Inviability of hybrids, often referred to as hybrid lethality, is a type of reproductive isolation. Hybrid lethality is observed in some plant species, including Nicotiana species, and can be an obstacle when desirable genes are to be introduced into cultivated species by wide hybridization. Wild species in Nicotiana section Suaveolentes (which consists of species restricted to Australasia and Africa) yield inviable hybrids after crosses with the cultivated species N. tabacum. Genetic studies have revealed that hybrid lethality in the cross N. tabacum×N. debneyi is caused by the interaction between gene(s) on the Q chromosome of N. tabacum and a single dominant gene in N. debneyi. Furthermore, programmed cell death with apoptotic features is involved in hybrid lethality. Some factors related to hybrid lethality have been elucidated in the cross N. suaveolens×N. tabacum.

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Plant interspecific F₁ hybrids sometimes are vigorous, but they also reveal sever weakness which has been known as hybrid lethality. Hybrid lethality acts as a major reproductive barrier, eventually blocks gene exchanges between species. Unavailability of interspecific hybrid progenies is an obstacle for widecrossbreeding, and requiring information on nature of hybrid lethality to improve efficiency of this breeding program. However, little is known about physiology and biochemistry of the hybrid cell death, and the genes involved in hybrid lethality are enigma. Recently, new studies started to uncover the facts about how hybrid cells die and which genes are supposed to control hybrid lethality. This article reviews up-to-date studies on hybrid lethality in plants.

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The major storage protein of rice seeds is glutelin, which comprises various subunits. Changes in the subunit composition of glutelin can greatly affect the nutritional quality of rice. Even though our previous studies demonstrated that the subunit composition was changed by altered nitrogen and sulfur metabolism using transgenic plants expressing a sulfur-rich protein and a detached ear culture method, the response of intact plants was unknown. In this report, intact rice plants were analyzed and found to change their subunit composition following high levels of nitrogen fertilization using conventional sandy soil and hydroponic culture systems. The excess nitrogen treatment in the sandy soil culture reduced GluA subunits and increased GluB subunits, which contain more lysine. And thus the excess nitrogen treatment was estimated to increase the lysine content by 7% compared to the standard treatment. The effect of sulfur metabolism on the subunit composition was uncertain in this study. In consequence, the subunit composition modified by the nitrogen metabolism control was crucial for the nutritional quality improvement of the seeds of intact rice plants.

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A paddy rice variety Kinumusume, is a recommended variety in Hyogo prefecture, as it is high quality and has a high palatability. We investigated methods of fertilizer application using split dressing and planting density, and slow release fertilizer for Kinumusume with high palatability, high quality and high yield. Planting density of 15.2 and 21.2 hills per m² produced no difference in yield component, grain yield, protein concentration in rice (less than 7%) or palatability in a sensory test. Topdressing at ear formation stage increased ear length, number of grain per ear, 1,000 grain weight and yield. Topdressing tended to increase protein concentration in rice and decrease palatability, in particular application of 4kgN/10a. Slow release fertilizer produced no difference in growth, yield component or grain yield. Slow release fertilizer with topdressing increased yield but decreased palatability. We estimated that it was possible to cultivate Kinumusume with high palatability, high quality and high yield by basal dressing 4kgN/10a and topdressing at ear formation stage of 2kgN/10a. And we estimated that it was likely to cultivate Kinumusume with quality and high yield by basal dressing from 5kgN/10a to 7kgN/10a using slow release fertilizer.

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Egeria densa, a submerged monocotyledonous plant, is thought to be hopeful for removing eutrophic substances from lake and river. In this study, influences of two environmental factors, water temperature and day length, on the growth and nitrate (one of major eutrophic substances) assimilation were investigated. Two growth parameters, elongation rate and relative growth rate (RGR), were severely inhibited at 17℃. There were interactions between nitrate concentration and day length on the shoot growth of Egeria densa cultured at 25℃. When the plants were cultured with 20 to 2,000μM nitrate, the growth rate and RGR were highest at the concentration of 200μM under continuous and 16h lighting, suggesting the optimal concentration of nitrate for growth. Furthermore, lower nitrate uptake from whole plant of Egeria densa was found under 8h lighting. These results show that Egeria densa has potential for removal of eutrophic substances in warm and long-day environment.

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In a black soybean variety 'Tanba-Guro', We studied to model growth that attained high yield, 250g/m², high 2L ratio, 70%. For examination of 2006-2008, pod per m² was positively correlated with yield (r=0.96^**), relationship of pod per m² and 100 grains weight (R² (Coefficient of determination)=0.82) was strong. And also, percentage of 2L (above 10mm diameter) grains of all grains weight (2L ratio) (R²=0.90), too. Until 370pod/m², numbers of pod did not still regulated 2L ratio. For high yield, for example 250g/m², required 250pod/m². So that pod per m² was positively correlated with number of node of main stem, 17 nodes (contented cotyledon) were required for 250pod/m². In case that numbers of node of main stem were more than 15, 2L ratio was maximum when PNR (pod per m²/number of node of main stem) was about 4.5-7.5. Thus condition to achieve high quality and high yield in black soybean was 250pod/m² (planting density: 2 plant/m², 125pod/plant, PNR=4.5-7.5). And it was important that 17 nodes of main stem were required for the black soybean that has attained both high quality and high yield.

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Seed shattering is important for wild plant species to guarantee efficient seed propagation. In rice, two shattering loci, sh4 and qSH1, with strong effects on seed shattering were previously identified through the map-based approach. In this study, a rice cultivar, Oryza sativa Japonica cv. Nipponbare, and an annual wild accession, O. rufipogon W630 were used as plant materials. The former contains non-functional alleles at sh4 and qSH1, whereas the latter has shattering alleles at both loci. Since the ancient humans selected non-shattering mutants in the past, it is important to evaluate shattering behavior of plants carrying non-functional alleles in the genetic background of wild rice. Therefore, O. sativa cv. Nipponbare was backcrossed twice with O. rufipogon, and backcross plants at BC₂ generation were produced. Among them, the substitution plants having both cultivated alleles at sh4 and qSH1 loci in the genetic background of wild rice were selected by dCAPS and microsatellite markers. Using these lines and the parents, the temporal changes of shattering degree after flowering were examined based on the breaking tensile strength values for detachment of seeds from the pedicels. At 5 days after flowering, the shattering degrees of the substitution lines were almost similar to that of wild accession. They decreased moderately but maintained around half values of cultivated Nipponbare at 10 days after pollination. Probably, partial formation of abscission layers in pedicels might allow matured seeds to be kept on the panicles. These results suggest that the wild rice may still keep additional gene(s) promoting the formation of abscission layer besides qSH1 and sh4 alleles.

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Backcross populations are useful for evaluating the agronomic traits from unadapted germplasms. In this study, we produced 159 and 170 backcross recombinant inbred lines (BRILs) at the BC₂F₈ generation between Oryza sativa Japonica Nipponbare (a recurrent parent) and O. rufipogon W630 and between O. sativa Indica IR36 (a recurrent parent) and O. rufipogon W630, respectively. These BRILs were found to have nearly homozygous genome constitutions based on the marker genotypes at SSR loci covering whole chromosomes. Since their selfed progenies have almost identical genotypes in each line, the simple test tube method was applied for BRILs (BC₂F₉ generation) to evaluate the ability of fast shoot elongation after germination stage under submerged condition. Then, QTL analysis of submergence avoidance was carried out with marker genotype data. As a result, three (on chromosomes 2, 3 and 10) and two QTLs (on chromosomes 3 and 4) were found in the BRILs having genetic backgrounds of Nipponbare and IR36, respectively. Of these, one each had the wild allele with increasing effect on shoot length. These favorable wild alleles would be useful in improving direct-seeding cultivation in water-prone areas.

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This study was conducted to clarify the cause of growth inhibition of rice cultivar for whole crop silage 'Hyogoushiwakamaru' in Awaji region (the southern part of Hyogo prefecture) in 2007. The genetic natures of 'Hyogoushiwakamaru' and the breeding lines were investigated. As a result, being ruled by single inferiority gene became clear as for the sensitivity to paddy herbicide, Benzobicyclon. This sensitivity was derived from indica-type high-yielding rice cultizar 'Tokusei' breeded by Guangdong province in China.

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This study conducted covariance structure analysis in order to quantify the relationship among factors which caused field-to-field variability in 'Tanbaguro' production, using the data obtained by field investigations for 3 villages of Kyoto prefecture in 2007 and 2008. Firstly, we developed a structure equation model including 26 observed variables and 8 latent variables. The observed variables were consisted of soil chemical properties, weather condition and crop growth. The model explained 68% of sample covariance matrix which consists of covariance among observed variables. However, result suggested that the model was unstable because of too many factors. Accordingly, we improved the model by reducing the factors on the basis of causal coefficients. The improved model obtained 14 observed variables and 3 latent variables, and explained 79% of the sample covariance matrix. The improved model also suggests that early growth is important to obtain higher yield, and that yield and grain size are closely related with nitrogen status in a plant which defined by nodule condition and leaf color. The effect of water should be incorporated to the model in the next step.

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In order to elucidate transposition mechanism of rice active transposon mPing, we must accurately detect transposition of mPing. Although transposon display is a powerful tool for exhaustively evaluating insertion sites of mPing, we often encounter difficulties to eliminate false-positive results. In this study, we tried to establish high-fidelity transposon display for mPing. We modified reaction conditions of genomic DNA digestion and adapter ligation, and used restriction enzyme-digested first PCR products as a template DNA in second PCR. Consequently, we successfully eliminated false positive results.

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The flowering traits of 'Emmer' and 'Pyramidale', two ancestral wheat varieties that are now used to make two types of beer brewed in partnership with Kyoto University scientists, were investigated in detail. These varieties are classified as T. turgidum L. ssp. dicoccon and ssp. turanicum, respectively, and little information is available about their agronomic characteristics. Through evaluation of the internal factors determining their flowering time (photoperiodic response, vernalization requirement and narrow-sense earliness), we revealed that the two varieties are spring-habit and photoperiod-sensitive. While the narrow-sense earliness of 'Emmer' is less intense than that of 'Pyramidale', the photoperiodic response of 'Emmer' is more intense than that of 'Pyramidale'. Based on a genetic analysis using the F₂ population of the two varieties, we concluded that 'Pyramidale' harbors a photoperiod-insensitive allele in the Ppd-A1 locus, the same allele reported by Wilhelm et al. (2009). This photoperiod-insensitive allele is expected to be a useful genetic resource in the breeding of tetraploid and hexaploid wheat.

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A rice cultivar 'Akino-uta' bred in Shiga Prefecture Agricultural Technology Promotion Center, is sensitive to panicle blast. To develop an Akino-uta near-isogenic line harboring the panicle blast Pb1, we investigated the applicability of three molecular markers, B1, B2 and B4, which are linked to Pb1, to 'Akino-uta'. As a result, the genotype of 'Akino-uta' using these molecular markers was the Modan-type (Pb1 harboring-type), which did not correspond with the panicle blast-susceptive phenotype of 'Akino-uta'. In this study, we sequenced a neighboring region of Pb1 from 'Akino-uta' and 'Koshihikari Aichi SBL' harboring Pb1 gene. Comparison of the sequences revealed that the reactivity of these molecular markers to 'Akino-uta' was caused by the sequence homology in both cultivars. Moreover, we analyzed genotype of 'Akino-uta' with PCR-marker, N3-2, which is linked by 0.0cM to Pb1 gene. Consequently, 'Akino-uta' did not harbor Pb1 gene. This case is the first report of molecular markers for selection of the Pb1 gene in japonica rice cultivar. When the genotype is of the Modan-type using molecular markers, B1, B2 and B4, in japonica rice cultivar, we should consider using other markers, N3-2 and so on, with them.

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Seed germination of sesame (Sesamum indicum L.) and its wild relative S. mulayanum Nair was examined, focusing on dormancy break of S. mulayanum. S. indicum showed higher germination (%) at 30 and 35℃ as compared to that at 25℃, while S. mulayanum showed deep dormancy and failed to germinate at all temperatures tested. Soaking seeds in gibberellic acid (GA3) solution had no effect on seed germination of S. mulayanum at any concentration (5, 10, 50, 100 and 200μM) of GA3 tested. Treatment of the scarification promoted seed germination of both S. indicum and S. mulayanum and completely broke seed dormancy of S. mulayanum resulting in 90% germination. The present method for seed dormancy break is expected to aid the examination of inheritance mode of seed dormancy in the crossed progeny between the two species.

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In order to minimize the environmental pollution of the Lake Biwa, rice has been cultivated under low imput of chemical fertilizer and agricultural chemicals since 2001 in Shiga-prefecture. Under these situations, the amount of nitrogen application is less than that in the traditional cultivation. Present status of the yield, dry matter production, or nitrogen balance between application and absorption in such a cultivation are not yet known so much. Therefore, the investigation were carried out to resolve those questions. Yield and dry matter production of the investigated low imput rice were not so high. But the yield of whole rice which includes traditional cultivation in Shiga-prefecture was 525.3kg/10a, and the yield were almost not changed since 2001. These indicate that the yield of low imput cultivation is approximately as same as that in traditional one. Dry matter production of the low imput rice was not so high. because of the shortage of the number of panicles. The amount of absorbed nitrogen by the low imput rice exceeded to that of application. Therefore, it may be considered that the severe decrease of soil fertility would occur according to long continuation of such cultural practice. The straw, whose dry weight is almost same as that of panicles weight and which contains considerable amount of nitrogen together with carbon, should be returned to the paddy field to maintain the soil fertility.

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The study area was abandoned about 20 years ago in Nose. Three varieties of rice 'Kinuhikari', 'Asamurasaki' and 'Akamochi' were cultivated in this abandoned terraced paddy fields without chemical fertilizer. For comparison the same variety of rice were cultivated in ordinal paddy field of Sakai with chemical fertilizer. Panicle length, culm length and 1000-grain weight of all variety in Nose were lower than Sakai. Panicle number and ripened filling of 'Kinuhikari' and 'Akamochi' in Nose, however, were higher than Sakai. The yield of 'Kinuhikari' in Nose was slightly lower, but was not significantly different each other, and Akamochi's yield in Nose increased more than 10% of Sakai. Solar radiation and temperature in Nose were lower than Sakai. These atmospheric conditions caused delay heading and higher ripened filling. These results suggest that abandoned paddy fields are capable to cultivate rice without chemical fertilizer.

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