Aerobic culture is a water-saving technique for direct-seeded rice cultivation. Growing rice under continuously unsaturated soil conditions can maximize water-use efficiency and minimize both labor requirements and greenhouse-gas emissions. Under a temperate climate, aerobic culture can produce a rice yield greater than 9 t ha-1 especially in central Japan (11.4 t ha-1). Aerobic culture using large-scale center-pivot sprinklers is being established in the central United States, where yields can surpass 10 t ha-1. However, yields remain at less than 8 t ha-1 in the tropics. The high yield of Japanese aerobic culture is mainly attributed to vigorous nitrogen uptake during the reproductive stage, which allows rice plants to produce more spikelets and biomass. Fertilizer management for aerobic culture must satisfy both the nitrogen demand and control spikelet density to achieve an appropriate sink-source balance. Unfortunately, the poor development of the root system in rice limits its water uptake from unsaturated soil. Adaptive responses such as adventitious root emergence, lateral root branching, and deep root penetration would protect the plants against dehydration stress in aerobic culture. Intermediate plant height with a few large tillers rather than semi-dwarf stature with profuse tillering should be a suitable plant type for aerobic culture, and plants should show leaf expansion despite fluctuations of soil moisture. The development and identification of suitable genotypes and crop management options are underway worldwide for more resource-use efficient and productive aerobic rice culture.
Morphological changes and function of calcium oxalate crystals in eddo roots in hydroponic solution containing calcium at various concentrations were investigated. Bundles of needle-shaped crystals in crystal idioblasts were tubularly arranged in the peripheral part of cortex in the apical zone of primary roots. Under scanning electron microscopy and optical microscopy, crystals in the idioblasts of roots cultured in 1 mM calcium nitrate solution were larger than those in 0 mM calcium solution but smaller than those in the solutions containing either 15 mM calcium nitrate or 15 mM calcium chloride. The number and area of crystal bundles in the sections of the apical zone in 1 mM calcium nitrate solution were significantly larger than those in 0 mM calcium solution and smaller than those in the solutions containing 15 mM calcium. The calcium mapping image obtained by energy dispersive X-ray spectrometry showed that the amount of calcium in crystal idioblasts was increased with increasing calcium concentration in the solutions. However, the weight percentage of calcium per cortex parenchyma cell in root apical zone did not vary significantly with the concentration of calcium in the solutions. In the root zone apart from the root apex having no crystals, the weight percentage of calcium per cortex parenchyma cell in the solutions containing 15 mM calcium was significantly higher than that in either 0 mM calcium or 1 mM calcium nitrate solution. These results suggested that the crystals in the tubular arrangement participated in the regulation of calcium levels in the apical zone of primary roots.
Both saline and alkaline stresses involve osmotic stress and ion injury; however, alkaline stress involves the stress due to a high pH. The aim of this study was to evaluate the physiological responses of linseed seeds and seedlings to saline and alkaline stresses and to elucidate the adaptive mechanisms involved. Stresses were generated by exposure to neutral saline solutions of saline stress and alkaline stress for 7 days. The relative growth rate (RGR) and water content (WC) of linseed seedlings were scarcely affected by salinity stress, but significantly reduced by alkaline stress. Photosynthetic activity and pigment indices were hardly changed under saline stress but were inhibited by alkaline stress. This implies that alkaline stress may be mediated by Na+ uptake and accumulation up to toxic levels, leading to a decrease in photosynthetic pigments and damage to the photosynthetic apparatus. Alkaline stress causes precipitation of phosphate and metal ions which causes a sharp decrease in ionic activity and in the concentrations of various other ions. The results indicated that carbohydrates and proline synthesis decreased osmotic potential, remedied the shortage of inorganic anions and maintained stability of the intracellular pH allowing the plant to cope with osmotic stress from a high Na+ vacuolar concentrations. However, the contribution of betaine to osmotic adjustment was small in linseed seedlings. With increasing solution concentrations, the rate of germination of linseeds was more severely inhibited under alkaline stress than under saline stress.
Salinity stress causes various physiological dysfunctions in soybean (Glycine max (L.) Merr.). For example, reduced nitrogen (N) uptake due to salt-induced depression of nodule formation severely limits soybean growth and yield. Super-nodulating soybean genotypes were previously identified by their superior N2 fixation and photosynthesis. Here, we have tested our hypothesis that the super-nodulating En-b0-1 genotype is more salinity tolerant than a normal-nodulating genotype. The super-nodulating genotype and its parental normal-nodulating cultivar Enrei were grown in pots and subjected to saline conditions during the pre-flowering and reproductive growth stages. Under saline conditions imposed during pre-flowering, En-b0-1 formed heavier nodules, resulting in greater N uptake, higher photosynthetic activity, and greater biomass production compared with Enrei. Saline treatment increased the concentrations of sodium (Na) and chlorine (Cl) in all plant parts regardless of genotype; but in En-b0-1, the concentrations of these elements in shoots were significantly lower, while those in roots and nodules were higher than in Enrei. When the salinity treatment was imposed during the reproductive growth stages, En-b0-1 maintained higher N uptake, leading to better alleviation of salinity-induced yield reduction than in Enrei. The super-nodulating genotype En-b0-1 was more tolerant to salinity than its parental normal-nodulating cultivar, due to its superior nodulation and prevention of excessive accumulation of Na and Cl in shoots, which were retained in roots and nodules, thus supporting our hypothesis.
Quantitative trait loci (QTL) affecting the germination rate, coleoptile length, and shoot dry weight were analyzed under submerged and low temperature conditions using inbred lines derived from crossing the rice cultivars Ouu 365 and Arroz da Terra. The QTLs that increased the germination rate and shoot dry weight by Arroz da Terra allele were detected on the same region of chromosome 3, where the low temperature germinability gene, qLTG3-1, localized, suggesting that greater germinability might lead to increased shoot growth in paddy fields. The QTLs that increased the coleoptile length by Ouu 365 and Arroz da Terra alleles were detected on chromosome 8 and 11, respectively. The analysis of the known germinability genes suggested that functional allele of qLTG3-1 increased germination rates of the inbred lines. However, Rc which induced red pigmentation in pericarp declined the germination rates of the lines with functional qLTG3-1.
We identified chromosome regions affecting traits (CRATs) for 30 productivity-related traits using 2 sets of chromosome segment substitution lines (CSSLs). One was established using Nipponbare as the donor and Koshihikari as the background variety (Kos-Nip); and the other using Koshihikari as the donor and Nipponbare as the background (Nip-Kos). We identified 249 and 181 CRATs for 30 traits in Kos-Nip and Nip-Kos CSSLs, respectively. Donor alleles in 75 (Nipponbare) and 82 (Koshihikari) CRATs had positive effects on productivity. Among them, some CRATs represented superior effects as compared with the alleles in indica varieties Kasalath and Nona Bokra. On chromosome 1, a CRAT for panicle number (PN1) increased yield by about 1.4 times compared with Koshihikari. PN1 increased leaf area, while maintaining the SPAD value, which is an indicator of photosynthetic ability. Therefore, PN1 might have a pleiotropic effect on sink size and source ability, and thus could consequently improve yield. In only 29 CRATs for 13 traits (12% of total), corresponding CRATs with contrasting effects were detected in the 2 sets of CSSLs. These results suggested that the effect of a gene, might be affected by the genetic background. By using a database of single-nucleotide polymorphisms in Koshihikari and Nipponbare, we could narrow the candidate genes for 28/29 CRATs; to minimum 6 genes for CRAT related to plant height at the early stage and diameter at stem. Thus japonica rice could be a useful genetic donor for improving the productivity of another japonica variety.
The applicability of five nitrogen (N) dressing methods to rice cultivation was examined using the canopy spectrum-based nitrogen optimization algorithm (CSNOA), leaf area index (LAI), site-specific N management (SSNM), N nutrition index (NNI), and N fertilizer optimization algorithm (NFOA). After base-tiller N dressing (basal dressing and top dressing at the tillering stage) at low and normal levels, rice plants were grown by the above five N dressing methods. The effects of different N dressing methods on plant dry weight, plant N accumulation, grain yield, N use efficiency, and economic benefit were analyzed. Compared with the standard method, under the low base-tiller N dressing level, the optimum N dressing rate was decreased, and the economic benefit was increased by adapting the N dressing methods of CSNOA and SSNM, whereas the optimum N dressing rate was increased, and the economic benefit was decreased by the other three N dressing methods. Under the general base-tiller N dressing level, the optimum N rate, N-use efficiency and economic benefit were increased by all N dressing methods except the NFOA. These results indicated that the CSNOA and SSNM were two good techniques for quantifying N dressing in rice, with higher economic benefit, less N input, and better applicability under different base-tiller N dressing levels.
Plant-based diagnosis is one of the most important methods to determine nitrogen (N) content of crops. Our objective was to establish the relationship between soil-plant analysis development (SPAD) values and N nutrition index (NNI) during the three developmental stages of rice and apply the SPAD meter as diagnostic tools for predicting grain yield response to N fertilization. We determined the SPAD values of four uppermost fully expanded leaves of two rice cultivars at six N fertilization levels at three growth stages and examined the relationship between SPAD values and NNI. The critical N concentration (Nc) was 5.31 W-0.5 in Xiushui63, and 5.38 W-0.49 in Hang43, where W is the total shoot biomass. The correlation between SPAD value and NNI varied with the leaf position, developmental stage, and variety. The lower leaf appeared to be more sensitive to the N level than the upper leaf in the response of biomass, and could be more suitable as a test sample for N status diagnosis, especially in the booting and heading stage. The dependence of grain yield on SPAD values of the fourth fully expanded leaf (L4) was significant at booting stage (R2L4 = 0.82** in 2011, R2L4 = 0.72** in 2012). Ratio of SPAD values of L4 to that in the N-saturated plot (RSPAD) (R2L4 = 0.92** in 2011, R2L4 = 0.77** in 2012) and NNI (R2 = 0.96** in 2011, R2 = 0.86** in 2012) at booting stage demonstrated a closer relationship with grain yield.
The use of coffee grounds in crop fields were evaluated in terms of crop growth enhancement, soil improvement, and weed control during four successive cropping seasons for two years. Six summer and three winter green manure crops were grown from June 2009 to May 2011. In the first cropping season, the growth of all green manure crops was significantly inhibited by the application of 10 kg m-2 of coffee grounds. However, the inhibitory effects spontaneously diminished after the second cropping season (about 12 months later), and the growth of guinea grass, sorghum and sunflower was about 2-fold higher than that of the control. The application of horse manure at 10 kg m-2 effectively alleviated the inhibitory effects, even though the high concentration of coffee grounds was included. Although top dressing application of coffee grounds at 16 kg m-2 permitted weed control, the impact maintained enough only for half a year. Coffee grounds application effectively increased both carbon and nitrogen contents of soil and reduced CN ratio. The soil amendment effects were significantly higher in terms of nitrogen enrichment and CN ratio improvement as compared with the horse manure application. These results indicated that coffee grounds are useful to enhance long term crop growth, short duration weed control, and soil improvement in agricultural fields by considering the inhibitory effects on the plant growth for half year after the application. Agricultural use of coffee grounds was also discussed in term of fallow periods in crop rotation.
A large amount of nitrogen is redistributed from vegetative organs to the seeds during seed filling in soybean (Glycine max [L.] Merrill). However, the effect of nitrogen redistributed from leaves on the seed yield production is not clear. We evaluated the varietal difference in nitrogen redistribution and its contribution to the seed yield. Ten soybean cultivars were cultivated under conventional conditions in the field in Saga, Japan. The plant samples were collected at various reproductive stages, and then the nitrogen contents in each part were determined. The redistributed nitrogen was estimated by the difference in the nitrogen contents of leaves between the plants at the R5 and R7 stages. The nitrogen content of leaves began decreasing after R5 stage in all cultivars, indicating the start of nitrogen redistribution. About 13.8% to 37.9% of the total nitrogen in the seeds was estimated to have been redistributed from the leaf tissues in the ten cultivars. The seed yield was correlated positively with the amount of redistributed nitrogen from leaves but neither with the nitrogen concentration in the leaves at R5 nor with the proportion of redistributed nitrogen in the seeds. However, in high seed yielding years, 2008 and 2009, the seed yield was not associated with nitrogen redistribution; and the lowest nitrogen redistribution was associated with a relatively high seed yield in Tamahomare. Our results indicated that redistribution of a large amount of nitrogen does not always contribute to high seed yielding, implying the direct nitrogen uptake during seed filling could be more important factor for high seed yielding depending on the cultivars.