Motoki Takahashi

Characteristics of Growth and Yield Formation in the Improved Genotype of Supernodulating Soybean (Glycine max L. Merr.)

Abstract Most of the supernodulating soybean lines were agronomically inferior to conventional genotypes. Our previous tests with ‘En6500’, a supernodulating mutant derived from a variety ‘Enrei’, revealed that its low growth and yield were not necessarily due to supernodulation. In our attempts to improve the yield of En6500 through crossing with Enrei, we recently succeeded in selecting a supernodulating line showing vigorous growth. Field experiments with this new supernodulating line ‘En-bO-1-2’ for three years revealed that it yielded much more than En6500. When the overall yield level was low, it even tended to yield more than Enrei. En-bO-1-2 thus showed a remarkably higher productivity than other supernodulating lines reported so far. Its improved yield was largely due to : (a) better seed filling, (b) vigorous vegetative growth during flowering period, and (c) high leaf area index and leaf N content that enabled production of more photosynthates to enhance N fixation and dry matter accumulation during the period of pod and seed development.

Characterization of Vegetative Growth of a Supernodulating Soybean Genotype, Sakukei 4

Article 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 thevegetative 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.

Characterization of nitrogen assimilation in a supernodulating soybean mutant En6500

Abstract A supernodulating and nitrate-tolerant soybean (Glycine max (L.) Merr.) mutant En6500 and its wild-type parent, cv. Enrei were cultured hydroponically at various nitrate (KNO3) levels (0.5, 5.0, and 15.0 mol m-3) to analyze the characteristics of nitrogen fixation, nitrate absorption, and associated characters in this mutant. The mutant produced a larger number of nodules, higher nodule dry weight, and a larger amount of fixed nitrogen per plant, thus depending more on fixed nitrogen at all nitrate levels than its parent. The mutant also exhibited a nitrate tolerance in nodule number and nodule dry matter, though the amount of fixed nitrogen per plant or on a nodule dry weight basis was reduced with increasing nitrate levels. The ability of nitrate absorption and plant growth in the mutant were inherently less active than those of the parent even in the absence of inoculation (non-nodulating conditions). Inoculation enhanced the low performance of nitrate absorption and growth in the mutant, whic...

Growth and Yield Responses of Two Soybean Cultivars Grown under Controlled Groundwater Level in Southwestern Japan

Abstract One of the limiting factors of soybean yield in southwestern Japan is soil moisture fluctuation from flooding to drought. The Farm-Oriented Enhancing Aquatic System (FOEAS), which consists of underdrain and sub-irrigation systems and can keep groundwater levels stable, was developed in 2005 to solve this problem. To obtain basic information on soybean cultivation using the FOEAS in southwestern Japan, we examined the growth response to groundwater level by using two cultivars (cv. Fukuyutaka and Sachiyutaka) in 2008 and 2010. Plant growth, yield, yield components and seed components (protein and oil contents) were analyzed. We also studied the effect of sowing time (normal or late). The groundwater level was controlled at depths of 20 and 35 cm or not treated (NT) as a control. The groundwater level could be kept at the target depths (20 and 35 cm) by FOEAS throughout the experimental period, but that in the NT plot fluctuated greatly. The growth and yield of Sachiyutaka might be increased by FOEAS, especially in late sowing, but the yield of normal sown Sachiyutaka was decreased in the 20-cm plot in 2010. Yield of late-sown Fukuyutaka tended to be decreased in the 20-cm plot. These results suggest that (1) the optimum groundwater level for yield of Sachiyutaka is between 20 and 35 cm, regardless of sowing time and (2) the groundwater level should not be kept at 20 cm for late-sown Fukuyutaka. Further studies are needed to determine the optimum groundwater level for each cultivar.

Responses of a Supernodulating Soybean Genotype, Sakukei 4 to Nitrogen Fertilizer

Abstract The supernodulating soybean genotype Sakukei 4 is potentially high-yielding. We characterized its leaf nitrogen (N) content, photosynthesis and growth at different developmental stages and under different dosages and types of N fertilizer, and compared it with its parental cultivar Enrei and the non-nodulating line En 1282. At the pod -expansion and seed-filling stages, the N contents per leaf dry weight and per leaf area, and apparent photosynthetic rates (AP) were higher in Sakukei 4 than in the normal and the non-nodulating genotypes. The nodule activity per plant was also higher in Sakukei 4 than in Enrei during the reproductive stage. These traits varied less with the growing condition (field- or pot-grown) and dose or type of N fertilizer applied in Sakukei 4 than in the other genotypes. The superior ability of Sakukei 4 to maintain high leaf N and AP, however, did not enhance its growth performance, which tended to be inferior to that of Enrei. Further studies are needed to define the cultivation conditions optimal for an exploitation of the favorable traits of Sakukei 4.

Effects of Cutting Height and Trampling over Stubbles of the First Crop on Dry Matter Yield in Twice Harvesting of Forage Rice

Abstract We examined the effects of cutting height and trampling over stubbles of the first crop on dry matter yield in twice harvesting of forage rice Oryza sativa L., Tachiaoba and Taporuri. Dry matter yield of the second crop, after the first harvest at the full-heading stage, increased with increasing cutting height. However, the dry matter yield of the first crop decreased with increasing cutting height. Overall, total dry matter yield did not vary with the cutting height. Dry matter yield and its components of the second crop were not greatly affected by the trampling treatment. At cutting heights of 15 and 5 cm from the base, the number of tillers developed from unelongated nodes was increased by the trampling treatment. Thus, although the number of tillers developed from the elongated nodes was decreased after the trampling treatment, the decrease is compensated for by the increased number of tillers from unelongated nodes.

Characteristics of Nodulation and Nitrogen Fixation in the Improved Supernodulating Soybean (Glycine max L. Merr.) Cultivar ‘Sakukei 4’

Abstract Supernodulating soybean lines have more than several times as many nodules as normal cultivars. They are expected to have high nitrogen-fixing ability and enhanced productivity, but their yields have been inferior to those of normal genotypes. We have recently developed a new supernodulating cultivar,‘Sakukei 4’(formerly ‘En-b0-1-2’, presently‘Kanto 100’), with improved growth and yield. The objective of the present study was to identify the characteristics of the nodulation and nitrogen-fixing ability of Sakukei 4. In pot trials, the nodule number of Sakukei 4 was 8.3 times that of a normal cultivar,‘Enrei’, and the nodule weight per plant was 2.3 to 2.8 times the value for Enrei. The acetylene reduction activity per plant in Sakukei 4 was higher than that in Enrei and conventional supernodulating genotypes, especially during the late growth stage. Compared with conventional supernodulating lines, the improved vegetative growth in shoots and roots of Sakukei 4, especially after flowering, probably enhanced its nitrogen-fixing ability per plant. We consider that its high nitrogen-fixing ability at the seed-filling stage, would help increase its yield in fields with low nitrogen fertility.

Plant Nitrogen Levels and Photosynthesis in the Supernodulating Soybean (Glycine max L. Merr.) Cultivar ‘Sakukei 4’

Abstract Supernodulating soybeans, having several times more nodules than normal genotypes, are expected to produce higher dry matter and grain yields through a higher nitrogen fixation potential. However, their growth and yield have been inferior to those of normal genotypes. We have recently developed the supernodulating genotype‘Sakukei 4’(formerly‘En-b0-1-2’, presently‘Kanto 100’), with improved growth and yield and a high nitrogen fixation potential. The objective of the present study was to examine the time course of changes in plant nitrogen content, leaf chlorophyll content (SPAD value), and photosynthetic rate of Sakukei 4 to reveal the source of its advantages in growth. The leaf nitrogen content after the flowering stage and the stem nitrogen content after the seed-filling stage were higher in Sakukei 4 than in the normal cultivar‘Enrei’. The SPAD values in Enrei and another normal cultivar,‘Tamahomare’, decreased rapidly after the seed-filling stage, whereas that in Sakukei 4 stayed high until the late seed-filling stage. Differences in photosynthetic rate and leaf SPAD value between Sakukei 4 and Enrei were negligible at the beginning of podding but became very clear at the seed-filling stage because of the drop in the values for Enrei. In Sakukei 4, a large amount of nitrogen might not be translocated from leaf to seed during the seed-filling stage because of the higher capability of the nodules to send fixed nitrogen to the growing seeds. Sakukei 4 could thus maintain a high photosynthetic rate and grain growth during the seed-filling stage.