In North China, irrigation is required to obtain a high yield from winter wheat; this results in rapid aquifer depletion. The primary objective of this study was to investigate the influencing mechanisms of irrigation and straw mulching in preserving the soil moisture. Maize straw (3-5 cm) was mulched immediately after sowing winter wheat, and irrigation water was supplied at 60 mm, controlled by using a flow meter, during the jointing, heading, or milking stages of the crop. The results revealed that irrigation decreased the eddy thermal diffusivity, sensible heat flux, and soil heat flux, but increased the latent heat flux. In contrast, straw mulching enhanced the eddy thermal diffusivity and sensible heat flux, but decreased the latent heat flux. Straw mulching increased the soil temperature at 5 cm depth form January to February, but decreased the soil temperature before January and after February. There were no significant differences in the total evapotranspiration between mulched and non-mulched treatments, however, there was a statistically significant difference in the evapotranspiration among the different growing seasons. Straw mulching reduced the evapotranspiration from the seeding stage to the regrowing stage, and the evapotranspiration with mulching was less than that non-mulching 47.4 mm. Further, straw mulching significantly reduced the number of spikes in the crop. Both irrigation and straw mulching increased the number of kernels, but had no visible effects on the thousand kernel weight. These results indicate that straw mulching may decrease the yield and water use efficiency (WUE) of winter wheat in North China.
In this study, soil samples were collected from upland fields where maize and soybeans had been cultivated and the density of AM (arbuscular mycorrhizal) fungal spores and the percentage of soybean roots infected with AM fungi (infection ratio) were assessed to determine the factors of the soil chemical properties affecting the mycorrhizal infection. The roots and rhizosphere soil were sampled from 9 soybean fields and 8 maize fields in the summer of 2004. The soil samples were examined for chemical properties (pH, electric conductivity, total phosphate, available phosphate, and phosphate absorption coefficient) and the density of AM fungal spores. Soybean roots were stained with trypan blue to determine the infection ratio. There was a significant difference in soil pH and available phosphorus content with the sampling site. The phosphorus absorption coefficient markedly varied with the sampling site and there was a significant difference in the phosphorus absorption coefficient with the site. The spore density in the soybean and maize fields markedly differed with the sampling site and there was a significant difference spore density with the sampling site. The density of AM fungal spores in the soybean field was negatively correlated with the available phosphorus content, and showed a positive correlation with the phosphate adsorption. This means that an increase in the available soil phosphorus due to the application of phosphate fertilizers will lower the density of AM fungal spores in the soil and that the density of AM fungi spores is generally higher in soils with a higher phosphate absorption coefficient. It is considered that this tendency is marked in the soil with a low phosphate adsorption coefficient. The infection ratio was positively correlated with spore density, and negatively with the available phosphorus content. To increase mycorrhizal infection of soybeans, we need to decrease the amount of available soil phosphorus and simultaneously to increase the density of AM fungal spores. Excessive application of phosphorus fertilizers should be avoided.
The effects of day length and air temperature on the growth and flowering of sesame (Sesamum indicum L.) were examined to analyze the effect of seeding date on the seed yield. Short day (10-h light/14-h darkness) treatment decreased the final stem-length relative to natural day length (14.1—13.4-h), although it hardly affected the length of the stem-elongation period. The short-day treatment shortened the duration to the first flower and lowered the first flowering-node. It prolonged the flowering period, but decreased the flowering-node number on the main stem resulting from the slower rate of increase in nodes with flowers. Under a low day/night temperature condition (23/18°C), the stem growth was very slow and flowering did not occur. As compared with a high temperature (30/23°C), a low temperature (22/15°C) during 15 days after emergence suppressed the seedling growth temporarily, but the seedlings resumed growth after the temperature treatment. The growth and flowering behavior after the treatment were unaffected by a low temperature during the seedling stage. On the other hand, a low temperature during the flowering period decreased the flowering-node number resulting from the slower rate of increase in nodes with flowers, although it prolonged the flowering period. In this study, the decrease in the flowering-node number by short days and low temperature was smaller than that by delay of seeding date as observed in our previous study. Thus, the effects of day length and air temperature were not the sole factors responsible for the effect of seeding date on the flowering-node number.
In the afternoon when air humidity decreases, leaf photosynthetic rate (Pn) often declines in rice grown under irrigated conditions. To clarify the genotypic difference of Pn in response to humidity, we measured Pn and stomatal conductance (gs) for nine rice varieties with diverse genetic backgrounds, at various vapor pressure differences (VPD) and developmental stages. Pn and gs of all the varieties decreased with VPD increase from 1.0 to 2.3 kPa of VPD. The variety with high gs at low VPD exhibited a greater decline of gs with VPD increase than the variety with low gs, but cv. Takanari showed the highest gs under altered VPD conditions. Significant logarithmic relations were found between the decreased Pn and gs at the respective developmental stages, suggesting that gs is the dominant factor determining Pn and its response to VPD change. To explicate the effect of decreased gs on Pn, we analyzed the relations by using the model that accurately estimated the genotypic difference in Pn at a low VPD with gs and leaf nitrogen content per unit leaf area in the previous study. The model assuming that leaf internal conductance (gw) remains unchanged well explained the decreased Pn at high VPDs by gs change alone. The analysis also suggested the constancy of gw and carboxylation capacity at high VPD. It is concluded that the genotypic difference in the decrease of Pn at a high VPD is brought mainly by that in decreased gs, and the varieties with a high gs always exhibit a high Pn owing to their relatively high gs at either high or low VPD environments.
This study showed the effective microanalytic methods for detection of saikosaponin by a competitive enzyme-linked immunosorbent assay (ELISA) using anti-saikosaponin a (SSa) monoclonal antibody (MAb). The results showed that the competitive ELISA had higher sensitivity than high performance liquid chromatography (HPLC) for the detection of saikosaponin. ELISA showed a highly significant difference in SSa concentrations between the roots of Bupleurum falcatum with different origins. In addition, a difference in SSa concentrations was observed between cytologically different cultivars originating from Japan (2n=26) and Korea (2n=20). It also showed excellent performance in quantitative analysis of SSa in the small samples from regenerated plantlets and calli. In addition, Eastern blotting using anti-SSa MAb 3G10 multispecific to saikosaponins was applied to analyze the distribution of saikosaponins in Bupleurum falcatum roots and leaves. The localized distribution of saikosaponins in whole leaves and cork layer of the roots in B. falcatum was successfully demonstrated by this novel immunoassay.
In soybeans, increase in the dry weight of seed (IWS) during the seed-filling period (SFP) is nearly half that of the whole plant (IWP). Hence, the contributions of assimilate during SFP to seed growth in soybeans is apparently lower than that in other cereal crops. However, analysis of the assimilate budget for seed production based on dry matter could be misleading in soybeans because the carbon (C) contents of seed and that of other organs are different due to the differences in lipid and protein content and respiration loss in each organ results in underestimation of the C contribution to seed production. In field soybeans, irrespective of shading and thinning, IWS/IWP and harvest index (HIW) for dry weight were slightly lower than ICS/ICP and HIC for C, respectively. Of the 13C fed at the vegetative stage and early SFP, 3.4% and 16.4%, respectively were accumulated in the seed, 0.9% and 28.2%, respectively, in the pod shell and 26.8% and 37.8%, respectively were respired before maturity. Ninety-six percent of seed C was assimilated during the SFP. Respiratory loss of 13C fed at the early SFP was larger than that from 13C at the vegetative stage, showing that seed production requires much more C than leaf or stem growth. These results suggest that the difference in C contents between plant organs has little effect on the estimation of assimilate partition into soybean seeds based on dry matter, and high respiration loss for seed growth reduces the partition of dry matter into seeds.
The objective of this study was to clarify the effect of assimilate supply and high temperature on the occurrence of chalky kernels, i.e. milky white, white back, basal white and white belly kernels. Rice cultivars Koshihikari and Takanari, contrasting in number of spikelets in a panicle were used. After heading, sink-source manipulation was imposed on plants, through changing supply of assimilates to spikelets by shading or panicle clipping. Plants with each sink-source manipulation were subjected to temperature treatments, i.e., high temperature and ambient temperature, using a temperature-gradient chamber. Percentage of various types of chalky kernels was examined with the treatment for each cultivar. High temperature treatment increased milky white and white back kernels while no significant effect of temperature was observed on the percentage of white belly and basal white kernels. Effects of sink-source manipulation on the occurrence of chalky kernels varied with the type of chalky kernels. Although sink-source manipulation had no effect on white back and basal white kernels, it had a significant effect on the percentage of milky white and white belly kernels, which indicates the association of assimilate supply with the occurrence of these types of chalky kernels. A close hyperbolic relation was observed between the rate of assimilate supply and the percentage of milky white kernels, suggesting that milky white kernels are caused by assimilate deficit during the initial half period of grain filling. The higher percentage of milky white kernels at a given rate of assimilate supply at a high temperature implied that the high temperature during the grain-filling period increases the assimilate demand to avoid the occurrence of milky white kernels. This is presumably because the high temperature during the grain-filling period accelerates grain growth especially in inferior spikelets.
Hairy vetch (Vicia villosa Roth) has the potentials for preventing soil erosion and suppressing weed growth as a winter cover crop. We evaluated the additional N supplied by this crop harvested at different growing stages to the succeeding sorghum in pot experiments. Hairy vetch was grown in 1/5000a Wagner pot, and shoots (S) and roots (R) were mixed separately or together (S+R) into the soil on 30 March, 18 April and 2 May. After incorporation of the plants, seeds of sorghum were sown in the pots. Dry weight and N content of hairy vetch increased throughout the growing period. The value of nitrogenase activity in root nodules peaked on 18 April and then drastically declined. When hairy vetch was harvested on 30 March, N content of sorghum in the S pots was definitely less than that in the R and S+R pots. When hairy vetch harvested on 2 May, however, the N content in the S pots was similar to that in the S+R pots, and it was significantly higher than that in the R pots. Although N input from hairy vetch was higher in the S pots than in the R pots, N uptake by sorghum was not reflected in those values. The belowground parts of hairy vetch may have a considerable effect on N uptake of sorghum when using this plant species as green manures.
An F1 hybrid with the semi dwarf genes, Rht1 and Rht2, was crossed with Hordeum bulbosum and maize (teosinte) (bulbosum method and maize method) to produce doubled haploid (DH) lines, and 102 seedlings of each DH line produced by the two methods were treated with GA. The sensitivity to GA was shown by the GA index (GAI) which is (length of the first leaf sheath (LS) in GA-treated seedlings/length of LS in GA-untreated seedlings)×100. The scatter diagram of GAI plotted against culm length was divided into three groups, low, medium and high GAI groups. The segregation ratio of these gametophytic phenotypes was close to the expected ratio; 1:2:1=Rht1Rht2:(Rht1rht2+rht1Rht2):rht1rht2, in both DH lines produced by the two methods. The frequency distribution of culm length in DH3, DH4, DH5 and DH6 populations from DH produced by the bulbosum method showed two peaks, though that in F3, F4, F5 and F6 populations from the same F1 hybrid (non-selective population) showed a continual normal distribution. The ratio of individuals with a shorter culm length to those with a longer culm length in DH lines was close to the expected ratio; 1:3 [Rht1Rht2 : (Rht1rht2+rht1Rht2+rht1rht2)]. The frequency distribution of culm length in F6 was significantly different from that in F3-F5 populations, indicating an unintentional selection during the generation of the selfed hybrid, but the frequency of short culm relative to long culm individuals was lower in F3-F6 populations than in DH lines. These findings suggest the usefulness of selecting the medium culm-length lines in the DH lines produced by the bulbosum or maize method in addition to examining the GA sensitivity (GAI).
Waterlogging tolerance of tropical cordage fiber crops is an important agricultural subject in northeast Thailand, because they are often grown in dry-wet transition period as pre-rice crops. Since root anatomical characteristics are often considered to be important traits determining waterlogging tolerance of plants, we examined root anatomy of three fiber crops that are different in waterlogging tolerance one another. Seedlings of three cordage fiber crops, Hibiscus cannabinus (kenaf, cv. KhonKaen60), Hibiscus sabdariffa (roselle, Thai kenaf, cv. NonSoong2) and Corchorus olitorius (jute, cv. KhonKaen1), were grown in tall beakers of 1000 ml vermiculite with 40% v/v (control) and 80% v/v (waterlogging) water contents. It is known that the H. cannabinus cultivar is tolerant to waterlogging while other two species (C. olitorius, H. sabdariffa) cultivars are sensitive to waterlogging from soil-grown pot experiments in northeast Thailand. Ten days after sowing, freehand cross-sections of taproot (i.e., primary root) were made with 1 cm increments from the root tip along root axis followed by staining by toluidine blue O (0.01%) for light and fluorescence microscopy. Only H. cannabinus formed aerenchyma in cortex of the taproot under waterlogging condition. The aerenchyma of waterlogged H. cannabinus first appeared at 3 cm from the root tip and developed up to the base of taproot. The formation of aerenchyma in H. cannabinus roots may contribute to the waterlogging tolerance. Casparian bands were found in both endodermis and exodermis of taproot in all the three species. However, formation of exodermal Casparian bands was not stable, and they were restricted to the basal part of taproot in H. sabdariffa and C. olitorius. Waterlogging treatment suppressed formation of Casparian bands, particularly in exodermis.
The primary roots of eddo (Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehde) were treated with aluminum, and the localization of Casparian bands and crystal cells in relation to aluminum was investigated. The calcium oxalate crystal idioblasts (crystal cells) were localized at the peripheral parts of cortex between about 0.5mm and 6mm from the tip of primary roots. The crystal cells were arranged in tubular form, which is referred to as ‘tubular arrangement of crystal cells’. The Casparian band was apparently detected in the endodermis at 3mm from the root tip of primary roots treated with aluminum, under a fluoresence microscope with berberin hemi-sulfate. Aluminum was significantly stained with eriochrome cyanine in the root apical region of eddo after aluminum treatment. Not only in the periphery part of stele, but also the external part of the tubular arrangement of crystal cells was significantly stained. In addition, marked accumulation of aluminum stained with lumogallion was observed inside the crystal cells by z-staking observation with a confocal laser scanning microscope. The results suggested that Casparian bands in endodermis and the tubular arrangement of crystal cells obstructed the influx of aluminum into the inside of stele.
The contamination of cadmium (Cd) into the food chain can be harmful because Cd causes chronic health problems. To evaluate the breeding potential reducing the Cd concentration in wheat grain, we compared Cd concentrations in 237 wheat genotypes including Japanese landraces, Japanese cultivars and introduced alien cultivars for breeding using grain samples collected from upland fields in 2004-5 and 2005-6 growing seasons. The Cd concentration in wheat grain significantly varied with the growing seasons and with the experimental fields. Cultivars bred in northern Japan, including the recent Japanese leading cultivar ‘Hokushin’, tended to have a low Cd concentration in grain compared with that bred in central and southern Japan. Simple correlation analysis between Cd concentration in grain and agronomic characteristics revealed that the Cd concentration in grain showed significant negative correlations with stem number, culm length and spikelet number per spike, and showed significant positive correlation with SPAD value (chlorophyll content) of flag leaf. Stepwise multiple-regression analysis showed that the genotypic variation of Cd concentration in grain was associated with the culm length and spiklet number per spike. This study clarified the geographical pattern of genotypes with different Cd concentrations in grain in Japanese wheat cultivars. Cultivars originating from northern Japan may be useful genetic resources to develop cultivars with a low Cd concentration in grain to be grown in the areas where Cd accumulation in wheat grain is a problem.
A study was conducted in Bajgah (deep water table condition) and Kooshkak (shallow water condition) areas in Fars province in I.R. of Iran to investigate the effects of different nitrogen application rates, deficient irrigation by alternate furrow irrigation (AFI) method and their interaction on the yield and water- and nitrogen use efficiency of winter wheat. The experimental design was split plot with three main plots as irrigation treatments [ordinary furrow irrigation (OFI), fixed alternate furrow irrigation (FAFI) and variable alternate furrow irrigation (VAFI)] and four subplots as nitrogen application rates (0, 90, 180 and 270 kg ha-1) repeated three times. The amount of irrigation water for each irrigation event was considered equal to readily available water of soil in the root zone, and the time of irrigation was determined by the cumulative evapotranspiration (according to Penman-FAO method). The total amounts of irrigation water were 439.0 and 256 mm for OFI and AFI, respectively in the Bajgah area, and 367 and 226 mm, respectively, in the Kooshkak area. Total seasonal rainfalls were 409.0 and 470.5 mm in the Bajgah and Kooshkak, respectively. The results indicated that the interaction between irrigation method and nitrogen application rate was statistically significant for total biomass but not for grain yield and other traits. In terms of grain production, VAFI was superior to FAFI in the Bajgah and Kooshkak areas. VFAI in Bajgah and Kooshkak resulted in 42 and 39% reduction in irrigation water use and 22 and 13% reduction in grain yield, respectively, compared with OFI. Based on the grain yield, nitrogen use efficiency, apparent nitrogen recovery and water use efficiency, it was concluded that VAFI with application of 180 kg N ha-1 is appropriate in the experimental areas. Based on the grain yield and protein content, VAFI with application of 270 kg N ha-1 was also appropriate due to 21-35% greater production of total protein, although nitrogen use efficiency, and apparent nitrogen recovery decreased by 20 and 16%, respectively, compared with 180 N ha-1. Further, water-use efficiency in VAFI with 180 kg N ha-1 was 0.89 and 0.85 kg m-3 in the Bajgah and Kooshkak areas, respectively, which were values not significantly different from those obtained in VAFI with a nitrogen application rate of 270 kg ha-1. Therefore, VAFI with a nitrogen application rate of 180 kg ha-1 is a recommendable practice in the study areas.
Aggregate sheath spot (AgSS), a disease caused by Rhizoctonia oryzae-sativae, is one of the major rice (Oryza sativa L.) diseases in California. A three year study was initiated in 1998 to evaluate the effect of nitrogen (N) and potassium (K) fertility on the severity of AgSS. A field with a history of AgSS was divided in two: in one the straw was incorporated and in the other the straw was removed. Rice was fertilized annually with five rates of N ranging from 0 to 200kg ha-1 (main plot) and six rates of K ranging from 0 to 125kg ha-1 (sub-plot). Soil K levels in both fields declined over time and by the third year, soil K was below the critical level of 60μg K g-1 soil in both fields. There was a grain yield response to K fertilizer in all 3 years in the field where straw was removed and in the third year when straw was incorporated. Where there was a significant response to K fertilization, yields increased by 560kg ha-1. In all fields and years there was a significant yield response to N fertilizer. AgSS severity decreased with increasing N and K fertilizer rates and leaf N and K concentrations at panicle initiation. Furthermore, the leaf N concentration required for maximum rice yields was lower than the leaf N concentration which resulted in the lowest severity of AgSS.