosome translocation on selected agronomic characteristics of spring bread wheats(Triticum aestivum L.)developed at the International Maize and Wheat Improvement Center(CIMMYT). Five bread wheat genotypes with a chromosome IB/1R translocation and five without representing a sample of high yielding germplasm were identified for the experiment. NonIimiting levels of fertility and moisture with a preventive pest and disease program were used. Plant height, days to heading, grain yield, aboveground biomass at maturity, harvest index, yield components and test weights were determined. Genotypes with the IB/1R chromosome translocation had 2.2% higher aboveground biomass yield, 2.1 Vo more spikes m², 1.12 g higher 1, 000-grain weight and 0.8 kg/ha¹ higher test weight. The non-1B/1R genotypes had 0.8% higher harvest index and 0.6 cm longer spikes. Cultivar comparisons indicated that the IB/1R group headed 2.5 days later than the IB group.

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Mechanism and inheritance of resistance to rice stripe virus (RSV) in several varieties were studied. It was apparent that Musashikogane and Minamihatamochi were highly resistant and IR 50 and TN I were moderately resistant to virus infection. IR 50 was found to be resistant to the small brown planthopper (SBPH) which was the vector of RSV. The inheritance of resistances to RSV and SBPH were studied by using the F3 and F6 generations of a cross of IR 50 with a susceptible variety, Reimei. The distribution of RSV and SBPH resistances at F3 and F6 were continuous and suggested a pluralgenes control of resistance. The F3 and F6 Iines were classified into groups of resistant (R), moderately resistant (M) and susceptible (S) to RSV infection and the SBPH resistance level of each group was evaluated. No significant difference was observed between the R and M+S groups of F3, however, the R group of F6 was significantly more resistant than the M and S groups. Thus an influence of SBPH resistance on the RSV infection of F6 was suspected. It was estimated that SBPH resistance was effective in reducing RSV infection, and the RSV resistance in IR 50 based on the resistances to SBPH and virus infection and they were controlled by pluralgenes.

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In the regenerated plants by the anther culture of rice, panicle length, plant height and glume length were measured. Only the glume length was able to separate regenerated plants into three distinct classes.The cytological analysis of these plants revealed that the three classes based on the glume length consisted of haploids, diploids and triploids, respectively. Similar results were obtained in the regenerated plants derived from irradiated callus. With irradiation as a physiological disorder, the glume length was a stable index of the ploidy level of rice plants.

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We previously proposed a new breeding scheme to develop hybrid wheat utilizing male sterility induced by the interaction between the S^vtype cytoplasm of Ae. kotschyi and the IBL-1RS chromosome (Toriyama et al. 1991, 1993). In our proposed scheme male sterility-maintainer lines can be produced by two ways, i. e. the backcrossing method (Nonaka et al. 1993) and anther culture. This article reports the results of anther culture. Donor for the 1BL-1RS chromosome, namely, the strain 911-B-8-10 (abbreviation, st. 911) was crossed to 13 Japanese wheat cultivars. The anther culture was conducted using the F₁ and B₁F₁ plants. Frequency of embryo formation in the Fls was higher than that in the parental Japanese cultivars. The frequency observed in the B₁F₁s was lower than that in the F₁s. High frequencies of embryo formation in st. 911 and the Fls were attributable in part to the 1BL-1RS chromosome. Since the leaf rust resistance gene Lr 26 was located on the 1RS chromosome arm, regenerated haploid seedlings were artificially inoculated by leaf rust (race 21B) to select resistant ones. Doubled haploids with resistance were crossed with (S^v)-Chinese Spring having the IB chromosome and with (S^v)-Salmon having the 1BL-1RS chromosome. The F₁s of the former cross showed high selfed fertility, while the Fls of the latter showed complete male sterility. This means that resistant doubled haploids obtained by anther culture can be used as a maintainer for developing male-sterile line.

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Induction of desiccation tolerance by abscisic acid (ABA) and osmotic stress was investigated in microspore-derived embryos of Chinese cabbage. Exogenous application of ABA was effective for germination and plant regeneration from dry embryos whose water content decreased to approximately 10% by transfer to a series of desiccators in which the relative humidity remained constant. Induction of desiccation tolerance depended on the ABA concentration, but not on the genotype. The maximum percentages of germination (87.60%) and plant regeneration (46.30%) were obtained in the embryos treated with 10_μ ABA. Though osmotic stress by high concentration of sorbitol also induced desiccation tolerance, its effectiveness was less appreciable than that of ABA. On the other hand, all the embryos lost their viability after desiccation, when they were not treated with ABA or exposed to osmotic stress. The dry embryos treated with ABA were able to regenerate into plants in soil. Protein analysis revealed that ABA and osmotic stress increased the accumulation of seed storage proteins in microspore-derived embryos.

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Mesophyll protoplasts of sweet potato, variety Chugoku No.25, were isolated from shoot tip cultures grown in vitro. After the surface of the leaves was scratched with sterilized carbo-rundum, they were plasmolyzed for I hour in 0.3 M sorbitol and 0.05 M C_aCl₂. The enzyme solution for isolation contained 0.1%Pectolyase Y-23, 2 % Cellulase Onozuka RS, 5 mM C_aCl₂ and 0.5 M mannitol in a modified K3 medium (Kao and Michayluk 1981). The crude protoplast suspension was filtered through a nylon mesh and protoplasts were isolated by discontinuous density gradient centrifugation. The initial medium used was a modified KM8p medium (Kao and Michayluk 1975) sup-plemented with 0.1 mg/l zeatin (ZEA), 0.1 mg/1 2, 4-dichlorophenoxyacetic acid (2, 4-D). 0.5 M mannitol and 10 g/l sucrose. The cell colonies formed were plated on a mQdified MS medium (Murashige and Skoog 1962) for callus forma-tion containing 20 g/l sucrose, 2 g/l Gellan Gum, 0.5 mg/l 2, 4-D and I mg/1 abscisic acid (ABA) with or without 0.5 mg/l kinetin (KlN) or 0.5 mg/l ZEA. Furthermore, the calli were transferred to a MS medium for regeneration supplemented with 30 g/l sucrose, 2 g/l Gellan Gum and 1 mg/l KlN or 0.5 mg/l ZEA. Compact calli were induced on the medium supplemented with ZEA, and regenerated plants were obtained. The effects of silver nitrate (AgNO₃) and drying on plant regeneration were investigated. AgNO₃ was not effective for plant regeneration, but the drying treatment for 3 days prior to transfer to the medium for regeneration was effective. Cell suspension protoplasts were isolated from the embryogenic calli initiated from the shoot apical domes in the same manner as used for mesophyll protoplast isolation. The initial culture medium and the callus proliferation medium were identical to those used for mesophyll protoplast. Drying treatuent was also effective to enhance the frequency of adventitious bud formation, and regenerated plants were obtained.

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The association between high-molecular weight (HMW) subunit alleles of glutenin and agronomic traits was examined in 52 doubled haploid (DH) Iines produced from an F1 hybrid (Chinese Spring x Norin 61) of bread wheat by the bulbosum technique. In addition, the effect of gibberellin (GA)-insensitive semi-dwarfing alleles involved in these DH Iines was assessed. The identified alleles coding for the HMW subunits of glutenin were Glu-Alc and Glu-Dla in Chinese Spring and Glu-Alb and Glu-Dlf in Norin 61. The DH Iines were grouped into the four genotypes recombinated at the two HMW subunit loci. No significant difference was found in grain hardness among the genotypes. Only the lines of the recombinant genotype Glu·Alc·Glu·Dlf expressed delayed heading time and taller plant height than those with the other three genotypes. On the other hand, Norin 61 carried the allele Gai/Rht2 for GA-insensitivity whereas Chinese Spring was GA-sensitive. The DH Iines were grouped into two genotypes at the Gai/Rht2 Iocus. The lines of the Gai/Rht2 genotype were significantly shorter in plant height and higher in grain yield than those of the gai/rht2 genotype. The combined effect of Glu-Alc and Glu-Dlf in extending plant height almost nullified the effects of Gai/Rht2 in reducing plant height. These results suggest that the selection for glutenin lici remarkably affects the expression of certain agronomic traits in bread wheat.

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The effects of three antibiotics and culture methods were investigated to find out reliable selection procedure for Agrobacterium -mediated transformation in cucumber (Cucumis sativus L.). When cotyledonary explants without inoculation of Agrobacterium were cultured on agar medium containing kanamycin, geneticin (G 418) or hygromycin, callus formation and greening of explants were suppressed more effectively by G 418 or hygromycin than by kanamycin. However, G 418 and hygromycin could suppress effectively callus formation only at the part of explants contacting with an agar medium. In order to expose the whole surface of explants to antibiotics, tissues were cultured in a liquid medium. Combination of liquid culture and addition of G 418 or hygromycin were highly effective in suppressing callus formation from uninfected explants. Explants infected with Agrobacterium were cultured in a liquid medium with each antibiotic. Hygromycin or G 418 resistant calli were selected under the presence of 20-80 mg/l hygromycin or 20 mg/l G 418, respectively. Calli formed at 20 mg/l hygromycin were transferred to a regeneration medium, and regenerated plants were obtained via embryogenesis. PCR analysis demonstrated integration of hygromycin phosphotransferase (HPT) gene to all regenerated plantlets and transmission of HPT gene to their progeny.

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The genetic mechanism of cool temperature resistance at the booting stage of rice, is largely unknown in spite of the significance in rice cultivation. We have screened 317 M₂ lines derived from chemically mutagenized cv. Taichung 65 which is highly resistant to cool temperature. Repeated screening from M₃ through M₆ generation recovered seven cool temperature sensitive mutants. They showed significantly lower seed fertility than Taichung 65 when treated with cool water (19°C). Although the seed fertility fluctuated to some extent with years, four of the seven mutants showed very low seed fertility and one relatively high but significantly lower seed fertility than Taichung 65 and The remaining two showed intermediate values. Segregation of seed fertility in F2 plants between Taichung 65 and the mutants suggested that many of the mutants were due to single-gene recessive mutations. In four mutants, pollen development was severely damaged by cool water treatment. Also female organ (embryosac) was malformed in some mutants. These seven mutants are potential materials for the investigation of cool resistance in rice.

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The effects of sugars, phytohormones and amino acids were examined on the growth of excised embryos from compatible crosses in 'Oriental' hybrids (Lilium 'Casablanca' ×L. 'Stargazer') and in 'Asiatic' hybrids (L. 'Connecticut King' ×L. 'Capri'), and also from incompatible crosses of L. 'Casablanca' × L. 'Connecticut King' and L. 'Casablanca' ×(L. auratum × L. nobilissimum ). Embryos obtained from the crosses of the 'Oriental' hybrids could grow on the medium containing more than 3 % sucrose, but not on the medium containing 3 % sucrose irrespective of the addition of phytohormones and amino acids. Similary a higher concentration of sugar was necessary to culture the 'Asiatic' hybrid embryos. The optimum sucrose concentration is considered to be 6 %, since most of embryos on media containing 9 % and 12 % sucrose formed abnormal shoots or stopped growing within two or three months of the culture. When sucrose was partially replaced by mannitol, the survival rate was similar or increased. Addition of mannitol is recommended to adjust a high osmotic pressure of medium. Cytokinins and higher concentration of auxins induced abnormal growth of embryos. Amino acids did not affect growth of embryos. The plants from the cross between an 'Oriental' hybrid and an 'Asiatic' hybrid were obtained on the medium with high osmotic pressure, and these were confirmed to be hybrids by leaf morphology, isozyme analysis and chromosome observation.

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We identified a novel mutant line lacking an α-subunit. The line was obtained by subjecting to gamma-ray irradiation Kari-kei 434, a genetically fixed line with a low level of β-conglycinin which is characterized by the absence of the α '-subunit and low levels of both the α -and β-subunits of β -conglycinin, one of the major soybean storage pro-teins. The mutant line which lacks both the α - and α '-subunits went through two generations without displaying any physiological abnormalities. We concluded that the induced trait characterized by the lack of the α -subunit is truly inherited.

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[in Japanese]

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Viviparous mutants were obtained among M₂ progenies of rice cultivars, Nihonmasari, Norin 8 and Koshihikari after EMS, gamma ray or thermal neutron mutagenesis. Frequencies of germinated seeds on panicles in these mutants ranged from 9.94 to 23.56 % in 1990 and from 4.43 to 24.88 % in 1991. Single recessive genes were assumed in all the mutants based on the analysis of genetic segregation of viviparous mutants in their progenies.

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Cell division of isolated immature pollen grains was induced by sugar starvation in rice cv. Nipponbare. Irmuature pollen grains were isolated from a freshly harvested panicle without any pretreatuent. The pollen suspension was fractionated based on the size (37-50μm in diameter) and density (lighter than 35 % Percoll solution) of the grains. The fraction was incubated in a sugar-free medium consisting of R2 salts with various concentrations of KH₂PO₄ instead of NaH₂PO4, B5 vitamins and 0.5 mg/l 2, 4-D (pH 5.8). After sugar starvation, a sucrose solution was added to a final concentration of 5 InM. Sugar starvation was essential to induce cell division of the pollen grains and the optimum period of sugar starvation was three days. The optimum concentration of KH₂PO₄ in the medium was 1 mM for induction of cell division. It was shown that sugar starvation for three days in the medium containing I mM KH₂PO₄ resulted in the highest frequency of colony fornration at 0.04%. Out of 200 calli, three produced green plants while 15 produced albino plants.

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Asymmetric somatic hybrid calli of birdsfoot trefoil and rice were produced by protoplast fusion, and analyzed for their mitochondrial DNAs (mtDNAs) and chloroplast DNAS (CpDNAS) by the method of Southern hybridization. Novel mtDNA fragments were detected in one hybrid callus line, indicating that some kinds of mtDNA alterations occurred in the hybrid calli. On the other hand, the cpDNA fragment patterns of all the hybrid callus lines were found to be identical with those of birdsfoot trefoil. Therefore, it is suggested that the cpDNAs of these hybrid calli were segregated unidirectionally. Interestingly, some regenerated plants from the hybrid calli were tolerant to low temperatures and low sunlight intensity.

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[in Japanese]

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[in Japanese]

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