Increased grain yield and biomass allocation in rice under cool night temperature

Abstract

The effects of different night temperatures on grain yield were examined in rice (Oryza sativa L. Akita-63) during the ripening period. Plants were grown under two different night temperatures (22 and 27°C) from anthesis to harvesting. The day temperature was maintained at 27°C in both treatments. Although the final biomass at harvest did not differ between the treatments, the dry weight of the panicles was significantly greater in the cool night temperature treatment. This increase in panicle weight was associated with increases in the 1000-kernel weight and the ratio of filled spikelets. Although panicle respiration in the high night temperature treatment decreased to almost zero just after the cessation of grain filling, the net CO₂ fixation rate per day in the whole plant in this treatment tended to be higher, and this was associated with a higher level of starch accumulation. After grain filling, the starch content decreased and the final dry weight of other plant parts, including dead organs and new tillers, was greater in the high night temperature treatment. Thus, the noted decline in yield at the high night temperature led to changes in carbon allocation to new sinks for vegetative reproduction at the whole plant level. From these results, we considered the possibility that a cool night temperature tends to favor carbon allocation to panicles, resulting in higher yield.     

Effects of foliar spraying with new zinc sources on rice seed enrichment,nutrition, and productivity

New Zn sources have emerged recently, which may boost the beneficial effects of leaf sprays on rice cropping. Thus, this study aimed to compare the effects of foliar sprays using Zn chelate against those with new Zn sources such as sorbitol-stabilised Zn nitrate and Zn oxide nanoparticles on rice seed enrichment and production. Treatments were arranged in a completely randomised design, comprising of three Zn sources and four Zn concentrations with four replicates. Rice plants were sprayed three times: at the beginning of tillering, maximum tillering, and booting stage. Experimental unity consisted of 7-dm³ pots filled with 5-dm³ medium textured sand. Each pot had 10 plants, of which 6 randomly harvested at the flowering stage and the remaining at the maturity stage. Plant dry matter, content and accumulation of Zn in the shoot, seed Zn content, and seed production at the grain-filling stage were also estimated. Seed production and Zn accumulation showed a quadratic behaviour with the use of novel sources. Overall the new Zn sources were more effective than the traditional EDTA chelated Zn in terms of rice seed production and quality, especially the sorbitol-stabilised Zn nitrate.     

Varietal differences in tillering ability of fourteen japonica and indica rice varieties

Field experiments were conducted to clarify the relation between the tillering ability and morphological characters, dry matter production, or nitrogen absorption among 14 rice varieties including different ecospecies with different plant types, and about the same heading time. Tiller number varied widely among the varieties and the number of tillers per plant at the maximum tiller number stage ranged between 14.3 and 39.5 in 1995 and 12.2 and 34.6 in 1996. Among all the varieties, IR 36 followed by Suweon 258 produced the highest maximum tiller number and Dawn produced the lowest maximum tiller number. The plant length and the specific leaf area, i.e. one of the indicators of leaf thickness, showed a strong negative and positive significant correlation, respectively, with the maximum tiller number. The varieties with a shorter plant length produced shorter and thinner leaves which would provide less competition for dry matter and nitrogen between mother stem and tillers and among tillers. This resulted in a higher efficiency of tiller production in the higher-tillering varieties for the same amount of dry matter production and nitrogen absorption. Percentage of productive tillers widely varied among the varieties, ranging from 42 to 73% in 1995 and from 50 to 81% in 1996. Semidwarf indica and japonica-indica varieties showed a lower percentage of productive tillers than the Japanese and tall indica varieties, and high-tillering varieties IR 36 and Suweon 258 produced the highest number of dead tillers, which resulted in the lowest percentage of productive tillers. The number of dead tillers depended mainly on the extent of competition for carbohydrates produced and nitrogen absorbed from the maximum tiller number stage to heading among tillers, although the increasing ratio of dead tillers was higher in indica varieties than in japonica varieties with a decrease in the amounts of these substances.     

Impact of plant genotype and nitrogen level on rice growth response to inoculation with Azospirillum sp. strain B510 under paddy field conditions

Abstract

Twenty rice cultivars, including three genetically-distinct groups (japonica, indica-1, and indica-2), were evaluated for their response to inoculation with Azospirillum sp. strain B510 in paddy fields with standard nitrogen (SN) and low nitrogen (LN) fertilization. In the SN field, the tiller numbers in most indica-2 cultivars, 37?days after transplanting (DAT), were significantly increased by the B510 inoculation, whereas those in 4 japonica cultivars were significantly decreased. A similar growth response was observed in the LN field, although the impacts of the B510 inoculation were more varied than in the SN field. At 58 DAT, the tiller numbers in most cultivars were lower or unaffected by the B510 inoculation under both SN and LN conditions, except that the tiller number of the Nipponbare cultivar, which is classified as japonica, was significantly higher in the LN field only. These results suggest that the effects of inoculation with Azospirillum sp. strain B510 on the growth of rice plants, especially on tiller numbers at the early growth stage, vary depending on the rice genotype, as well as nitrogen level. Therefore, the plant genotypes, growth stages, and fertilization managements must be considered when a plant-associated bacterium is evaluated for beneficial effects under field conditions.     

Excessive application of farmyard manure reduces rice yield and enhances environmental pollution risk in paddy fields

The present study examined the effect of excessive application of farmyard manure (FM) on rice production and environmental pollution in paddy fields of Japan. A long-term field experiment was conducted during the period 1976–2006 to examine the trends of rice yield and yield components as affected by the excessive FM application (20 Mg ha^?1 year^?1 containing 110 kg N, 180 kg P₂O₅, and 320 kg K₂O). Rice growth, soil fertility, and surface water quality were also assessed in the final year (2006). The results obtained were compared with those of a conventional practice with recommended doses of inorganic fertilizer (IF), i.e. 85 kg N, 68 kg P₂O₅, and 53 kg K₂O ha^?1 year^?1, and an unfertilized control (CR). The excessive FM application resulted in a gradual decrease in grain yield, which was mostly explained by the reduction of grain fertility under the luxuriant rice growth. This reduction may have been due to the higher accumulation of soil nutrients such as N, P, and K. Moreover, the excessive FM application increased chemical oxygen demand, total P, and soluble K concentrations in the paddy surface water and their effluent loads compared to the conventional practice with the recommended IF application.     

水稻雄蕊导管发育研究

本文以水稻粤泰保持系为材料，采用ATPase定位方法研究了单核至三核花粉期雄蕊导管的发育。单核边位花粉期，分化的导管胞质变浓厚、细胞核染色质浓缩、核转变为新月形并出现凋亡小体；此外，导管内物质也可以大分子形式直接撤离。单核边位晚期，雄蕊导管发育成熟。在二核和三核花粉期，导管内重新出现具有ATPase活性的物质，同样的现象也存在于农垦58s可育花药成熟导管中。以上结果暗示水稻雄蕊导管分化存在程序性死亡及非程序性死亡多种途径，水稻成熟导管内具有ATPase活性物质可能是一种普遍现象。     

Arsenic accumulation by rice grown in soil treated with roxarsone

Poultry litter is widely used as a fertilizer for lowland rice in Taiwan and China. However, the organic‐arsenic compound roxarsone (additive of poultry feed) in poultry litter can be absorbed by the plants and the resulting arsenic (As) contamination may pose a serious threat to human health. This study used various amounts of poultry litter contaminated with roxarsone in pot experiments to evaluate the effect of roxarsone on rice agronomic parameters and the bioaccumulation of total and inorganic As in rice‐plant tissues. Rice‐grain yield decreased significantly with increasing As content of the soil, and the critical threshold that killed rice was 200 mg roxarsone (kg soil)^–1. The As concentrations in root, straw, leaf, husk, and grain increased with increasing soil As (p < 1%). At 100 mg roxarsone per kg of soil, the As concentration in the rice grain exceeded the statutory permissible limit of 1.0 mg As (kg dry weight)^–1 and at 25 mg roxarsone (kg soil)^–1, the inorganic As concentrations in grains exceeded the statutory limit of 0.15 mg of inorganic As kg^–1 in China. For all treatments, the As concentrations in various plant tissues at maturity follow the order: root > stem > leaf > husk > grain. Arsenite was the predominant species in root, straw, and grain, while arsenate was the predominant species in leaf and husk. No significant difference existed between the amounts of arsenite and arsenate when various amounts of poultry litter were applied. This result illustrates that large amounts of added roxarsone are not only toxic to rice but also accumulate in grains in the inorganic As forms, potentially posing a threat to human health via the food chain.     

Zinc alleviates growth inhibition and oxidative stress caused by cadmium in rice

A hydroponic experiment with two rice cultivars differing in cadmium (Cd) tolerance was conducted to investigate the alleviating effect of zinc (Zn) on growth inhibition and oxidative stress caused by Cd. Treatments consisted of all combinations of two Zn concentrations (0.2 and 1 μM), three Cd concentrations (0, 1, and 5 μM), and two rice cultivars (Bing 97252, Cd‐tolerant; Xiushui 63, Cd‐sensitive). Cd toxicity caused a dramatic reduction in plant height and biomass, chlorophyll concentration and photosynthetic rate, and an increase in Cd concentration in both roots and shoots, malondialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in shoots. The response of all these parameters was much larger for Xiushui 63 than for Bing 97252. Addition of Zn to the medium solution alleviated Cd toxicity, which was reflected in a significant increase in plant height, biomass, chlorophyll concentration, and photosynthetic rate, and a marked decrease in MDA concentration and activity of anti‐oxidative enzymes. However, it was noted that Zn increased shoot Cd concentration at higher Cd supply, probably due to the enhancement of Cd translocation from roots to shoots. Therefore, further studies are necessary to determine the effect of Zn supply on Cd translocation from vegetative organs to grains or grain Cd accumulation before Zn fertilizer is applied to Cd‐contaminated soils to alleviate Cd toxicity in rice.     

根癌农杆菌介导水稻基因转化研究进展

简要综述了根癌农杆菌介导水稻基因转化的优点及转化后代的遗传学行为 ,着重分析了影响农杆菌介导水稻基因转化的各种因素和存在问题     

Potassium requirement in relation to grain yield and genotypic improvement of irrigated lowland rice in China

The yield of rice (Oryza sativa L.) has increased substantially with the development of new cultivars, but the role of potassium (K) requirement for the increase in grain yield and the genotypic advance is still unclear. In order to investigate this relationship a database of 1199 on‐farm measurements (harvest index 0.4) comprising > 400 modern rice cultivars was collected during 2005–2010 across major irrigated lowland rice–production regions of China. This was used to evaluate the relationships among K requirement, grain yield, and genetic improvement. Across all the sites and seasons, mean reciprocal internal efficiency of K (RIE‐K, kg K [t grain produced]^–1) was 19.8 kg K (t grain)^–1 and rice yield averaged 8.7 t ha^–1. Considering four levels of grain yield (< 7.5, 7.5–9, 9–10.5, and > 10.5 t ha^–1), the respective RIEs were 18.7, 19.4, 20.5, and 21.7 kg K (t grain)^–1. The gradual increase in the RIE‐K with yield was attributed mainly to the increase in straw and grain K concentration and the decrease in the K harvest index. The RIE‐K values for ordinary inbred, ordinary hybrid, and “super rice” were 18.5, 20.1, and 19.9 kg K (t grain)^–1, respectively. Examining the historical development of rice cultivars, the RIE‐K decreased from 40.9 (Nanjing1, early tall, inbred) in the 1950s to 19.8 (IR24, semi‐dwarf, ordinary inbred) in the 1970s, and then increased to 20.9 (Shanyou63, modern ordinary hybrid) in the 1980s and 20.6 kg K (t grain)^–1 (II‐you084, “super” rice) in the 2000s. This variation in RIE‐K among grain‐yield levels and cultivars highlights the importance of information on rice K requirement in calculating K balance and optimal K‐fertilizer rate for rice production.     

Positional difference in potassium concentration as diagnostic index relating to plant K status and yield level in rice (Oryza sativa L.)

Plant tissue testing is used as a guide for rice (Oryza sativa L.) fertilization and has been extensively used in the diagnosis of potassium (K) deficiency. However, little attention has been paid to the variation in the diagnostic index of K status in different parts of the rice plant. Here, we assessed the feasibility by testing K concentrations of whole plants, leaf blades and leaf sheaths to develop a suitable diagnostic index of plant K status and yield level in rice under different K application rates. The results showed that this research could satisfy the requirements of K status diagnosis, based on the quadratic-plus-plateau relationship between K application rates and grain yield. The K concentrations of the leaf blades and leaf sheaths on the main stem showed differences based on position. Leaf blade K concentrations significantly decreased from the top of the plant to the bottom in the effective tillering and jointing stages. Conversely, K concentrations in the lower leaf blades exceeded those in the upper leaf blades in the booting and full heading stages. K concentrations in the leaf sheath were significantly reduced with declining leaf position except during the jointing stage under high K treatments. Leaf sheath/leaf blade K concentration ratios increased significantly more in lower tissues than in upper plant tissues. Correlation analysis showed that the K concentrations of all sampled plant tissues were positively correlated to plant K uptake and grain yield. However, K concentrations of the whole plant were more useful as a diagnostic index at the effective tillering stage than at other growth stages. Leaf sheaths in lower positions were preferable to upper leaf sheaths and all leaf blades for evaluating plant K status, although their K concentrations were greatly influenced by plant growth stage. Furthermore, this study demonstrated that the ratio between the K concentrations of the first and fourth leaf blades (LBKR_1/4) was grouped into significantly exponential curves (P < 0.01) to describe the relationship between plant K uptake and relative grain yield. Thus, LBKR_1/4 could be an ideal indicator of rice plant K status and yield level, as it eliminated the effects of plant growth stage.     

水稻蜡质合成相关基因OsGL1-5的表达模式及逆境响应特征分析

通过生物信息学方法对水稻蜡质合成相关基因OsGLl-5启动子序列特点进行分析;并以水稻中花11不同组织和发育时期的穗子为材料,通过半定量RT-PCR及mRNA原位杂交技术分析OsGLl-5的时空表达特征;同时,分别以200mmol·L-1 NaCl、100μmol· L-1 ABA和1.0％ H2O2处理水稻幼苗,通过半定量RT-PCR分析逆境胁迫下OsGL1-5的表达模式.生物信息学分析表明,OsGL1-5启动子中包括大量与干旱、冷、盐等多种逆境胁迫相关的调控序列.时空表达特征分析表明,OsGL1-5主要在不同发育时期的穗子中表达,且表达部位集中在稃片的毛状体和花药绒毡层中,叶中表达量相对较低,而茎和根中没有检测到表达.NaCl、ABA以及H2O2等逆境胁迫下,OsGL1-5表达量在不同处理时间有所增加.     

缺钾对水稻不同品种光合和能量耗散的影响

试验测定了钾敏感型(二九丰)和钾钝感型(原丰早)两个水稻品种在缺钾处理41.d后其剑叶的生长、光合光响应曲线、叶绿素荧光参数光响应曲线和暗弛豫动力学曲线。结果表明,缺钾降低了水稻剑叶的光合作用,显著抑制了生长。但是缺钾条件下导致两个水稻品种净光合速率(Pn)下降的主导因子并不相同。在缺钾条件下,原丰早(YFZ)剑叶的Pn随气孔导度(Gs)和胞间CO2浓度(Ci)的下降而下降,但叶绿素荧光参数和叶绿素含量几乎没有变化,说明其Pn下降主要归于气孔的限制。缺钾处理41.d后,二九丰(EJF)在低光强下[500mol/(m2.s)],Pn随Gs和Ci下降,但在更强的光强下,Pn和Gs继续下降,而Ci开始上升,并在1200mol/(m2.s)处超越了对照,说明此时主导因子不单受气孔限制,还受非气孔因子限制;它的光饱和点从1200mol/(m2.s)下降到大约500mol/(m2.s);同时,其荧光参数Fv/Fm、ФPSII、qP和ETR随光强上升而迅速下降,而L(PFD)、E和PP迅速增加,NPQ在1200mol/(m2.s)光强下上升,但是在高光强下却迅速降低,甚至低于对照,而且Fm、Fv/Fm下降,Fo上升,均说明缺钾处理可能使光合机构受到了伤害,发生了光抑制。对非光化学猝灭的分析得到其中间组分qNm可能起了更大的能量耗散作用,部分激发能从PSⅡ转移到PSⅠ,降低了PSⅡ耗散能量的压力。以上结果表明,两品种对钾敏感性不同极可能也与缺钾条件下光保护能力的差异有关。     

高钾供应加剧了水稻叶片缺镁诱导的氧化胁迫

Magnesium （Mg） deficiency in plant affects photosynthesis and many other metabolic processes. Rice （Oryza sativa L. cv. ＇Wuyunjing 7＇） plants were grown in hydroponics culture at three Mg and two potassium （K） levels under greenhouse conditions to examine the induction of oxidative stress and consequent antioxidant responses in rice leaves due to Mg deficiency. At low Mg （0.2 mmol L 1 Mg supply for two weeks after transplanting） and high K （6 mmol L^-1） for 21 days, the rice plants showed severe Mg deficiency and a significant decreases in the dry matter production. The Mg deficiency in leaves decreased chlorophyll concentrations, photosynthetic activity, and soluble protein, but significantly increased the concentrations of soluble sugars and malondialdchyde （MDA） and the activities of superoxide dismutase （SOLD, EC 1.15.1.1）, catalase （CAT, EC 1.11.1.6） and peroxidase （POD, EC 1.11.1.7）. In addition, Mg concentrations in the leaves and in the shoot biomass were negatively related to the activities of the three antioxidative enzymes and the concentration of MDA in leaves. There were very significant interactive effects between Mg and K supplied in the culture solution on shoot biomass yield, chlorophyll content, photosynthesis rate, the activities of SOD, CAT and POD, and MDA content in the leaves of rice. It is suggested that the high K level in the nutrient solution aggravated the effect of low Mg supply-induced Mg deficiency and created the oxidative damage in rice plants.     

Cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.) treated with a nutrient solution containing cadmium

To obtain direct evidence for the translocation of cadmium (Cd) via the phloem, we measured the Cd concentrations in the phloem sap of 5-week-old rice plants (Oryza sativa L. cv. Kantou) treated with a nutrient solution containing Cd. The phloem sap was collected from the leaf sheaths through the cut ends of stylets of the brown planthopper (Nilaparvata lugens Stål.). Cd concentrations in the phloem sap from the plants treated with 10 and 100 µM Cd for 3 d were 4.6 ± 3.4 and 17.7 ± 9.8 µM, respectively. Detection of Cd in the phloem sap indicated that Cd was translocated via sieve tubes in rice plants. Cd concentrations in the xylem exudate collected from the cut basis of the leaf sheaths of the plants treated with 10 and 100 µM Cd for 3 d were 18.9 ± 6.4 and 64.2 ± 14.6 µM, respectively. Cd concentrations in the phloem sap were significantly lower than those in the xylem exudate, indicating that Cd is not concentrated during the transfer from xylem to phloem. To our knowledge, this is the first determination of Cd concentrations in the phloem sap of plants, and the first direct proof that Cd is translocated via sieve tubes in rice plants.     

Tolerance of rice cultivars to iron toxicity

Iron toxicity is an important growth‐limiting factor for flooded rice production in various parts of the world, including Brazil. Data related to the reaction of rice cultivars to iron concentrations are limited, especially for large numbers of cultivars. Forty rice cultivars were grown in a greenhouse in nutrient solutions containing 0.09, 0.89, and 1.78 mM Fe (5, 50 and 100 ppm Fe). The effects of excess iron were measured on plant height, root length, and root and shoot dry weight. Root and shoot dry weight were found to be more sensitive to excess iron concentration. Based on dry matter yield, reduction of shoots at higher Fe concentrations compared to the optimum or control treatment, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible.

The effect of Fe concentrations on concentrations and contents of other nutrient was also investigated. Higher concentration of Fe in the nutrient solution exerted an inhibiting effect on the concentrations and contents of almost all macro and micronutrients.     

铵态氮/硝态氮对水稻铝吸收的影响及其机制研究

选用两个水稻品种武运粳7号（耐铝品种）和扬稻6号（铝敏感品种）作为实验材料,利用水培试验,通过长期和短期处理相结合的方式研究了NH4+-N和NO3--N对水稻Al吸收的影响及其作用机制。结果表明,与NH4+-N相比,NO3--N促进了水稻对Al的吸收。而且随着NO3--N浓度的提高,水稻根中Al含量显著增加,随着NH4+-N浓度的提高,水稻根中Al含量显著降低。这些结果表明NH4+-N和NO3--N对水稻Al吸收的影响具有浓度效应。当向Al溶液添加pH缓冲剂后,NH4+-N和NO3--N对根尖Al累积的影响变小,表明NH4+-N和NO3--N处理下溶液pH的变化可能是NH4+-N和NO3--N对水稻Al吸收影响不同的一个原因。     

Using farmer knowledge to combat low productive spots in rice fields of a Sahelian irrigation scheme

In the oldest sections of Burkina Faso's largest irrigation scheme in the Sourou Valley (13° 10′ N, 03° 30′W) rice (Oryza sativa L.) yields dropped from about 5 to 6 t ha⁻¹ in the early 1990s, shortly after establishment of the scheme, to 2 to 4 t ha⁻¹ from 1995 onwards. Farmers blamed this yield decline on the appearance of 2 to 20 m diameter low productive spots. According to farmers and field measurements, the low productive spots decreased yields by 25–50 per cent. The low productive spots are caused by Zn deficiency. Low Zn availability is related to the very low DTPA‐extractable Zn content of the soil (0·08–0·46 mg kg⁻¹), the alkaline‐calcareous character of the soil, the non‐application of Zn fertilizers, and a relatively large P fertilizer dose (21 kg P ha⁻¹). Farmers were correct in relating the calcareous nature of the soil to the presence of the low productive spots. They were instrumental in identifying application of decomposed organic resources (e.g. rice straw at 5 t ha⁻¹) as a short‐term solution that increases yields by 1·5 to 2·0 t ha⁻¹. Application of Zn fertilizer (10 kg Zn ha⁻¹) in 29 farmer fields in the 2001 dry season eradicated the low productive spots and increased yields from 3·4 to 6·0 t ha⁻¹. Although application of Zn fertilizer is strongly recommended, it is not yet available in Burkina Faso. Based on a comparison of fertilizer prices on the world market and the local market, we expect that the use of Zn fertilizers will be highly profitable (cost/value ratio ≫ 2). Despite the relatively recent introduction of irrigated rice cropping, most farmers showed a good understanding of cropping constraints and possible solutions. Both farmers and researchers mutually benefited from each other's knowledge and observations. Copyright © 2004 John Wiley & Sons, Ltd.