Enclosed stigma contributes to higher spikelet fertility for rice(Oryza sativa L.) subjected to heat stress

With global warming, rice plants may be subjected to heat stress more regularly during the heatsensitive flowering stage, causing spikelet sterility and grain yield loss.Stigma exsertion is considered to increase pollen reception and promote female reproductive success.The aim of this study was to investigate the role of stigma exsertion on spikelet fertility at high temperatures.Five rice cultivars(Liangyoupeijiu, Shanyou 63, Huanghuazhan, Nagina 22, and IR64) with differing degrees of stigma exsertion were cultivated and exposed to high temperature at anthesis.Heat-tolerant cultivars did not always show a high percentage of spikelets with exserted stigmas, and vice versa.Irrespective of the presence of more pollen grains on exserted stigmas, spikelets with exserted stigmas did not show greater spikelet fertility than spikelets with fewer exserted stigmas or hidden stigmas under heat stress.GA3 application augmented the percentage of spikelets with exserted stigmas;however, it did not increase spikelet fertility under heat stress.Spikelet fertility of whole panicles was negatively correlated with the percentage of spikelets with exserted stigmas, but positively with that with hidden stigmas.Viability of the hidden stigmas was less reduced than that of exserted stigmas under heat stress, suggesting that hidden stigmas have an advantage in maintaining viability.Heat stress delayed anther dehiscence and reduced the viabilities of both exserted stigmas and pollens, thereby causing low spikelet fertility.Together, these results suggest that high spikelet fertility does not depend on stigma exsertion and that enclosed stigma generally contributes to higher spikelet fertility and heat tolerance under high-temperature conditions during flowering in rice.     

Response of Spikelet Number per Panicle in Rice Cultivars to Three Transplanting Densities

Abstract

Spikelet number per panicle (SPP), differentiated spikelet number per panicle (D-SPP), and preflowering aborted spikelet number per panicle (A-SPP) were examined in five rice cultivars at three planting densities (HD; high, MD; medium, LD; low planting density) in the field condition. Rice plants at LD produced a higher panicle number per plant but lower panicle number per unit area, accompanied by higher D-SPP and SPP, on average. A-SPP and the ratio of A-SPP to D-SPP (%A) showedno consistent trends. There was a broader range of D-SPP values at LD than at HD because of larger D-SPP in higher order panicles (panicles with a higher spikelet number). D-SPP was smaller in lower order panicles in all cultivars and years, whereas %A increased. D-SPP and SPP of each panicle were positively correlated with tiller size (tiller height, leaf area, and neck internode diameter). Spikelet production efficiency for D-SPP or for SPP (spikelet number per leaf area) of each tiller was higher in IR65564-44-51 (NPT65) and Akihikari than in the other cultivars, indicating a greater capacity of tillers to produce spikelets or support spikelet growth. In each cultivar except NPT65, spikelet production efficiency for D-SPP increased as panicle order decreased, whereas spikelet production efficiency for SPP remained constant or decreased. This finding indicates that irrespective of planting density, lower order panicles produce more spikelets than they can afford physiologically, but they were regulated downward to a nearly constant value in four cultivars. In NPT65 different from other cultivars, spikelet production efficiency for D-SPP was lower in lower order panicles.     

不同时期弱光胁迫对晚稻不同耐弱光品种源库特征及叶片保护酶活性的影响

目的 本研究旨在明确弱光胁迫下不同弱光耐性品种在源库特征及叶片保护酶活性变化方面的差异,揭示其耐弱光胁迫的机制,为双季稻高产稳产新品种的选育及抗逆栽培提供理论指导。方法 以2个对弱光胁迫耐性存在显著差异的晚稻品种为材料,通过设置不同时期的遮光处理,研究弱光胁迫时期对晚稻不同耐性品种的源库特征及叶片保护酶活性的影响。结果 结果表明,不同时期弱光胁迫对晚稻生长有重要影响,分蘖期弱光胁迫下晚稻分蘖数、每穗粒数及总颖花量减少,叶面积下降,产量降低;幼穗分化期弱光胁迫下晚稻分蘖数和每穗粒数减少,总颖花量、叶面积、结实率均下降,产量降低;灌浆期弱光胁迫下水稻叶片净同化率降低,结实率和千粒重下降,产量降低。不同时期弱光胁迫对晚稻产量的影响表现为灌浆期>幼穗分化期>分蘖期。结论 耐弱光胁迫型品种能通过增加叶片的长宽度减少叶面积的下降,叶片含氮量保持相对稳定,叶片中SOD、CAT等保护酶活性保持在较高水平,POD活性保持相对稳定,叶片净同化率下降幅度小,在弱光胁迫下实现“强源”,减产率相对较低。弱光胁迫下具有较强的叶面积补偿能力和适宜氮含量以及较高的保护酶活性是水稻耐弱光胁迫的重要机制。     

Cropping calendar options for rice-wheat production systems at high-altitudes

The onset of rains during dry to wet transition fallow periods in rice-wheat production systems in Nepal cause substantial losses of soil nitrogen if the system is improperly managed. To make use of available nutrients and water, this transition period can either be shortened by early rice planting, or be extended by late planting, allowing a third crop to be grown. Shifting planting dates would require rice genotypes adapted to the different environments. Crop duration is influenced by both vegetative and reproductive development, which in turn is influenced by the photo-thermal environment and genotypic responses to it. An experiment was conducted to derive genotypic photo-thermal constants from phenological observations on diverse rice cultivars, which were then applied to the concept of the phenological model RIDEV to design cropping calendar options. Environmental effects on variation of crop duration were determined by planting at different dates. The risk of yield losses to sterility caused by low temperatures was estimated by simulation. Thirty-one different genotypes of rice were planted at 8 dates in 15-day intervals starting 27 April 2004 at the experimental field of the Regional Agriculture Research Station, Lumle, Nepal. The shortest duration to flowering was observed for planting dates in late May and early June. Simulation of flowering dates with RIDEV yielded correct results only for the early planting dates. For later planting dates simulated flowering dates showed an increasing deviation from the observed. In most cultivars, minimum air temperature below 18 °C during booting to heading stages caused near-total spikelet sterility and a specific delay in flowering. However, the chilling tolerant cultivars Chomrong and Machhapuchre-3 cultivated at high altitude showed less than 30% spikelet sterility even at 15 °C. Simulating crop durations with the derived thermal constants allowed evaluating the different calendar options for high altitude systems.     

Low temperature-induced sterility in rice: Evidence for the effects of temperature before panicle initiation

Spikelet sterility of rice (Oryza sativa L.) results from low temperatures during panicle development. However, this temperature alone cannot fully explain the fluctuations in sterility observed in the field, since the susceptibility of rice plants to low temperature often changes according to its physiological status during sensitive stages. In the present study, we examined whether temperatures before the panicle initiation stage (PI) influence the plant's susceptibility to sterility during panicle development. To test this, we conducted a 2-year pot study and an analysis of field data using a model of cooling degree-days (CDD). In the pot study, the air temperature (T_a) and water temperature (T_w) were controlled independently for 3 weeks during the vegetative growth stage before PI. After PI, the plants were submerged in a cool water bath at a critical temperature of 19.5 °C to induce floral sterility. We found that low T_w during vegetative growth significantly increased the sterility. Low T_a during vegetative growth also significantly increased the sterility, but this effect was diminished by warm T_w even at low T_a. There was a close and negative correlation between sterility and T_w during vegetative growth. In the analysis of field data, we introduced CDD using temperatures below a threshold level of 20 °C to represent the magnitude of the exposure to low temperature from PI to the heading stage. Data of T_a was used for this analysis because data of T_w was scare. The CDD model was applied to 77 independent data sets collected at nine Agricultural Research Centers during four typical cool summers (1980, 1988, 1993, and 2003) in northern Japan. Year-to-year variations in sterility at one site were roughly accounted for by the variations in CDD, but large deviations were observed among the years. The deviations were related to T_a averaged over the 30-day period before PI. For a similar level of CDD, the lower the T_a before PI, the greater the sterility. Similar deviations were observed in the between-site relationships between sterility and CDD, and these deviations were related with the T_a before PI. These results suggest that temperatures before PI, and especially T_w, change the susceptibility of a rice plant to low temperatures during panicle development.     

Breeding efforts to mitigate damage by heat stress to spikelet sterility and grain quality

Global warming is predicted to aggravate the risk of unstable crop production. It is of great concern that damage to rice spikelet sterility and grain quality will increase, resulting in yield and economic losses. To secure the global food supply and farmers’ income, the development of rice cultivars with heat resilience is a pressing concern. Regarding spikelet sterility, rice cultivars with heat tolerance at different growth stages have been identified in recent years. The early-morning flowering (EMF) trait is effective in heat escape because it shifts the time of day of flowering to earlier in the morning when it is cooler. Although varietal differences are very small, there are some genetic resources for EMF in wild rice accessions. Regarding heat-induced grain chalkiness, heat-tolerant japonica cultivars for mitigating white-back type of chalky grains (WBCG) were found. Quantitative trait loci for heat tolerance at flowering, EMF, and for WBCG in grain quality have been mapped on the rice chromosomes. Further genetic efforts have been successfully connected to the development of near-isogenic lines for each trait with tagged molecular markers. These breeding materials are quite unique and useful in facilitating marker-assisted breeding toward the development of heat-resilient rice in terms of spikelet sterility and grain quality.     

水稻器官形态和干物质积累对穗分化不同时期高温的响应

为明确水稻穗分化期高温对生长发育所造成的影响,以耐热籼稻黄华占和热敏感籼稻丰两优6号为材料,利用人工气候箱在穗分化期进行40℃(10:00-15:00)高温处理,以人工气候箱32℃适温处理为参考,室外环境温度为对照(CK),研究枝梗-颖花分化期(Ⅰ期)和花粉母细胞形成-减数分裂期(Ⅱ期)高温胁迫对水稻器官形态及干物质积累的影响。结果表明:1)Ⅰ期高温抑制幼穗分化,使穗分化期延长2.5~8.8 d;Ⅱ期高温阻碍水稻抽穗,导致穗分化期延长6.8~7.1 d,显著缩短上部茎节,降低抽穗度,其中热敏感品种降幅大于耐热品种;2)穗分化期高温处理显著降低每穗颖花数和颖花大小,颖花数下降原因在不同处理时期间存在差异,Ⅰ期高温减少颖花分化数;而Ⅱ期高温显著加速颖花退化,两个品种退化幅度均达50%以上,并显著降低了花药大小和颖花受精率,热敏感品种丰两优6号受高温影响要大于耐热品种;3)高温对叶片生长有促进作用,Ⅱ期高温处理表现尤为明显,两个时期高温处理对上3叶净光合速率和水稻单茎干物质积累没有显著影响。Ⅰ期高温不同部位间干物质积累无显著差异,而Ⅱ期高温显著降低茎鞘和穗部干物质积累,但高温导致高节位分枝发生,积累了一部分干物质,整体上单茎干物质积累量并没有显著下降。     

Injuries to Reproductive Development Under Water Stress,and Their Consequences for Crop Productivity

Summary

Reproductive development of plants, from meiosis to seed set, is highly vulnerable to water deficit. Two peaks of high sensitivity are encountered during this period. The first one occurs during meiosis in reproductive cells, and is common to all species studied. Water deficit at this stage causes pollen sterility, but usually affects female fertility only when the stress is severe. Pollen sterility does not result from a desiccation of the reproductive organs, but is an indirect consequence of water deficit in the vegetative parts, and may be mediated by a transportable sporocidal signal. The second peak of sensitivity occurs during flowering, and is conspicuous in rice, maize and some dicots. Depending on species, stress during this period can cause loss of pollen fertility, spikelet death or abortion of newly formed seed. These injuries, unlike those caused by the meiotic-stage stress, are associated with a decline in the water status of the reproductive structures. Changes in carbohydrate availability and metabolism appear to be involved in the effects of stress at both these stages.     

Morpho-Physiological Response of Oryza glaberrima to Gradual Soil Drying

Soil drought occurrence during dry season has been the main constraint, besides prolonged flooding during rainy season, in increasing cropping intensity and rice productivity in tropical riparian wetland. Use of drought tolerant rice genotype might be a suitable option for overcoming such problem. This study focused on the effects of gradual soil drying during early vegetative growth stage on morphological and physiological traits of five Oryza glaberrima genotypes, namely RAM12, RAM14, RAM59, RAM97 and RAM101, and two Oryza sativa subsp japonica genotypes, i.e. Koshihikari and Minamihatamochi. The plants were subjected to 6 d of gradual soil drying condition from 15 days after transplanting (DAT) to 20 DAT, and were allowed to recover until 22 DAT. Gradual soil drying reduced plant growth as indicated by dry mass accumulation. Drought reduced stomatal conductance and increased leaf rolling score of all the genotypes. All the genotypes showed comparable response on stomatal conductance, but O. glaberrima genotypes performed higher in leaf rolling recovery. Meanwhile, O. sativa genotypes decreased total leaf area and specific leaf area, but increased specific leaf weight in order to avoid further damages due to drought stress. Drought tolerance mechanisms in RAM101, RAM12, RAM59 and RAM14 were associated with leaf morpho-physiological responses, root traits and dry biomass accumulation.     

盐胁迫下 4 个不同耐盐基因型水稻 Na+ 、K+ 积累效应

选取耐盐性较强的水稻株系‘Fl478’、‘JX99’、‘Pokkali’和盐敏感型品种‘IR29’,设置 6 个 NaCl 浓度梯度处理, 分别为 0、0.1%、0.2%、0.3%、0.4%、0.5%,采用桶栽土培的方法培育至孕穗期,研究盐胁迫对孕穗期水稻植株不同 器官 Na+ 、K+ 分配规律与积累的影响。结果表明：（1）盐胁迫下水稻株系不同器官 Na+ ,K+ 的积累效应存在差异,水稻 株系耐盐性的差异主要表现在根系,而叶鞘对 Na+ 、K+ 的吸收与分配的差异明显。（2）耐盐植株根系聚 Na+ 能力较强, 叶片、叶鞘积累较多的 K+ ,而感盐品种根系积累 K+ 和 Na+ 以缓解根系渗透胁迫,调节根系 Na+ /K+ 平衡稳态,保持水稻 正常的代谢活动。（3）叶鞘是水稻植株关键的 Na+ -K+ 调库,通过吸收和分配 Na+ 来调节根、叶、叶鞘 Na+ /K+ 平衡以提 高水稻耐盐性。（4）耐盐株系叶鞘向叶片选择运输 K+ 的能力、限 Na+ 运输能力强于盐敏感品种,叶鞘对 Na+ 、K+ 吸收 与分配运输能力的大小,决定水稻株系的耐盐性,具体表现耐盐品种叶鞘向吸收与运输 K+ 能力较强、根系限 Na+ 能力 显著高于感盐植株。（5）0.4%~0.5%盐浓度限制水稻叶鞘 Na+ -K+ 库吸收与分配能力,各组织中 Na+ /K+ 失衡,植株耐盐 性降低,受盐害程度加深。（6）盐胁迫促进水稻株系叶鞘向根系吸收较多 Na+ 和向叶片、根系输出 K+ ,却限制 Na+ 对 叶片的分配,保证根系保持较高的 K+ /Na+ ,耐盐幼嫩叶片积累较多的 K+ 以维持叶片组织保卫细胞渗透平衡,保证水稻 植株获得生活必需的光合原料,而盐敏感植株积累的 K+ 主要用于缓解组织渗透胁迫,以维持正常生命活动。     

Response of chickpea genotypes to low temperature stress during reproductive development

Low temperature at flowering is a major constraint to improved yield of chickpea in many regions of the world. In particular, cool dryland environments such as southern Australia, parts of the Indian sub-continent and the Mediterranean would benefit from cultivars with the ability to flower and set pods early in the growing season before soil moisture becomes a limiting factor. This paper demonstrates that low temperature (less than 15 °C) affects both the development and function of reproductive structures in the chickpea flower. Aspects of the male and the female gametophyte phases of development are described. Comparisons between chilling sensitive genotypes are made to identify the likely causes of flower abortion. The function of pollen derived from chilling sensitive plants is clearly affected most by low temperature stress, particularly the growth of the pollen tubes down the style before fertilisation occurs. In contrast, pollen tubes derived from chilling tolerant plants continue to grow down the style under low temperature stress. Although other stages of development and function were affected by low temperature, including sporogenesis, pollen germination, and the stigma, none were correlated to the phenotype of the mother plant. The implications of the findings for chickpea improvement programmes are discussed.     

Specific Spikelet Fertility as an Indicator of Cold Tolerance Identification at Booting Stage in Rice

Spikelet fertility is an uppermost evaluation indicator of cold tolerance in rice at the booting stage. Though many evaluation indicators have adopted by scientists, the whole spikelet fertility (SF) is one of the most important evaluation indexes under low- temperature stress conditions [1-3], which has practical significance in rice production. However, spikelets at different developmental stages have different sensitivities to low-temperature. Moreover, even within the same panicle the spi…     

不同时期干旱胁迫对水稻产量和生长特性的影响

为明确水稻生长过程中的水分敏感时期,探索水稻抵御干旱的栽培措施,以常规粳稻楚粳29号和云粳39号为材料,通过盆栽试验准确控制土壤水分(水势),研究不同时期干旱胁迫对水稻产量和生长特性的影响。结果表明,楚粳29号干旱胁迫处理较对照减产10.63%~47.60%,云粳39号干旱胁迫处理较对照减产6.19%~47.27%,减产程度依次为穗分化前期干旱胁迫(T2)﹥有效分蘖期干旱胁迫(T1)﹥穗分化后期干旱胁迫(T3)﹥孕穗期干旱胁迫(T4)。与对照相比,2个品种有效分蘖期干旱胁迫降低了有效穗数,穗分化前期干旱胁迫使每穗粒数明显减少,穗分化后期干旱胁迫使每穗实粒数减少和结实率明显降低,孕穗期干旱胁迫对结实率或千粒重有影响。     

土壤铜含量对水稻生长发育和产量形成的影响

 在盆栽土培条件下，以武香粳14号和汕优63为材料，研究了土壤铜含量对水稻生长发育和产量形成的影响。结果表明：(1) 土壤铜含量100、200 mg/kg处理对水稻株高、主茎总叶数、伸长节间数和抽穗期几乎没有影响，土壤铜含量达到400 mg/kg及其以上时，随着土壤铜含量的增加，水稻株高显著变矮、主茎总叶数和伸长节间数显著变少、抽穗期显著推迟；(2) 土壤铜处理使水稻产量显著低于CK，且随着土壤铜含量的提高水稻产量下降幅度显著增大；(3) 土壤铜含量100、200 mg/kg处理使水稻减产是由于每穗颖花数减少所致，土壤铜含量400 mg/kg及其以上处理使水稻减产是由于穗数和每穗颖花数共同减少所致；(4) 土壤铜处理使穗数减少主要是由于返青活棵慢、分蘖发生迟、高峰苗少所致，每穗颖花数减少主要是由于抽穗期单茎干物质量小和单位干物质量形成的颖花数少所致；(5) 随着土壤铜含量的增加水稻生物产量显著下降，经济系数呈下降趋势，但只有土壤铜含量达到800 mg/kg及其以上时经济系数才显著下降。     

Introduction of a fungal NADP(H)-dependent glutamate dehydrogenase (gdhA) improves growth,grain weight and salt resistance by enhancing the nitrogen uptake efficiency in forage rice

We report the effect of the introduction of a fungal glutamate dehydrogenase gene (gdhA) into forage rice (cv. Momiroman) by analyzing the transgenic rice plants in terms of growth, source function, and nitrogen contents. NADP (H)-dependent glutamate dehydrogenase activities in the gdhA-transgenic lines were markedly higher than those in non-transgenic control plants. Plant growth analysis at the seedling stage revealed that the leaf area and shoot and root dry weights of the high gdhA-expressors were higher than those of control plants under both high (high N) and low nitrogen (low N) conditions. These results suggested that the source ability was enhanced by the gdhA introduction. This was supported by the fact that the net photosynthesis rate at the heading stage was also higher in transgenic than in control leaves. Furthermore, under both high and low N conditions, the nitrogen contents in the shoots and roots, at seedling and grain-harvest stages, were significantly higher in high gdhA-expressors than in control plants, indicating that nitrogen uptake was higher in transgenic than in control plants. At the harvest stage, the high gdhA-expressors exhibited greater panicle and spikelet numbers per plant compared with control plants, resulting in higher grain weight, under the high N conditions. In addition, gdhA expression in forage rice significantly enhanced their tolerance to salt stress compared to control plants. The present study showed that the introduction of a fungal gdhA into forage rice could lead to higher source ability, better growth and higher grain weight by enhancing nitrogen uptake efficiency.     

Species,ecotype and cultivar differences in spikelet fertility and harvest index of rice in response to high temperature stress

Spikelet fertility (seed-set) is an important component of yield that is sensitive to high temperature. The objectives of this research were (a) to quantify the effects of high temperature on spikelet fertility and harvest index of rice; (b) to determine if there were species, ecotype, and/or cultivar differences in response to high temperature; and (c) to understand the reasons for lower and/or differential spikelet fertility and harvest index of rice cultivars at high temperatures. Fourteen rice cultivars of different species (Oryza sativa and Oryza glaberrima), ecotypes (indica and japonica) and origin (temperate and tropical) were exposed to ambient and high temperature (ambient + 5 °C) at Gainesville, Florida. High temperature significantly decreased spikelet fertility across all cultivars, but effects varied among cultivars. Based on decreases in spikelet fertility at high temperature, cultivar N-22 was most tolerant, while cultivars L-204, M-202, Labelle, Italica Livorna, WAB-12, CG-14 and CG-17 were highly susceptible and cultivars M-103, S-102, Koshihikari, IR-8 and IR-72 were moderately susceptible to high temperature. There were no clear species or ecotype differences, as some cultivars in each species or within ecotypes of tropical and temperature origin were equally susceptible to high temperature (for example M-202 temperate japonica, Labelle tropical japonica, CG-14 O. glaberrima, and WAB-12 interspecific). Decreased spikelet fertility and cultivar difference at high temperature were due mainly to decreased pollen production and pollen reception (pollen numbers on stigma). Lower spikelet fertility at elevated temperature resulted in fewer filled grains, lower grain weight per panicle, and decreased harvest index. There is a potential for genetic improvement for heat tolerance, thus it is important to screen and identify heat-tolerant cultivars. Spikelet fertility at high temperature can be used as a screening tool for heat tolerance during the reproductive phase.     

Impact of elevated CO2 concentration on inter-subspecific hybrid rice cultivar Liangyoupeijiu under fully open-air field conditions

Hybrid rice cultivar plays an important role in rice production system due to its high yield potential and resistance to environmental stress. Quantification of its responses to rising CO₂ concentration ([CO₂]) will reduce our uncertainty in predicting future food security and assist in development of adaptation strategies. Using free air CO₂ enrichment (FACE), we measured seasonal changes in growth and nitrogen (N) uptake of an inter-subspecific hybrid rice cultivar Liangyoupeijiu grown under two levels of [CO₂] (ambient and elevated by 200 μmol mol⁻¹) and two levels of N fertilization in 2005–2006. Average across the 2 years, FACE increased crop growth rate similarly by 22%, 24% and 23% in the periods from transplanting to panicle initiation (PI), PI to heading and heading to maturity, which was mainly attributed to an increase in green leaf area index rather than the greater net assimilation rate. Grain yield increased greatly under FACE as a result of similar contributions by panicle number per unit area, grain number per panicle and individual grain yield. Final aboveground N acquisition showed a 10.4% increase under FACE, which resulted from enhanced N uptake at both vegetative and reproductive growth stages. Compared with previous FACE studies on final productivity of two inbred japonica cultivars, inter-subspecific hybrid cultivar appears to profit more from elevated [CO₂], which mainly resulted from its greater enhancement in photosynthetic production during reproductive growth due to a lack of N limitations late in the season.     

Effect of intermittent irrigation following the system of rice intensification (SRI) on rice yield in a farmer’s paddy fields in Indonesia

System of rice intensification (SRI) has been disseminated in many countries because of its high yield, although the mechanism of yield increase has yet to be fully understood. The aims of this study were to clarify the actual water management of a skilled SRI farmer in irrigated paddy field of Indonesia and to examine the effect of intermittent water management on rice growth and yield. Yield and yield components were compared in the field experiments in the farmer’s fields under intermittent (SRI) or flooded (FL) irrigation for 4 years from 2013 to 2016. The daily mean water depth of SRI plots during 0–40 days after transplanting showed very shallow (ca. 2 cm) or little lower than soil surface and continued to be lower than soil surface during reproductive stage when panicles were formed. The yield of SRI significantly exceeded that of FL for 4 years by 13% (P?=?0.0004), so did the panicle numbers per area (P?=?0.036). The yield increase in SRI was associated with the increased number of panicles, which should have resulted from enhanced tiller development under shallow water level during the vegetative stage. The increased number of panicles was, however, counteracted by the reduced number of spikelets per panicle and resulted in nonsignificant increase in the spikelet density, defined as number of spikelets per unit area of crop. This dampening change in spikelet number per panicle could have been caused by limited supply of either nitrogen or carbohydrate during the panicle development stage under the intermittent water supply. A greater yield increase by SRI could be expected by improving nutrient or water management during the reproductive stage.     

Study of water stress effects in different growth stages on yield and yield components of different rice (Oryza sativa L.) cultivars

A field experiment was conducted during 2001-2003 to evaluate the effect of water stress on the yield and yield components of four rice cultivars commonly grown in Mazandaran province, Iran. In northern Iran irrigated lowland rice usually experiences water deficit during the growing season include of land preparation time, planting, tillering stage, flowering and grain filing period. Recently drought affected 20 of 28 provinces in Iran; with the southeastern, central and eastern parts of the country being most severely affected. The local and improved cultivars used were Tarom, Khazar, Fajr and Nemat. The different water stress conditions were water stress during vegetative, flowering and grain filling stages and well watered was the control. Water stress at vegetative stage significantly reduced plant height of all cultivars. Water stress at flowering stage had a greater grain yield reduction than water stress at other times. The reduction of grain yield largely resulted from the reduction in fertile panicle and filled grain percentage. Water deficit during vegetative, flowering and grain filling stages reduced mean grain yield by 21, 50 and 21% on average in comparison to control respectively. The yield advantage of two semidwarf varieties, Fajr and Nemat, were not maintained under drought stress. Total biomass, harvest index, plant height, filled grain, unfilled grain and 1000 grain weight were reduced under water stress in all cultivars. Water stress at vegetative stage effectively reduced total biomass due to decrease of photosynthesis rate and dry matter accumulation.     

不同光温反应型配组的籼粳交F1杂种优势的研究

 对早籼／早粳、早籼／中粳、早籼／晚粳、中籼／中粳和中籼／晚粳五种配组方式不完全双列杂交的杂种优势分析表明，株高、剑叶长、主穗长和主穗总粒数等性状的群体平均优势和群体超亲优势较强，Ｆ１性状平均基因型值预测认为，早籼／晚粳和中籼／晚粳杂种株高过高和抽穗偏迟，早籼／早粳配组生育期过短和穗小粒少，综合性状以中籼／中粳和早籼／中粳方式较为优良。Ｆ１性状间显性相关分析表明五种配组方式在株高、抽穗天数、剑叶长、主穗长和主穗总粒数五个性状间均存在显著的正相关，籼粳杂种表现的德大粒多同时伴有植株偏高、抽穗延迟和剑叶过披等倾向，但这种关联性在早籼／早粳或中籼／中粳配组中程度相对较低。