Grain yield of rice plants is composed of different yield components that vary with the genotype, environmental condition and cultivation practice. Experiments were conducted in 1999, 2000 and 2001 in the field of Iwate University, Japan to study the responses of yield components to the practice of nitrogen-free basal dressing accompanied with sparse planting density (BNo) in 12 rice cultivars or lines. The results showed that the number of spikelets per panicle (NSp^-1), especially in the late-maturing cultivars and in 2001, was often larger in BNo than in the conventional cultivation (CONT). The number of panicle m^-2 (NPm^-2), however, was significantly smaller in BNo than in CONT, resulting in a small number of spikelets m^-2 (NSm^-2) in BNo. The difference between BNo and CONT in NSm^-2 varied with the cultivar and the year, and it was often smaller in the late-maturing cultivars than in the early- and medium-maturing ones, and was also smaller in 2001 than in 1999 or 2000. The percentage of ripened grains (PRG) was higher in BNo than in CONT in all cultivars, and the average PRG of 12 cultivars in BNo was 14.0%, 9.0% and 4.8% higher than that in CONT in 1999, 2000 and 2001, respectively. Grain weight (1,000-grain weight) was heavier in BNo than in CONT in most cultivars, and the 1,000-grain weight averaged over cultivars and years was 0.8 g (3%) heavier in the former than in the latter. High temperatures during the grain-filling period significantly and adversely affected 1,000-grain weight in CONT, but only slightly in BNo. The stably high PRG and heavy 1,000-grain weight in BNo, especially in the year with unfavorable weather (1999), could compensate for the small NPm^-2 in BNo so as to achieve a high and stable yield in the Tohoku region.

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Dynamic states of water in the leaves and roots of perennial ryegrass (Lolium perenne L.) exposed to cold and heat stresses were studied by using ¹H-NMR. NMR spin-lattice relaxation times (T₁) of leaves in Arrhenius plots linearly decreased but increased as temperature decreased below 0°C. However, spin-spin relaxation times (T₂) of the leaves increased as temperature decreased from 20 to -20°C. TheT₂ value of the long fraction (associated with vacuole) in leaves decreased to about 600μs at -25°C, but that of the short fraction was about 10μs, and the relative value of signal intensity of the long fraction decreased to about 0.2 at -25°C. The T₂ values of the two fractions in roots decreased to about 1ms at -10°C. Judging from T₂ and electrolyte leakage, both vacuolar and cytoplasmic compartments of leaves and roots froze at these temperatures. T₁ of the leaves decreased slightly as temperature increased from 20 to 40°C but greatly decreased as temperature increased further. On the other hand, T₁ of the roots decreased linearly as temperature increased from 20 to 50°C. The levels of electrolyte leakage from leaves exposed to the above heat stress was low suggesting that membrane was not severely injured. In conclusion, analysis of Arrhenius plots of T₁ and T₂ is a sensitive and non-invasive method to evaluate primary responses of perennial ryegrass organs to the temperature stresses.

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Drought is one of the major constraints for soybean production in Brazil. Seed yield of ten Brazilian soybean cultivars sheltered from rain (drought stress) for one month after the first flowering was examined over two growing seasons in the field in Londrina, Brazil. The drought tolerance on the basis of seed yield varied with the cultivar, and the yield ranking among cultivars was nearly the same across two years. In cultivars with higher drought tolerance, crop growth rate (CGR) during the drought stress period was higher than in other cultivars. They also maintained a larger leaf area during the stress period. Although reproductive development was retarded by the drought stress, it tended to be retarded less in drought-tolerant cultivars. The information obtained in this research may be useful for breeding drought-tolerant cultivars or selecting diverse germplasms of soybean cultivars.

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The critical developmental stage, during which the genotypic difference in yield is determined, was identified by analyzing the correlations between seed yield and seasonal crop dry matter productivity in optimally managed fields in four seasons. The fields (fluvial sandy loam or clay loam) were managed with irrigation, pest and weed control and canopy support to prevent lodging whenever necessary. The tested genotypes included 11 Japanese old and modern cultivars, five US cultivars and one non-nodulating line. Four to eight cultivars were studied in each year. Seed yield with 15% moisture (Y) in each experimental plot varied from 255 to 498g m^-2. The US cultivars and Japanese modern cultivars tended to have a higher yield than the other cultivars grown in the same year. Y significantly and positively correlated with crop growth rate (CGR) during the 20 d period after the beginning of seed filling (R5), i.e. initial seed filling stage, in all four experiments. On the other hand, correlation of seed yield with CGR before or after this period varied with the year from negative to positive correlations. A close correlation was also observed between pod growth rate during the initial seed filling and Y. These results suggest that the critical stage during which seed yield potential of soybean cultivars is determined is the initial seed filling period and the larger dry matter production during this period is closely associated with the satisfactory growth of reproductive organs and high seed yield.

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We found in the previous study that the wheat plants grown under relatively low soil moisture conditions (D plot) could attain heavier dry matter than the plants watered on the basis of average local precipitation (W plot). The aim of this study was to make a detail analysis of the ecophysiological characteristics that cause the difference in dry matter production between the plants in the W and D plots under different soil moisture conditions. Soil matric potential at a depth of 30 cm was kept at about -4 kPa in the W plot. It decreased gradually after watering at about one month before heading and at heading, reaching about -80 kPa at heading stage and at the mid-ripening stage respectively, in the D plot. The plants in the D plot produced heavier dry matter and a better developed root system than the plants in the W plot. The higher net assimilation rate and larger leaf area, which accounted for the higher crop growth rate of the D plot, were due both to avoiding suppression of the photosynthetic rate and leaf expansion owing to water stress, and to maintaining high rates of leaf photosynthesis and a large leaf area during leaf senescence. A larger amount of nitrogen was accumulated at the flowering stage and the nitrogen content of leaves remained higher during senescence in plants in the D plot than those in the W plot. The activity of cytokinins in the xylem sap was higher in plants in the D plot. These characteristics might have contributed to the delay in the decline in the rate of photosynthesis and in leaf area during leaf senescence and seemed to be supported by the enhanced development of the root system under moisture-restricted conditions.

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Experiments were carried out in 1999, 2000 and 2001 on the field of Iwate University, Japan to examine the effect of nitrogen-free basal dressing accompanied with sparse planting density (BNo) on the dry matter production (DMP) of 12 rice cultivars or lines belonging to the early, medium and late-maturing genotypes. During the period from transplanting to panicle initiation (PI), DMP was lower in BNo than in the conventional cultivation (CONT) in all 3 years. The DMP during the period from PI to full heading (FH) was also lower in BNo than in CONT, particularly in the high solar radiation year of 1999, because of the small leaf area index. During the ripening stage, leaf area index in BNo was smaller, but crop growth rate in BNo was similar to or higher than that in CONT due to the large net assimilation rate, which resulted from the large flag leaf and 2nd leaf, and the heavy specific leaf weight in BNo. The DMP per panicle during the period from PI to FH positively and significantly correlated with the number of spikelets panicle^-1. The percentage of ripened grains (PRG) was also closely related with the amount of carbohydrates from stems (−ΔS) and photosynthesis after FH (ΔW) contributed to a spikelet during the early ripening period (during 20 days after FH). The higher DMP per panicle in BNo compared with CONT during the period from PI to FH, therefore, resulted in a larger number of spikelets panicle^-1 in the former. On the other hand, the large amount of carbohydrate supply per spikelet during the early ripening period could also secure a high and stable PRG in BNo, especially under unfavorable weather conditions.

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The supernodulating soybean cultivar Sakukei 4 was previously characterized by its superior ability to maintain a high leaf nitrogen (N) content and high photosynthetic rate. Despite these desirable traits, the growth performance of Sakukei 4 was inferior to that of its normally nodulating parental cultivar, Enrei. The physiological basis for the unique growth characteristics of Sakukei 4 remains unclear. The objective of the present study was to characterize in further detail the vegetative growth of Sakukei 4, particularly during the period before pod expansion. In the first experiment, the growth of Sakukei 4 was compared with that of its parental cultivar Enrei under various rates of N fertilizer. The dry weight of tops, roots and nodules of the plants grown at lower rates of N application was greater in Enrei than in Sakukei 4, but it was vice versa at higher rates of N application. The number and weight of nodules were far greater in Sakukei 4 than in Enrei at any rate of N application. These genotypic differences were significant on 39 days after sowing (DAS) and became greater at the flowering stage. In the second experiment, therefore, more detailed growth analysis was made during an earlier growth stage (DAS 31-46). During this period, relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) were lower in Sakukei 4 than in Enrei and the related non-nodulating line En1282, whereas the leaf photosynthetic rate was higher in Sakukei 4 at all leaf positions. The dry-matter partitioning to each plant part excluding nodules was similar in all three genotypes. The rate of leaf expansion in Sakukei 4 during this period was significantly slower than that in the other genotypes. These results suggest that the inferior growth of Sakukei 4 prior to flowering is probably due to excessive dry-matter partitioning to nodules and depressed capability of leaf expansion and root growth, which might limit dry-matter production of the whole plant during pre-flowering stage.

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Characteristics of flowering and pod set were compared between wild and cultivated types of soybean grown in pots (1/5000 a) in a vinyl house. The wild type had 10-fold more nodes than the cultivated type. The flowering habit of the wild type was similar to that of the indeterminate type. The wild type developed 10-fold more flowers than the cultivated type, but set relatively few pods. During the process of domestication from wild to cultivated type, i) the pole climbing characteristic disappeared and development of branches and racemes with compound leaves was repressed, resulting in a decreased number of nodes, ii) flower production decreased and the rate of pod set increased markedly, and iii) the number of pods decreased, but seed size became bigger.

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Aroma strength of aromatic rice varies with the genetic and environmental conditions. We determined the concentration of 2-acetyl-1-pyrroline (2AP), a key compound of the aroma of aromatic rice, in 62 samples of rice grains (brown rice) from 'Hieri' produced by 17—24 farmers in 3 years in the Kubokawa area of Kochi Prefecture, Japan. Many of them showed similar values and the standard deviations were 27—31%. However, a few samples showed extremely high (200%) or low (60%) 2AP concentrations compared to the individual year averages (100%). The influence of harvest time and temperature during ripening on the 2AP concentration in the brown rice was also examined using two cultivars. During grain development in an early-heading cultivar 'Miyakaori' , the 2AP concentration in the brown rice reached a peak at 4 or 5 weeks after heading (WAH) and then decreased rapidly to 20% of the maximum at 7 or 8 WAH. In a late-heading cultivar 'Hieri', the 2AP concentration peaked at 4 WAH then gradually decreased to 40% of the maximum at 8 WAH. The 2AP concentration was higher in brown rice ripened at a low temperature (day : 25°C/night : 20°C) than that ripened at a high temperature (day: 35°C/night: 30°C) in both a short-grain cultivar 'Hieri' and a long-grain cultivar 'Sari Queen'.

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The relation between the source capacity of leaves and the sink capacity of panicles affects dry-matter production and determines grain yield in rice. The source-sink relation has so far been studied on rice plants from which panicles were artificially removed. We examined the source-sink relation using a female-sterile line FS1 with intact panicles each having a few fertile grains instead of panicle removal. The leaf photosynthetic rate during the ripening stage in FS1 was measured, in comparison with a normal counterpart Fujisaka 5, and the effect of losing sink function on dry-matter production in the rice plant was characterized. The photosynthetic rate in flag leaves was maintained at a slightly higher rate in FS1 than in Fujisaka 5 in the late ripening stage, though panicles did not function as a sink organ in FS1, and dry-matter production in this line was not lower than that in Fujisaka 5. In the early ripening stage of FS1, culms and leaf sheaths fulfilled the sink function instead of panicles, and the tillers that appeared in the late ripening stage became a new sink organ. Roots also functioned as a possible sink of photosynthates. Owing to the unique character of dry-matter production after heading, FS1 may be useful as a forage crop.

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We aimed to determine the orientation for developing the method to estimate leaf area of sago palm (Metroxylon sagu Rottb.) by extracting characteristics that might be related to estimating leaf area from characteristics of leaves. Plants of around two years after trunk formation at a sago palm farm in Sarawak, Malaysia were used for the investigation. In a plant with eleven living leaves, the length of the unfolded leaf blade ranged from 6.0 to 7.2 m; the length of a petiole ranged from 1.8 to 3.1 m. The number of leaflets on the left side of a leaf viewing adaxial leaf surface with the tip upward was larger than that on the right side by 1-5 leaflets in all leaves. The lowest leaflet of a leaf was on the left side in all leaves. The relative position of the lowest leaflet on the rachis was related to the way a leaf was folded in a plant. The length, width and area of the right and the left leaflets were compared on the basis of their position on a rachis. They had approximately the same dimensions. This fact implied that those characteristics were almost symmetric with respect to the rachis; therefore, the position of a leaflet on a rachis was considered to be an important characteristic for analyzing leaf area. We drew a leaf diagram based on the measured data and examined a method of estimating leaf area using the leaf outline, but the method was not suitable. We decided to examine a method to integrate the leaflet areas for accurate estimation of the leaf area.

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This study was carried out to verify the production of haploid plantlets through somatic embryogenesis of Bupleurum falcatum in anther culture (2n=16). Flowers with anthers at the uninucleate stage, less than 200μm in anther length, were exposed to 10°C for 5 days (cold pretreatment) and the anthers were cultured on MS medium supplemented with 2,4-D and/or picloram at various concentrations at 30°C. The optimal supplement for callus formation was a mixture of 0.075 mg ^-1 2,4-D + 0.075 mg L^-1 picloram or 0.75 mg ^-1 2,4-D without picloram. Only a few calli were induced from the anthers without cold pretreatment. The calli were transplanted to MS medium without phytohormones and cultured at 25°C for plant regeneration. Among one hundred twenty root tips of the regenerated plantlets examined, 14.2% were haploid (n=8). However, in the plantlets regenerated from anthers without cold pre-treatment only 2.5% was haploid. In both haploid and diploid regenerated plantlets, the chromosome number was fixed without variation. Among the regenerated plantlets, one was albino. Haploid plantlets were transplanted to the field after acclimation in pots filled with vermiculite under 90% humidity for a month, and haploid plant were produced. The potential of haploid plants derived from anther culture for production of high-yield and good-quality cultivars is discussed.

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Sixty tartary buckwheat (Fagopyrum tataricum) strains were investigated for grain shedding habit, plant height, grain yield, dry weight of plant, weight of grain, days to flowering after sowing and DNA content of nuclei. The grain shedding habit was evaluated from the breaking strength of pedicel and the percentage of the grains dropped by threshing. DNA content of nuclei was detected by flow cytometry to classify the polyploidy level. The fluorescence intensity of the flow cytometry demonstrated no difference between common buckwheat (F. esculentum) and tartary buckwheat, but a clear difference was detected between the diploid and the autotetraploid strains. The survey of DNA content of the 60 tartary buckwheat strains revealed that most of the strains were diploids, but one strain was autotetraploid. The autotetraploid strain exhibited less grain shedding, and produced the largest grains among the strains tested. However, the other characters of the autotetraploid strain, such as plant height, grain yield, dry weight of a plant, and days to flowering, were similar to the mode of the traits of the diploid strains.

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The objectives of this study were to determine the genetic diversity of Japanese cultivated sorghum (sorghum lines cultivated in Japan), using the simple sequence repeats (SSR) technology and to determine the diversity of sorghum breeding germplasm accessions and their relationship with Japanese cultivated sorghum. The cluster analysis of SSR data showed that Japanese cultivated sorghum showed a wide genetic background, but the lines from the same breeding station tended to have a close genetic background. Sorghum breeding germplasm accessions that included lines from ICRISAT, U.S.A., Japan, and improved lines (elite inbred lines) showed a narrower genetic background than Japanese cultivated sorghum and were distinctly separated from them. An efficient method of using germplasm as a genetic resource is proposed.

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Potted mulberry plants (Morus alba L. 'Shinn-ichinose') were grown in phytotrons under natural sunlight, and their shoot growth response to temperature and photoperiod was investigated. A short photoperiod caused cessation of shoot growth, and this effect was prominent at 20°C. Temperatures higher than 24°C activated the growth activity for mulberry shoot growth. Temperature had two effects on mulberry shoot elongation. One was to control the growth activity of mulberry shoots, and the other was to determine the potential rate of shoot elongation, which is realized at the maximum growth activity under a given environmental condition. On the basis of these results, the effect of temperature and photoperiod on the cessation of mulberry shoot elongation was simulated in a non-linear regression model. The values of shoot length predicted by the model differed somewhat from the measured values in some plots, most likely because the timing of shoot growth cessation differed with the year. However, on the whole, shoot length predicted by the model seems to fit the measured values well.

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We examined the possible benefit of rational site-specific crop management practices in 17 paddy fields located in an area of 2.0 ha for the prevalence of precision agriculture methods on a cooperatively managed large-scale farm in Sakurai, Nara Japan. Data on grain yield, soil physicochemical properties and farmer's crop management practices were collected in each paddy field. Unhulled rice yield was estimated at a resolution of 5m×5m in an area of 1.2 ha using a yield-monitoring combine. The spatial distribution of the variations for the collected data was characterized using geostatistical procedures. The kriged map of the unhulled rice yield drawn from the results of geostatistical analysis indicated the potential value of rational site-specific crop management using the yield-monitoring combine. The ratio of spatially structured variation to the total variation of brown rice yield, that is, the controllable proportion to total variation, was 75.4%. Each yield component i.e., the number of spikelets per square meter, filled-spikelet percentage and 1000-grain weight contributed 33.7%, 54.7% and 11.6%, respectively, to brown rice yield. These three yield components combined contributed to 96.5% of the brown rice yield variation. The agronomic factors (soil fertility factor, early growth factor, N dressing and uptake factor) contributed 79.7%, 52.1% and 41.8%, respectively, to the variation of these three yield components. Therefore these agronomic factors accounted for 58.1% of the total variation of the brown rice yield and 77.1% (i.e. 58.1% out of 75.4%) of the spatially structured variation of the brown rice yield. This controllable proportion may be a criterion for the prevalence of site-specific crop management in large-scale farm management in general, although only one case study was conducted.

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