Soybean redistributes or"mobilizes"a large amount of its vegetative nitrogen in support of synthesis of seed storage protein. Most of this is from leaf tissue. Our objective was to elucidate the relationship between potentially mobilizable leaf nitrogen and seed yielding capacity of soybean. In each of two years, we grew 63 diverse soybean genotypes in a replicated field experiment. Whole plants were harvested from 1 m² of plot area. Leaf mass, leaf area index, and leaf nitrogen concentration were determined at beginning of seed growth (R5). Seed yield was obtained by combine harvest. Seed yields ranged from 2400 to 4400 kg ha^-1 the first year and from 2200 to 3800 kg ha^-1 the second. Total leaf nitrogen content at beginning of seed growth, after adjustment for differences in reproductive duration and lodging, accourited for 40 and 34% of genotypic variation in seed yield for the two years. Leaf mass, leaf area index, and leaf nitrogen concentration were less well related to yield. Reproductive duration, estimated as the time from beginning bloom to maturation, accounted for 30 and 20% of genotypic variation in seed yield, and lodging accounted for 21 and 23% for the two years. The three most important factors, total leaf nitrogen content at R5, reproductive duration, and lodging, as determined by multiple regression, accounted for 64 and 59% of genotypic variation in yield the two years. Hypothetical selection for total leaf nitrogen content at beginning of seed growth revealed a lack of consistency in genotypic performance between years, suggesting low heritability of the trait and therefore a low probability for improving the trait through plant breeding. We conclude that the failure of genotypes to perform similarly between years implies that the vegetative nitrogen pool is a very important, albeit secondary, source that is drawn upon variably in different environments depending upon the plant's capacity to assimilate nitrogen directly.

View full abstract

Summer field crop plants in Japan would develop large shoots but poor root systems during the rainy season called "Baiu". This might have adverse effects on dry matter production in summer thereafter even when they grow under sufficient soil moisture conditions. The effects of pre-flowering soil moisture conditions on dry matter production and ecophysiological characteristics were investigated. Soybean plants were grown under sufficient (W plot) and deficient (D plot) soil moisture before flowering in the field. Under sufficient soil moisture conditions after flowering, the plants in the D plot produced higher dry matter due to higher net assimilation rate (NAR) and higher grain yield due to higher pod-flower set ratio and a heavier seed than in the W plot. The higher NAR in the D plot was attributed to (1) a lower resistance to water transport in plants, which is necessary to maintain a high leaf water potential and high photosynthetic rate during the daytime and (2) delayed senescence. The plants in the D plot had a well developed root system, and had roots with high physiological activity represented by a large amount of exudation from the basal cut end of the stem. The development of physiological activity of the root system maybe reflected in higher capacity of root functions, the higher pod-flower set ratio and the delay in the senescence. Improved cultivation practices such as drainage during the rainy season and breeding of the plants with well-developed root system during the rainy season may be necessary to increase the yield of summer crops in Japan. Irrigation during the summer may not be so effective for the plants with a poorly developed root system.

View full abstract

The differences of flowering habit, yield and yield components between determinate (cultivar Tatisuzunari) and indeterminate (cultivar Touzan 69) soybean were examined in relation to raceme order. Although flowering habit, i.e., successive flowering from basal to apical nodes was the same in both types, the succession of flowering on low order racemes on the main stem increased more rapidly (1.4 nodes per day) in Tatisuzunari than in Touzan 69 (0.8 nodes per day). In Tatisuzunari flowering on a higher order raceme began after flowering of the first order raceme had finished, but in Touzan 69 flowering on the first order raceme continued upto higher nodes accompanied with flowering on higher order racemes thus producing a higher number of flowers. In Tatisuzunari, the flower shedding rate was higher, the higher was the raceme order, but in Touzan 69 the shedding rate was highest in the first and second order racemes. The pod setting ratio on all racemes was higher in Tatisuzunari than in Touzan 69. In Tatisuzunari, the 100 seed weight was similar on every raceme, although that on the second order racemes with compound leaves was slightly higher. In Touzan 69, it decreased with the increase of raceme order. The second order raceme with compound leaves played a pivotal role for the determination of total number of nodes, number of flowers, pod setting ratio, number of pods per plant and 100 seed weight in Tatisuzunari. However, in Touzan 69, racemes contributing to yield were limited to the first and second racemes. In Touzan 69, leaf length decreased drastically from basal to apical nodes, favoring the even distribution of light in the canopy, whereas, in Tatisuzunari, the leaf length increased from lower to higher nodes.

View full abstract

A new non-destructive method for the measurement of root elongation in soil was developed using acoustic emission (AE) sensors. Collisions between soil particles caused by the growth of the root tip generated sound pulses that were detected by the AE sensors. In a simulation experiment, using a stainless steel rod (d=1.3 mm), AE counts increased as the rod approached the sensor. The relative AE count (Ri) calculated from the values obtained from two sensors, vertically placed 15 mm apart, was only slightly influenced by the rod penetration rate and soil conditions, and linearly correlated with the distance between the rod tip and the center of the upper AE sensor. In the experiments using a maize primary root, Ri (Y) was significantly correlated with the distance (X) between the root tip and the center of the upper AE sensor as in the simulation experiment. Accordingly the root tip position could be estimated using the equation Y=0.994-0.0640X (r=0.883^**) . Calculated values for root elongation were comparable to those obtained from actual measurements.

View full abstract

Spatial and temporal variations of photosynthetic photon flux density (PFD) measured using small photodiodes (Hamamatsu, model G1118) attached on the leaf surface of rice (Oryza sativa L.) differed with the orientation and inclination even at the same height of the canopy. Under sunny conditions, the fluctuation pattern of PFD was mainly determined by the orientation and inclination of the leaf surface, and not by the daily change of PFD in the open, e. g., high peaks of PFD were observed in the morning on east-oriented leaves, but only low peaks on north-oriented leaves. Under overcast conditions, however, the PFD on the leaf surface depended highly on the PFD in the open irrespective of the leaf orientation and inclination. The present study suggests that the orientation and inclination should be considered as the major factors influencing the PFD regime (spatial variation and daily total PFD) within the rice canopy. To determine the effects of spatial and temporal variations of PFD on crop productivity, the daily net assimilation of each leaf was estimated from the obtained data and the light-photosynthesis curve.

View full abstract

Field experiments were conducted to characterize intercropping advantages in groundnut-fingermillet intercrop in relation to crop combination ratios, soil moisture and nitrogen (N) availability. Three intercrops in 1:2, 1:1 and 2:1 alternating rows of groundnut and fingermillet were examined for their growth and yield in comparison with their respective sole crops in 1996. The effect of well watered (W) and water stressed (D) conditions on the intercropping advantage was also examined for 1:1 intercrops in 1995 and 1996. Fertilizer N was applied at the rate of 20 kg ha^-1 in 1995 and 50 kg ha^-1 in 1996. The total above-ground biomass (DM) and its land equivalent ratio (LER) were highest in the 1:1 combination ratio. The DM production of intercropped fingermillet was higher in 1996 with higher N than in 1995 with low N application, while those of groundnut were similar in both years. The intercropped ground, nut exhibited significantly higher DM production after the fingermillet harvest. The LERs in grain yield were higher in l996 (1.43 under W and 1.45 under D), than in 1995 (0.87 under W and 1.22 under D). Also, LERs were consistently higher under D than W conditions. Water stress severely reduced the leaf area index (LAI) of fingermillet at a low N, especially in the later stages, whereas higher N alleviated the water stress effect. A close linear relationship was observed between LAI and leaf area (LA) per unit leaf N both for groundnut and fingermillet, with intercrops producing larger LA per unit leaf N than sole crops. Intercropping maintained higher ability in leaf net photosynthesis and transpiration of groundnut up to later stages, and significantly reduced water evaporation from the soil surface under the canopy than sole cropping of fingermillet. These results suggest that three processes associated with the intercropping yield advantages in the groundnut-fingermillet intercrop;1) higher leaf photosynthesis and vigorous growth of groundnut after the fingermillet harvest, 2) higher LA production per unit N and 3) efficient water use. In conclusion, interspecific shading was considered to be the key mechanism associated with these processes, leading to the intercropping advantages. The degree of the interspecific shade and its effect on growth and yield depended on the available soil N and water.

View full abstract

One cycle of selection was applied for studying genetic gain and heritability of seedling characters such as shoot length and root length at a low temperature in two genetic populations. The correlation of these characters to yield components was also examined. Selection had a significant effect on seedling characters other than shoot-root ratio. Selection for a long shoot or root increased the percentage of germination, shoot length, root length, panicle length and panicle weight in the field. Shoot length was significantly correlated to root length. There was a relationship between seedling characters and yield components. A genetic gain for seedling characters was obtained. Shoot and root lengths are heritable characters and may be useful as selection criteria at low temperatures. Heritability differed with the population selected for shoot or root length. Heritability values were 0.28∼0.69 for shoot length and 0.37∼0.76 for root length. Further selection gain for a longer shoot and root should be possible.

View full abstract

Pearl millet (Pennisetum typhoideum Rich.) was selected for yield and yield components. Sub-populations selected for high value of grain yield, seed weight, panicle weight and productive panicles showed higher values of the selected characters than those selected for low values and the original population. The genetic gains were obtained and heritability values were estimated as 0.74, 0.84, 0.65 and 0.50 for yield, seed weight, panicle weight and productive panicles, respectively. Genetic correlations between the yield and seed weight, panicle weight and productive panicles were calculated as 1.00, 0.89 and 0.75, respectively. Indirect selection for yield components improved grain yield. Grain yield was between 371 and 590 g m^-2. Accordingly, selection for yield components may be effective for improving grain yield.

View full abstract

The number of grains per spikelet and the number of spikelets per spike are important factors that influence grain yield in wheat. Three wheat genotypes in four foreign groups (OA, OC, OH and OJ) differing in spike type and Japanese cultivars (cvs) were grown under various combinations of seeding densities and fertilization levels. In all groups, the spikelet number per spike and the spike length at maturity were highest at low seeding densities and high levels of fertilization. The OA group (Nepal) and Haruyutaka (Japanese cv) gave a weak response in spikelet number per spike, while the OJ group (Xinjiang Uygur, China) gave a weak response in spike length. The OC group (except for T6), the OH group (Tibet) and Japanese cvs (except for Haruyutaka) responded to treatments in both spikelet number per spike and spike length. The T6 genotype in the OC group (Nepal) gave a weak response in both spikelet number per spike and spike length. Although the OA group had the longest spikes and the OJ group had the shortest spikes, there was no difference in the duration of spike elongation between the OA group and the OJ group. Spike length appeared to be determined mainly by the rate of spike elongation and was not restricted by the dry weight of the spike during the growth phase of the spike.

View full abstract

The grain shattering habit was examined in nine common buckwheat cultivars/strains (Fagopyrum esculentum Moench.) and four tartary buckwheat strains (F. tataricum Gaertner). As indices of grain shattering habit, the breaking bending strength and breaking tensile strength of the pedicel and the pedicel diameter were measured. Thin longitudinal pedicel sections were also observed. The breaking strength showed significant differences among cultivars, but the stage of seed maturity influenced the grain shattering habit. The two breaking strengths were larger in common buckwheat than in tartary buckwheat, and these differences may be explained by the pedicel diameter. The abscission layer was not observed in the pedicel tissue of the buckwheat cultivars.

View full abstract

This paper describes the ultrastructure of the electric field-induced fusion products of C₃ and C₄ species of Amaranthaceae at the early developmental stage. Protoplasts of C₃ species were isolated from a Celosia cristata L. cell suspension and, those of C₄ species were isolated from an Amaranthus tricolor L. cotyledon. Incompatibility occurred in the C₃/C₄ hybrid. The incompatibility reactions were detected in the newly formed hybrid cells accompanied with significant changes in the nucleolus (segregation of nucleolar components) and plastids (cup-like shape or amoeboid plastid enclosing cytoplasmic materials) of C₃ species parent. The structural changes in the organelles of the C₄ partner were less marked. After 5 days of culture, most organelles showed high cellular activity, and a normal dedifferentiation process of mesophyll chloroplasts was observed. At this stage nucleolar segregation was not detected and the C₃ Species plastids were difficult to distinguish from the proplastids formed from mesophyll chloroplasts. In addition, some mitochondria showed bursting-like structure. However, under the culture condition used these somatic incompatibility did not seem to impair further growth of fusion products since they were still proliferating well resulting in callus formation.

View full abstract

Drought is a major production constraint of rainfed lowland rice grown in Thailand and Laos. Adverse soil conditions also reduce yield. In an attempt to increase rainfed lowland rice production in these countries, a major collaborative international project was conducted during a 6-year period in the region. The objectives of the project were to quantify production constraints, determine genotypic variation in yield, and identify an effective breeding strategy. A rice simulation model was developed also and used to investigate the potential impact of strategies for genetic improvement and agronomic management. Four major physical or biological constraints to higher production levels of rainfed lowland rice were identified, (1) the lack of standing water at the appropriate time of transplanting, (2) severe water stress that often develops at the end of the growing season, (3) low yield potential of the present cultivars, particularly in Thailand, and (4) adverse soil conditions including low pH and low soil fertility. The results of the field experiments and simulation modelling exercises showed that the influence of these constraints can be reduced and yield increased by several methods:in particular, choice of appropriate cultivars and time of sowing to match crop phenology with water availability, application of appropriate fertilizer, adoption of high yielding cultivars, adoption of direct seeding in place of the traditional transplanting system, and reduction of percolation water loss from the paddies. A technology package currently being investigated for the rainfed lowland rice is direct seeding early in the season, using cultivars that flower by the end of the rainy season, with application of organic or chemical fertilizer. The appropriate cultivars are early flowering and short-intermediate statured, possess high yield potential and ability to maintain favourable plant water status at flowering, and have the ability to establish well and compete against weed under direct seeding.

View full abstract