At present, the main challenge in rice production is to achieve a high and stable yield with low input. In this study, the growth of tillers and yield of 12 rice cultivars and lines in the practice of nitrogen-free basal dressing with sparse planting density (BNo) was examined and compared with those in the conventional cultivation (CONT). The results in 1999, 2000 and 2001 showed that the numbers of both primary and secondary tillers m^-2 were smaller in BNo than in CONT for all cultivars. However, a large number of tillers in CONT, especially the secondary tillers, were nonproductive, and most of those in BNo were productive. The difference between BNo and CONT in the number of panicles m^-2 was larger for the cultivars of the panicle-number type than for those of the panicle-weight type. Grain yield was often lower in BNo than in CONT, and the yield averaged over years and cultivars was 748 g m^-2 in BNo and 772 g m^-2 in CONT (the ratio of value in BNo to that in CONT was 97 %). The difference between BNo and CONT in grain yield varied with the cultivar and the year. Under favorable weather conditions in 2000 and 2001, grain yield was high in both CONT and BNo, and was higher in CONT than in BNo for most cultivars. Nevertheless, under the unfavorable weather condition in 1999, grain yield was low in both CONT and BNo, and was similar or higher in BNo than in CONT. In all 3 years, the grain yield of Akitakomachi and Fukuhibiki was lower, and that of Ouu316 and Hitomebore tended to be higher in BNo than in CONT. The practice of BNo was found to be effective for achieving a stable and high yield of Ouu316 and Hitomebore in the Tohoku region.

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The objective of this study is to elucidate the effects of CO₂ enrichment during different growth periods on flowering, pod set and seed yield in soybean (Glycine max (L.) Merr.). Soybean cultivar ‘Fukuyutaka’ was grown in a growth chamber of the Institute of Bioresources Research Center of Kyushu Electric Power Co., Inc. at Saga, Japan (33°17′-N, 130°18′-E) under natural light. The CO₂ concentrations were maintained at 350 μmol mol^-1 for ambient CO₂ and at 700 μmol mol^-1 for CO₂ enrichment. CO₂ concentration was elevated during the whole growth period (WP), vegetative growth period (VP) or reproductive period (RP). Seed yield was increased by CO₂ enrichment during RP or WP due to the increase of pod number, but not by CO₂ enrichment during VP. Although CO₂ enrichment had no effect on the number of flowers, CO₂ enrichment during RP increased the pod number on all raceme orders and that during WP increased the pod number in the secondary and tertiary racemes. It is suggested that an increase of seed yield by CO₂ enrichment is mostly brought by the improvement of pod set, mainly on the high-order racemes that opened later during flowering period, and that the response of seed yield to CO₂ enrichment is mainly attributed to the response during RP.

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Proteins and carbohydrates in developing rice panicles were analyzed to see whether these parameters control spikelet number in rice. Two rice cultivars and 2 levels of nitrogen topdressing were used to obtain panicles with different numbers of spikelets. A japonica rice cultivar, Nipponbare, with topdressing (H) had 1.8 times more spikelets per panicle than that without topdressing (L). Moreover, the number of spikelets per panicle in an indica rice cultivar, Takanari, without topdressing was 2.7 times larger than that in Nipponbare-L. Panicles with more spikelets (LP) in Nipponbare-H and Takanari-L showed slower growth than those with few spikelets (SP) in Nippanbare-L in an early stage. LP, however, increased markedly in size thereafter, eventually exceeding SP, in length and fresh weight. Soluble protein content was higher in LP than SP in an early stage, but this difference was hardly detected in a late stage. No clear difference was observed in sugars or starch between LP and SP. Analysis of soluble and insoluble proteins by SDS-polyacrylamide gel electrophoresis showed that bands corresponding to insoluble proteins with a molecular weight about 42 kDa were present at higher intensities in LP than in SP. These results suggest that the spikelet number in rice is controlled by the soluble protein content in an early stage and insoluble proteins with a molecular weight of 42 kDa during panicle development, but not by the carbohydrates in developing panicles.

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The thermo-sensitive genic male sterile (TGMS) T29^s line was sterile when exposed to daily mean temperatures of 24.1°C or above during the critical stage (from 15 to 11 days before heading). It was completely sterile for both pollen and spikelet when the plant headed from June 16 to November 7 in Okinawa, because the temperature exceeded 24.1°C. The heterosis of the F₁ hybrids between the T29^s line and seven indica cultivars was examined. Most of the F₁ hybrids showed positive heterosis over the male parent for grain yield per plant and the number of spikelets per panicle, and one of them manifested heterosis for grain yield over a F₁ hybrid from a cytoplasmic male sterile (CMS) line. Dry matter accumulation per plant at the panicle initiation stage in most F₁ hybrids was higher than that in the respective male parent or mid-parent, and it was correlated with a larger number of tillers and leaf area per plant. All F₁ hybrids produced a larger number of panicles per plant than their respective male parent. Positive heterosis over the male parent for the number of filled grains per panicle, 1000-grain weight and harvest index was obtained in several F₁ hybrids. A positive correlation was found between grain yield and the dry matter accumulation per plant in F₁ hybrids. Both the larger number of panicles per plant and the larger number of spikelets per panicle were more important for the positive heterosis for grain yield in F₁ hybrids rather than the higher 1000-grain weight. Among the yield attributes, a larger number of filled grains per panicle mainly contributed to a higher grain yield of F₁ hybrids.

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The tolerance of six cool-season grasses and six warm-season grasses to three kinds of salt was examined in solution culture. Among the cool-season grasses, tall fescue (Festuca arundinacea Schreb.) was the most tolerant to all three salts. Among the warm-season grasses, bermudagrass (Cynodon dactylon (L.) Pers.) was the most tolerant to excess calcium chloride and sodium chloride, while bahiagrass (Paspalum notatum Flugge) was the most tolerant to excess magnesium chloride. A positive and significant correlation was found between estimates of the concentration at which plant growth decreases by 50% (C₅₀) in the presence of excess CaCl₂ and those in the presence of excess NaCl. The C₅₀ estimates in excess MgCl₂, however, were not correlated with those in the other two salts. The results suggest that common physiological mechanism confers tolerance to both excess CaCl₂ and excess NaCl, but a different mechanism to excess MgCl₂.

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A retrospective analysis of the physiological basis of genetic yield improvement should provide us a direction for future yield improvement. The objectives of the present study were to evaluate the change in yield in leading rice cultivars that were bred and grown in the Tohoku region in the 20th century, and to find whether apparent photosynthetic rate (AP) is associated with the yield improvement. Ten leading rice cultivars were grown at low- and high-nitrogen conditions, Low-N and High-N, respectively, and three environmental conditions (two years in Sendai and one year in Kashimadai). Yields were higher under High-N than under Low-N in all the cultivars tested, and yield increase was greater in the newly bred cultivars released after 1960s (new cultivars) than in those released before 1960 (old cultivars). The genotypic improvement in yield under High-N was progressive year by year in the old cultivars whereas it was stagnated in the new cultivars. The cultivar difference in AP of the flag leaf one week after heading was small, but that three weeks after heading was larger in new cultivars than in old cultivars except for a few cultivars. A dependence of AP on leaf nitrogen concentration three weeks after heading was evident in the plants grown under High-N. The number of spikelets increased under High-N in all ten cultivars, where the percentage of ripened grains was lower in the old cultivars than in the new cultivars. These results suggest that yield improvement of rice cultivars in the 20th century in the Tohoku region has been accompanied by a greater AP during the ripening stage that might lead to a greater grain filling percentage.

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We improved the aluminum borate whisker-mediated method of DNA delivery into rice callus (Oryza sativa L., cv. Notohikari). The following factors were examined: amount of whiskers, the kind of apparatus for agitation, the type of whiskers, duration of agitation, and agitation speed. Twenty callused scutellar tissues were agitated in a 1.5 ml microtube containing aluminum borate whiskers (ABW), liquid medium, and the plasmid pAct1-F carrying the ß-glucuronidase (GUS) gene. After the agitation, the scutellar tissues were subjected to transient GUS expression assay, which visualizes GUS-expressing cells as blue spots. Efficiencies of DNA delivery were evaluated as the number of blue spots resulting from the assay. In the present study, we succeeded in improving the efficiency of DNA delivery by changing the apparatus for agitation from rotary (Vortex Genie 2) to multidirectional (MT-360), and the type of ABW from Alborex Y to an aminosilane-coated Alborex (Alborex YS3A).

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Azolla (Azolla anabaena) is an aquatic fern plant that can be used as a green manure and organic matter resource in many countries where irrigation water is not a problem. A. mexicana is one of the azolla species adapted to the environmental conditions of Izmir (Turkey). The objective of this research was to determine the adaptation and agronomic potential of azolla plants to the Mediterranean climate regions. The research was conducted at three locations (Izmir and Aydn located in the Aegean region and Antalya located in the Mediterranean region of Turkey) in 1999, 2000 and 2001. Fresh azolla was planted in April, May, June and October at the rate of 300 g m^-2 at each application. The growing azolla plants were harvested 15 days after planting. The highest fresh yield (1481 g m^-2) was obtained in April at Izmir. The total N, P, and K values were between 2.93-3.31 %, 0.43-0.54 % and 1.10-1.37 % at Izmir, Aydn, and Antalya, respectively. The shortest time to reach a two-fold increase was 3.53 days at Izmir based on the average of three years.

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We screened regenerable genotypes from 12 cultivars of Italian ryegrass (Lolium multiflorum Lam.) through tissue culture of mature seeds, shoot tips and root tips. Although three morphological types of calli, friable, watery, and compact with fine root hair were observed, green shoots regenerated only from the friable calli. The highest frequency of the formation of regenerable callus from mature seeds was 1.4% in the diploid cultivar Waseaoba and 1.1% in the tetraploid cultivar Meritra. The plants regenerated from mature seed-derived calli were maintained and propagated aseptically in vitro, and the method of regenerating plantlets via callus culture was established by using their shoot tips. Sixty-three seeds of Waseaoba and 44 seeds of Meritra were aseptically sown, each seedling (genotype) was propagated in vitro, and the shoot tip from each genotype was subjected to tissue culture. More than 22% of these genotypes formed regenerable calli. From these results, we conclude that the shoot tip of the in vitro-preserved plantlet is useful for producing the regenerable calli routinely. The information obtained in the present study is useful for establishing a reliable transformation system for Italian ryegrass.

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Phasic development of rice is influenced by various climatic conditions and the nursery duration. As a step toward the analysis of yield potential and yield loss in the Red River Delta, Vietnam, we conducted field trials with different nursery durations and transplanting times to develop a model for estimating heading times of a non-photosensitive cultivar CR203 in the Red River Delta. Days from seedling emergence to heading varied from 73 to 106 d, the rainy season crops having a shorter duration than the winter-spring season crops. The heading time could generally be estimated by the function of air temperature, but the delay in heading due to transplanting (transplanting shock), defined as the difference in the days from emergence to heading between transplanted and direct-seeded rice, ranged from 1 to 9 d and caused a substantial error in the heading time estimation. This variation in the delay of heading was explained as a function of the seedling age at the transplanting time. The model considering the transplanting shock estimated the heading dates in the independent data sets obtained at fields of local farmers with root mean square deviation (RMSD) of 2.15, while the model not considering the transplanting shock estimated those with a RMSD of 3.34. We conclude that this simple transplanting shock model was applicable for estimating the rice phasic development in the Red River Delta.

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A substrate-induced respiration (SIR) method combined with selective inhibition for estimating the fungal and bacterial biomass of volcanic ash of Kanto Loam type (Humic Andosols) was developed. The optimum time for CO₂ measurement was 2-4 hr after glucose application and the amount to be applied was 2000 ppm on a soil dry weight basis. CO₂ evolution from the soil correlated with the amount of microbial biomass carbon estimated by the chloroform fumigation extraction (CFE) method and a linear relationship, biomass C (μg g^-1 dry soil) = 81.9 x CO₂ (μl g^-1 dry soil hr^-1), was obtained between them. Cycloheximide (1000-8000 ppm) and chloramphenicol (500-2000 ppm) effectively inhibited SIR but streptomycin (500-2000 ppm) did not. The combination of 2000 ppm cycloheximide and 1000 ppm chloramphenicol showed the best additivity and enabled the measurement of the proportions of fungal and bacterial biomass. The SIR method combined with the selective inhibition technique was applied to soil samples from a maize field. The total microbial biomass was higher in the soil where green manure had been incorporated. The fungal-to-bacterial ratio increased from 1.1 at the time of maize sowing to 1.4 at the time of maize harvest.

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To evaluate the feasibility of conservation tillage in combination with reduced biocide and fertilization regimes, we conducted a field experiment using conventional and reduced tillage, with or without reduced biocide, and fertilization regimes for growing soybean, sugar beet, and spring wheat in this order for three years. Root biomass and sugar yield of sugar beet did not differ with any combinations of conservation practice. Although leaf biomass was significantly reduced under reduced chemical fertilization (replaced partially with manure compost), it was compensated by a greater specific leaf area. Early crop growth of soybean, and spring wheat was increased to some extent under reduced tillage, which indicated a better nutrient utilization, as well when combined with reduced biocide application. However, reduced fertilization could not supply as much nitrogen as conventional chemical fertilization especially in the combination with reduced tillage. Larger amount or long-term application of organic fertilization may be necessary under reduced tillage compared to the requirement under conventional tillage to compensate for lower rate of nitrogen release from organic matter.

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The effects of cutting interval and cutting height on dry matter productivity and overwintering ability were compared among 4 Pennisetum species, napiergrass, kinggrass, hybrid napiergrass and pearl millet in the established year to examine the suitable cutting practice for the productivity and persistence. The cutting intervals were 60 and 90 days, and the cutting heights were 0 and 30 cm above the ground. Annual herbage dry matter yield (HDMY) was the highest in kinggrass, followed by hybrid napiergrass, napiergrass and pearl millet, and was higher in the plants at a 90-day interval and 0-cm height than at a 60-day interval and 30-cm height, respectively. The percentage of dry matter to fresh matter did not correlate with the annual HDMY or cutting height. The plants cut at a 90-day interval at a 0-cm height had the highest in mean tiller weight, crop growth rate, net assimilation rate and HDMY, but the lowest tiller number and percentage leaf blade to the whole harvested plant. Thus, the correlation coefficients between HDMY and plant characters were positive for plant height, mean tiller weight, leaf area index and crop growth rate in all 4 species and were negative for tiller number and percentage leaf blade except for pearl millet. Both percentage overwintered plants and regrown tiller number were the highest in kinggrass followed by napiergrass and hybrid napiergrass; these were nil in pearl millet under all cutting practices, and were higher in the plants cut at a 30-cm height than at a 0-cm height. This tended to be associated with higher tiller bud number and higher total nonstructural carbohydrate concentration in the stubble after cutting at a 30-cm height. Regrown tiller number was higher in the plants cut at a 60-day interval than at a 90-day interval in all species except for pearl millet, but the percentage overwintered plants was not affected by the cutting interval. Thus, the combination of highest annual HDMY and highest overwintering ability was attained by cutting at a 90-day interval at a 30-cm height in kinggrass.

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Six chlorophyll meters (SPAD) were compared to determine the magnitude of differences in SPAD readings on rice leaves. Correlations among the six SPAD meters were statistically significant (P<0.01) with correlation coefficients (r) ranging from 0.971 to 0.990. However, the differences in SPAD readings were statistically significant among the six meters (P<0.05) and the difference between two meters was as large as 2.7 units. Such magnitudes of discrepancy should be considered when different SPAD meters are used in the same study.

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