The information about heredity which defines every living species is packed in its genome. The discovery of DNA as the material of inheritance and subsequent elucidation of its double helical structure laid the foundation for comprehensive genome analysis, which aims at gaining all the genetic information or sequence of nucleotides of major organisms. Extensive analysis of the rice genome which was initiated in 1991 in Japan has resulted in the production of a large amount of important data with a considerable impact on traditional rice and cereal genetics. This has led to a new direction of rice research and has provided biologists with powerful research tools to reveal the function of all the genes that comprise the rice genome. The new knowledge generated from this endeavor will be very useful for developing novel strategies for rice breeding that will ensure a stable food supply for mankind.

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A simple and rapid colorimetric method for the selection of individual rapeseed plants with low glucosinolate contents was developed using one of a pair of germinated cotyledons of a single seedling and a glucose-measuring method employed in clinical tests (CII-Test method). The CII-Test method can be used to estimate the amount of glucose released by the hydrolysis of glucosinolates extracted from a germinated cotyledon. In the present experiment, HPLC analysis showed that the total glucosinolate content of germinated cotyledons was not significantly different from that of seeds three days after seed sowing. When the glucosinolate content of the seeds and/or cotyledons was estimated by the glucose-measuring CII-Test method and HPLC method, high positive correlations were recognized between both types of measurements. The CII-Test method exhibits some clear advantages in that 1) the glucosinolate content can be estimated in an individual plant, and 2) 150–500 samples can be estimated by one person in one day. These advantages indicate that the glucose measuring CII-Test method is suitable for efficient and accurate selection of rapeseed plants with low glucosinolate contents in the F₂ generation.

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Inter-simple sequence repeat (ISSR) amplification was evaluated for its usefulness in generating DNA markers for sweetpotato and related wild species. ISSR markers were obtained through PCR amplification using simple sequence repeat (SSR) primers. Optimization of the reaction conditions was successfully achieved for 24 % out of 100 SSR primers screened. The functional primers included anchored and unanchored primers. All of the anchored primers used were dinucleotide repeat motifs. The unanchored primers consisted of tri-, tetra- and penta-nucleotide repeat motifs. Eight primers were selected and employed to assess the genetic diversity and relationship between 34 accessions of sweetpotato and its related wild species. The ISSR markers are highly polymorphic among the taxa studied. Several sweetpotato accessions were clustered together based on their geographic origin. The mode of inheritance of the ISSR markers was analyzed in a pseudo-test cross mapping population. Twenty-two SSR primers amplified 70 reproducible polymorphic ISSR markers and Mendelian segregation of polymorphic bands was demonstrated. Among the 70 ISSR markers, simplex and duplex markers accounted for 70 % and 15.7 %, respectively. One linkage between two simplex ISSR markers was found. Thus, the ISSR markers could be suitable for fingerprinting of cultivated sweeptotato and its related wild species and for constructing a linkage map of sweetpotato.

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Using yield data collected in the preceding steps of selection (historical information) for the evaluation of the yielding ability of test varieties is essential to increase the efficiency of stepwise yield screening of plant varieties. Selection in each step should be performed based on the average score over the preceding and current steps. Three methods of weighting can be used to calculate the average score, i.e., inverse variance (IV), field area (FA) and equal (EQ) weighting. In IV, yield data collected in the preceding and current steps are weighted by the inverse of the error variance of the corresponding steps, while those in FA are weighted by the field area (or plot numbers) allocated per variety. A simple average score is used in EQ. Of these three methods, although IV is the best theoretically, it has not been recommended previously nor is commonly used in actual screening trials because two necessary statistics, i.e., variances due to the measurement error (V) and variety × year interaction (I), may not be estimated correctly. Our studies demonstrated that the superiority of IV to the other methods persists under possible degrees of inaccuracy in the estimates of V and I. Calculation of the inverse-variance-weighted average does not require significant extra resources or expensive facilities. We therefore suggest that method IV be used with the necessary statistics V and I being estimated from the yield data obtained in the current and earlier steps. Stepwise screening thus performed is superior to non-stepwise screening where the yield of all varieties is measured in the same years and evaluated based on the average over the years.

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NaCl tolerant cell lines were selected from irradiated callus, which were generated from seed cultures. M₁-regenerates were obtained from the salt-tolerant callus cultured on the auxin-free medium for 30 days. Some regenerants were more tolerant than the parent variety (Dongjinbyeo) on a medium containing 0.75 % NaCl. Seeds (M₃ 5,000 lines) derived from M₂ lines were grown to the 3 leaf stage. M₃ lines were soaked with a 0.75 % salt solution for 3 weeks and 350 salt-tolerant genotypes were selected. Among the M₃ 350 lines, forty tolerant lines were selected from a saline field (10~14 mS) near the sea coast. Of the forty lines, two lines (18-1 and 50-1) showed more improved plant height, panicle length, tillering number, spikelet number and yield than those of the original variety. Thirty primers were screened and two RAPD markers were identified, which appeared in both the salt-tolerant lines (18-1 and 50-1). From DNA-hybridization experiments, it appeared that the fragment arose from the middle-repetitive copy sequences. The transcript involved in the marker showed a higher expression in the salt-tolerant lines than the sensitive lines. The salt-tolerant lines would be useful as a resource for salt-tolerant breeding.

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The present study was conducted in order to analyze the effects of the genes for long glume (P), hairy glume (Hg), black glume (Bg), non-glaucousness (W₁^I) and purple culm (Pc) on 18 agronomic characters of durum wheat. Six near-isogenic lines (NILs, 10 backcrosses) and their recurrent parent LD222 were used. The experiment was carried out in the experimental field of the Agricultural University of Athens, Greece, over a period of two years. The NILs for P, W₁^I and Pc differed from LD222 in 14, 7 and 4 traits, respectively. These genes had no effect on plant height but exerted adverse effects on the grain yield traits. The P gene was associated with later heading, increased rachis length and 100-kernel weight, but lower grain yield and yield components. Although the data were not statistically significant, both W₁^I and Pc genes induced a lower grain yield which was accompanied by a reduction of the 100-kernel weight, kernel weight/spike and number of tillers. On the other hand, the introduction of either the Bg or Hg gene into the LD222 genetic background did not affect appreciably the agronomic traits studied.

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A cabbage plant forms a mature head during the continuous process of vegetative growth, suggesting that head formation is affected by developmental characteristics before harvesting. We investigated characteristics of early maturing F₁ hybrid varieties using 27 F₁ hybrids composed of 21 F₁ hybrids of mixed reciprocal combinations of 42 diallel crosses of 7 inbred lines and 6 commercial F₁ hybrids. We estimated the number of days it took for the head to attain the target weight from transplantation (head-maturing period, HMP). The HMP to reach 1250 g (HMP1250), the most marketable weight in Japan, varied from 60 to 88 days among the materials and corresponded to their estimates based on grower’s experience. We thus considered that the HMP1250 was a valid measure of cabbage maturity. Correlation analysis between HMP1250 and developmental characteristics clarified that HMP1250 was correlated with the leaf shape index (width/length) of wrapper leaves, the leaf position at which head formation started and the size of wrapper leaves. This result suggested that cabbage maturity could be divided into those developmental characteristics. That is to say, early maturing F₁ hybrid varieties had the following developmental characteristics; change to a large leaf shape index from the low leaf position, low leaf position at which their head formation started and large leaf size.

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A genetic linkage map of soybean was constructed by using a cross between a cultivar ‘Keburi’ and a weedy form of soybean ‘Masshokutou Kou 502’. The parents differed in their ability in somatic embryogenesis. The mapping population consisted of 117 recombinant inbred lines (F₁₁), and generated 30 linkage groups, which covered 2089 cM, including 515 amplified-fragment-length polymorphism (AFLP) markers and 85 simple sequence repeat (SSR) markers. For AFLP analysis, a simple technique using small polyacrylamide gels combined with silver staining was applied, which enabled a single person to construct a map in a short time at a reasonable cost. Comparison of this map with previously published maps revealed that 1) the level of polymorphism was the same as in a cultivar × cultivar cross; and 2) the cultivar × weed map was 13 % shorter than the cultivar × wild map. The high-density map constructed in this study would contribute to the molecular mapping of quantitatively and qualitatively inherited characters from weedy forms of soybean.

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To clarify the inter- and intraspecific variations of floral traits in rice, we investigated eleven traits related to pistil, stamen and glume using 128 Asian cultivated rice (Oryza sativa L.) accessions including 72 Indica and 56 Japonica type accessions, and 53 wild rice (O. rufipogon Griff.) accessions including 32 perennial and 21 annual ecotype accessions. We examined the results from three specific levels: intraspecific variation between perennial and annual ecotypes of wild rice, interspecific variation between cultivated rice and wild rice, and intraspecific variation between Indica and Japonica type cultivars. The annual wild rice accessions exhibited a shorter stigma and anther than the perennial wild rice ones. The cultivated rice accessions showed a lower stigma exsertion, shorter stigma, shorter anther, and thicker and wider lemma and palea than the wild rice accessions. These floral traits of cultivated rice are considered to play an important role in selfing and high seed production. None of the floral traits showed distinct differences between the Indica and Japonica type accessions in cultivated rice, although the Indica type accessions tended to display a slenderer stigma and glume than the Japonica type accessions. It is suggested that the varietal differentiation into the Indica and Japonica types is not likely to be related to genetic variations of floral traits. We clarified the differences in floral traits between annual and perennial ecotypes of wild rice, between cultivated rice and wild rice, and between the Indica and Japonica type cultivars, and discussed the relationship between genetic variations of floral traits and domestication and varietal differentiation in rice.

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The existence of a sorghum (Sorghum bicolor Moench) thermo-sensitivity gene has been proposed to account for the acceleration of flower initiation when plants are exposed to a temperature lower than 20°C. Four varieties and their F₁, F₂, F₃ and BC₁F₁ populations were evaluated for days to emergence of flag leaf (DEFL) under the field condition of a long daylength (> 13 h) and temperatures over 20°C for at least 40 days after sowing. The F₁ hybrids, Hiromidori (Norin Ko-2) : 390 (early) × Regs.Hegari (late) and Natsuibuki (Norin Ko-9) : MS175 (late) × Daikoukaku (early), showed the same flowering response as Regs.Hegari and MS175 which show a delay in DEFL under temperatures over 20°C, suggesting the presence of a dominant thermo-sensitivity gene. In two different F₂ populations, the segregation of early and late plants for DEFL fitted in with the expected ratio of 1 : 3, indicating that a single dominant gene was controlling the phenotype. The inheritance mode was confirmed in two different BC₁F₁ populations, where the expected ratio of 1 : 1 (early : late) was observed in the segregation of BC₁F ₁ of 390 × F₁ and F₁ × Daikoukaku. As expected, no segregation was observed in BC₁F₁ populations of F₁ × Regs.Hegari and MS175 × F₁. These results suggest that the sorghum thermo-sensitivity for flower initiation is controlled by a monogenic dominant gene of late over early, and the symbol TT is assigned to the genotype in which flower initiation is accelerated by the exposure to a temperature lower than 20°C.

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We introduced a modified delta-endotoxin gene, modified cry1Ab (mcbt) of Bacillus thuringiensis, which displays a specific biological activity against lepidopteran insects into chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura]. The chrysanthemum cultivar ‘Shuho-no-chikara’ was transformed using a disarmed strain of Agrobacterium tumefaciens, EHA101, carrying a binary vector, pIG121mcbt that harboured a mcbt gene encoding an insecticidal crystal protein (ICP) fragment of B. thuringiensis var. kurstaki HD-1. Leaf discs were co-cultured with Agrobacterium and thereafter cultured on the callus induction medium containing G418. A total of 317 shoots were regenerated from 3,618 leaf discs on the regeneration medium (8.8 %). The mcbt gene was detected in all the regenerated plantlets by Southern blot analysis. The accumulation of Cry1Ab ICP in 20 transformed lines, selected at random, was confirmed by Western blot analysis. The level of accumulation of Cry1Ab ICP ranged from 10.5 ng to 80 ng per 50 μg total soluble protein (from 0.021 to 0.16 % of the total protein). Insect bioassay was conducted using tobacco budworm (Helicoverpa armigera) larvae and all the larvae of H. armigera tested died during the first instar on the leaves of the mcbt-transformed lines whose expression level of Cry1Ab ICP exceeded 47.6 ng per 50 μg compared to the wild type cry1Ab-transformed lines. Significantly higher feeding inhibition and/or growth inhibition of the insects was observed, compared to those on the non-transformed control plants.

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