Rice sterility due to a high temperature at flowering is a serious agricultural problem that has been associated with global warming. The flowering stage in rice plants is most vulnerable to high temperature stress. Closed flowering rice plants may better withstand high temperature stress. The aim of this study was to determine the role of cleistogamy (closed flowering) in avoiding high temperature-induced sterility. Cleistogamy was induced by moderate heat treatment at 30ºC during the panicle development stage. Both cleistogamous and chasmogamous (ordinary open flowering) rice plants, which possess the same genetic background, were subjected to 38ºC or 36ºC for 4 h just before flowering, and the percentage of fertility, number of pollen grains on a stigma, number of germinated pollen grains on a stigma, and temperatures inside and outside of the closed spikelets were examined. The cleistogamous rice plants showed a higher fertility percentage and a larger number of germinated pollen grains on a stigma than the chasmogamous rice plants. The temperature inside the closed flowering spikelets was 1.8ºC lower than that outside the spikelets. The cleistogamous rice plants thus showed avoidance to high temperature stress at 38ºC at flowering. On the basis of these results, we concluded that cleistogamy was advantageous to rice pollination and fertilization at high temperatures because of glume cooling.
Most of the existing studies regarding water-saving cultivation on rice are based on tillage rice, rather than no-tillage rice. The purpose of this study was to quantify the effects of nitrogen fertilizer on no-tillage rice cultivation under various soil moisture conditions, in order to determine the suitable soil moisture content for rice production by no-tillage cultivation. Pot experiments were conducted in the early seasons of 2010 and 2011. In each season, a hybrid rice cultivar, Jiyou716, was planted under the soil moisture contents of 95 – 100% (W100), 80 – 85% (W85) and 65 – 70% (W70). 15N was used as the nitrogen fertilizer. Yield, dry matter accumulation, nitrogen concentration and 15N abundance of maturity were determined for each sample. The nitrogen loss of basal N-fertilizer (BF) and tillering N-fertilizer (TF) in W70 was 22 – 24% and 18 – 45% larger than in W100, respectively, resulting in reduction in nitrogen uptake and total nitrogen accumulation in plants. The yield of rice by no-tillage in W70 was 47 – 42% lower in 2011 and 2010. There was no significant difference between W85 and W100 in yield, nitrogen uptake and utilization in no-tillage cultivation. It was concluded that the N uptake and yield were decreased by decreasing soil moisture contents to 70% of saturation in no-tillage cultivation. Soil content of around 85% was proposed as a suitable condition without a large reduction in the yield and N use in water-saving cultivation, although a field test is essential for practical use.
Quantitative trait loci (QTLs) affecting the shoot length and chlorophyll content of seedlings grown at a low temperature (16ºC) for 4 weeks were analyzed using inbred lines derived from a cross between an indica rice cultivar, Habataki, and a japonica rice cultivar, Arroz da Terra. Culm length of the inbred lines, measured at the harvesting stage, was also analyzed. The QTLs linked to increased shoot length (qSL1) and culm length (qCL1) on the Arroz da Terra allele were detected in the same region of chromosome 1, where the gibberellin 20 oxidase-2 gene (identical to Semi Dwarf1: SD1) located. Other QTLs (qSL3 and qSL8) that were linked to increased shoot length on Arroz da Terra and Habataki alleles, but had no effects on the culm length, were detected on chromosomes 3 and 8, respectively. The alleles of qSL3 and qSL8 might improve early shoot growth without increasing the risk of lodging caused by a long culm length. A novel QTL (qCC1) linked to increased chlorophyll content of seedlings grown at low temperatures through the effect of an Arroz da Terra allele was detected on chromosome 1, but it differed in position from the QTLs for shoot length.
Chloride (Cl) in saline soil increases the cadmium (Cd) concentration in crops. Here, we conducted a field experiment to investigate changes in Cd concentrations in wheat grain after the application of the Cl-containing fertilizer ammonium chloride (NH4Cl), with the aim of reducing its potential health risk. Effects of the application stage of NH4Cl fertilizer and leaching treatment (i.e., heavy rainfall) were also investigated in field and pot experiments. Both field and pot experiments showed that the Cd concentration of wheat grain was higher with NH4Cl fertilizer than with ammonium sulfate or urea fertilizers. Grain Cd concentration in wheat fertilized with NH4Cl at the tillering–jointing and flowering stages in the field experiment was 0.223 mg kg–1, which was about 1.5 times higher than that fertilized with urea. This finding is important because, in Japan, compound fertilizers containing NH4Cl are commonly used in fields for wheat cultivation. NH4Cl fertilizer application at the tillering–jointing and flowering stages had nearly equal effects on the Cd concentration in wheat grain. Basal dressing with NH4Cl fertilizer increased Cd concentrations in wheat grain to a greater extent than topdressing (at the tillering–jointing and flowering stage applications) in a pot experiment that was protected from rain. Leaching treatment (assuming two lots of 100 mm rainfall) negated the effect of NH4Cl fertilizer application on Cd concentration in wheat grain. We recommend the use of ammonium sulfate or urea preferentially as the nitrogen fertilizer because heavy rainfall rarely occurs during this period in Japan.
The germination and emergence of soybean [Glycine max (L.) Merr.] can be adversely affected by the presence of excessive water as a result of continuous rainfall. The pre-germination flooding-tolerant cultivars can be tolerant to hypoxia in the flooding field. The objective of this study was to clarify the relationship between germination under hypoxia at different temperatures and pre-germination flooding tolerance. Seeds of 6 soybean cultivars were subjected to 5 oxygen concentrations and 3 temperatures. Seeds of all 6 cultivars hardly germinated under an oxygen concentration of 20 mL L–1, but germinated with increasing oxygen concentration regardless of temperature. The pre-germination flooding-tolerant cultivar ‘Peking’ exhibited poorer germination under hypoxia than the other cultivars. Seed coat of ‘Peking’ did not dehisce when seeds did not germinate under hypoxia regardless of temperature. The pre-germination flooding-susceptible cultivar ‘Nakasennari’ exhibited higher seed coat dehiscence, but the dehiscence mostly occurred on the seed surface rather than micropyle under hypoxia at 25ºC and 30ºC. Seven days after termination of 3-d hypoxia treatment at 30ºC, the percentage of seedlings with root hairs and/or lateral roots relative to that after ambient oxygen treatment was maintained in ‘Peking’ but decreased in the other cultivars, especially in ‘Nakasennari’. Pre-germination flooding-tolerant cultivar, especially ‘Peking’, is characterized by a delay in germination processes under hypoxia, and exhibits vigorous germination after release from hypoxia.
Extracellular ATP (eATP) can function as a signaling molecule to regulate a wide range of cellular processes. We investigated the regulatory role of eATP in the cell death induced by salicylic acid (SA) in suspension-cultured tobacco (Nicotiana tabacum L.) cells. Treatment of tobacco suspension cells with SA induced cell death. The same treatment lowered the levels of eATP, accompanied by a decrease of both the respiratory O2 uptake and intracellular ATP levels in tobacco suspension cells. Treatment with β,γ-methyleneadenosine 5’-triphosphate (AMP-PCP), which is the non-hydrolysable analogue of ATP and can exclude eATP from binding sites of eATP receptors, also induced cell death in tobacco cell cultures. Treatment with exogenous ATP partially alleviated the cell death induced by SA. These observations suggest that eATP is involved in the SA-induced cell death in tobacco cell cultures.
In Japan, soybeans are generally cultivated in paddy fields which often have poor drainage. West of the Kanto region, the seeds are sown in the rainy season. Therefore, the seedling establishment is prone to damage by the rain after sowing. The generation of sulfide ions in flooded and reduced soil is thought to be one factor causing this flooding damage. Since molybdate ions suppress the generation of sulfide ions, the effect of coating soybean seeds with molybdenum compounds, on the seedling establishment under a flooded condition was examined. Soybean seeds were coated with several kinds of poorly-soluble molybdenum compounds at different concentrations. The coated seeds were sown in soil and then flooded for 3 d at 25 – 30ºC. Seedlings were not established from seeds not coated with molybdenum compounds. Seedling establishment was appreciably improved by coating the seeds with a molybdenum compound at the rate of 0.5 – 1 mol-Mo kg–1 seed. Seedling establishment was especially improved by coating with molybdenum trioxide. Accordingly, coating the soybean seed with molybdenum compounds could mitigate the flooding damage occurring after sowing.
Green stem disorder (GSD) of soybean reduces harvesting efficiency and negatively impacts seed appearance when mechanical harvesting is employed. Two recombinant inbred populations were investigated for the effects of segregating stem determination and flowering time on GSD at two different locations, Kyoto and Akita, over two years. Although the severity of GSD of each line varied considerably with the location, the scores showed significant correlation with the environment. Quantitative trait locus (QTL) analysis revealed a strong and consistent QTL for GSD severity in one population of recombinant inbred lines (RILs) across the environments at the Dt1 locus, which governs stem growth habits, and the determinate growth genotypes showed evident symptoms of GSD. However, QTLs were not detected near the Dt1 locus in the other population. Thus, it was unclear if the responsible gene was identical to the stem determination gene. The early flowering genotype showed a more severe symptom of GSD in both populations, but this effect was dependent on the allele at the Dt1 locus. The effect of another QTL detected in the latter population also depended on the allele at the Dt1 locus. Our results indicated that the genetic factor at the Dt1 locus and the factor controlling flowering time influenced the severity of GSD at each location and year and that their effects and interaction complicated the genetic control of the occurrence of GSD.
The characteristics of the relationship of natural 15N abundances (δ15N values) between rice and soil in organic farming and conventional farming were examined, and the possibility of discriminating organically grown rice from conventionally (non-organically) grown rice using this relationship was explored. Organically grown rice, conventionally grown rice and soil samples were collected from farmers’ fields in Daisen city and Yokote city, Akita prefecture, Japan as well as from the experimental fields of NARO Tohoku Agricultural Research Center located in Daisen from 2007 to 2009. Organic fertilizers and synthetic fertilizers available on the market in Akita prefecture were also collected. The δ15N values of those samples were measured. Regardless of the farming method, the δ15N values of rice reflected those of the soil. The δ15N values of the organic fertilizers available on the market were likely to be higher than those of the soil. Meanwhile the δ15N values of the synthetic fertilizers were negative and lower than those of the soil. The δ15N values of organically grown rice tended to be higher than the regression line obtained from the δ15N values of rice and soil without N source application. The δ15N values of conventionally grown rice tended to be lower than the regression line. These results indicated that the relationship of the δ15N values of rice and soil without an applied N source could aid in discriminating between organic rice and conventional rice.
Weeds are the most serious threat to crop production in organic farming systems. Information on the spatial distribution of weeds is important for effective weed management. The objective of this study was to evaluate the effect of the ground cover of the main crops (soybean and maize) and cover crop on the spatial distribution of weeds for two row sections, ‘within the row (IR)’ and ‘between the rows (BR)’. The cover crop was interseeded in BR 3 – 4 weeks after sowing the main crops in two years, and weed density and vegetation cover ratio (VCR, an index of ground cover) of the main crops and cover crop were measured. There was a significant difference in the spatial distribution of weeds between the two main crops. In IR, weed density was higher in maize than in soybean, while in BR, it was higher in soybean. This means that weed suppression in IR was more important for maize, while the suppression in BR was more important for soybean. The negative relationship between VCR of the main crop plus cover crop and weed density in each row section suggests that the difference in ground cover was one of the reasons for the difference in weed density between the two main crops. The cover crop markedly increased the VCR in BR, but only slightly increased VCR in IR in both main crops. These results suggest that the cover crop was more compatible with soybean than with maize, because the high weed density in IR of maize could not be decreased sufficiently by the slight increase of VCR in BR by the cover crop.
Crack fertilization is a soybean cultivation technique for nodulation control in which midterm subsoiling is used to supply fertilizing materials to deep soil just before the flowering stage. This study examined the effects of fertilizing materials and the continuous application of nodulation control, on soybean yield enhancement in two field experiments. The survival of nodule bacteria in deep soil was also evaluated by a bioassay of nodule bacteria in a root box. When the nodule bacteria on biochar were continuously applied without any other chemical fertilizers for three successive years, seed weight was significantly heavier being up to 1.34 times that of the control. The application of nodulation control in the previous year but not in the experimental year did not have residual effects on seed weight. The enhancement of seed weight in a farm field converted from a paddy was much lower. This may be partly attributed to the midterm tillage practice, which destroys the crack structure after the nodulation control, together with soil water status and cultivar differences. Nodule growth and nitrogen fixation activities significantly increased in the soybean plants grown on the soil collected from the subsoil to which nodule bacteria on biochar had been applied the previous year. This suggests that nodule bacteria in the subsoil survived in the biochar habitat for at least a year after application. These results indicate that nodulation control by the crack fertilization technique leads to yield enhancement when nodule bacteria on biochar are continuously applied.
Because of the large amounts of starch accumulated in its trunk, the sago palm (Metroxylon sagu Rottb.) growing in tropical areas of Southeast Asia has received much attention as a starch crop mainly for use as an industrial raw material. Sago palm propagates generally by transplantation of suckers, but little agronomical knowledge is available for transplanted sucker growth. Our objectives are to clarify sago palm growth after transplantation and to assess the transition of stem growth from horizontal to vertical. The transplanted sucker stems elongate horizontally, creeping along the ground surface in the early growth stage. Subsequently, the stem elongation shifts gradually from horizontal to vertical. The creeping stem stands up, drawing a large arc and elongating vertically. The horizontal stem elongation stops at around 6.5 years after transplantation and the stem growth curve shows a sigmoidal curve. The stem growth stage of a transplanted sucker is divisible into three stages based on its elongation direction: the creeping growth stage, the trunk formation stage, and the trunk elongation stage. The creeping growth stage, which is the early growth stage after transplantation, is an important period because the standing positions of trunks are determined in the plant and in the sago palm garden. In the area we investigated, the transplanted suckers remained in the creeping growth stage for 4 – 5 years. They remained in the trunk formation stage for around 1.5 years. These suckers will probably be in a trunk elongation stage for 6 – 7-years.
Lodging is an important constraint limiting buckwheat yield and quality by bending or breaking culm on buckwheat production worldwide. This study was conducted with Ningqiao 01, a moderate lodging resistance cultivar of buckwheat, to determine whether lignin synthesis and lodging resistance of buckwheat are affected by nitrogen fertilizer and planting density. The results showed that the lignin content at the bottom of the 2nd internode was significantly and negatively correlated with lodging index and lodging percentage, but significantly and positively correlated with snapping resistance. The snapping resistance rose and then fell with the increase of nitrogen fertilizer. The snapping resistance decreased with the increase of planting density. The lodging index increased with the increase of nitrogen fertilizer and planting density. The lignin content and its related enzymes activities decreased with the increase of nitrogen fertilizer and planting density. These results suggested that the lignin content is closely related to the lodging resistance of buckwheat, and a higher lignin content could strengthen the lodging resistance of buckwheat. The increase of nitrogen fertilizer and planting density significantly increased the risk of lodging by decreasing the lignin content and its related enzymes activities at the bottom of the 2nd internode.
In recent years, water and labor shortage in Southeast Asia is driving the farmers towards dry-seeded rice systems. Weed infestation is a serious threat for adoption of these systems. A study was conducted in the wet and dry seasons to evaluate the performance of 10 elite “Green Super Rice” (a recently named group of rice genotypes bred for unfavorable marginal environments) genotypes at two different weed infestation levels (partial and moderate weed control) under dry-seeded conditions. Average yield loss due to weed competition in the partial weed control treatment ranged from 12 – 57% in the wet season and 2 – 23% in the dry season. In the partial weed control plots, the drought pyramiding genotype IR83140-B-11-B performed well, resulting in 2850 and 4610 kg ha–1 of yield in the wet and dry seasons, respectively. The yield loss of this genotype in the partial weed control plots relative to the moderate weed control plots was only 21% in the wet season and 10% in the dry season. Results clearly showed that grain yield in different genotypes were positively correlated with leaf area at an early stage of the crop. The study also found negative and linear correlation between grain yield and weed biomass at harvest, demonstrating the importance of weeds in dry-seeded rice systems. The study suggested that genotypes with a larger leaf area could be integrated with other weed management strategies to achieve sustainable weed control in dry-seeded rice systems.
Early maturity is an important trait for soybean [Glycine max (L.) Merr.] growing in Hokkaido where the growing period is restricted because of the short fall season and early snowfall. Development of an early-maturing line without decreased seed yield is difficult because of the positive correlation between days to maturity and seed yield. In this study, we developed two breeding lines, Tokei 1067 (T1067) and Toiku 251 (T251), that were derived from crosses between Japanese and Polish cultivars. T1067 and T251 had a significantly earlier maturing time than Yukihomare (YH), the standard cultivar in Hokkaido. The seed yield of T251 was similar to that of YH. Moreover, the chilling tolerance levels of the T1067 and T251 lines at the flowering stage were greater than the tolerance level of YH.
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