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.     

外源硅减轻高温引起的杂交水稻结实降低

选用硅酸钠(Na2SiO3·9H2O)为硅源,于大田条件下对耐热性不同的2个杂交水稻组合在拔节期连续3次喷施4个浓度水平(T-CK,0mmol/L;T-1.25,1.25mmol/L;T-2.50,2.50mmol/L;T-3.75,3.75mmol/L)的外源硅,研究施硅对花期自然高温和自然常温下杂交水稻柱头授粉性能、花药开裂性能和受精率的影响,并筛选适宜浓度的硅酸钠施用方案。结果表明,在田间高温条件下,与T-CK相比,施硅处理(T-1.25、T-2.50和T-3.75)使热敏感组合金优63和耐热组合汕优63的颖花受精率分别提高10.6和4.7百分点(绝对值);花药基部开裂宽度分别增加19.0%和10.3%(相对值);每柱头花粉萌发数增加16.9%和39.6%;授粉总数分别增加3.4%和30.5%;花粉萌发率上升11.3和7.0百分点;花粉萌发数大于10粒的小花的占比上升9.3和27.6百分点;花粉总数小于20粒的小花占比下降18.8和8.1百分点(相对值)。经对两个组合在常温和高温下施硅的花药发育及授粉特性的解析,初步认为外源硅对水稻授粉性能有综合提高作用,但比较而言,其作用可能主要与提高花粉发育质量有关,而提高授粉总数和改善花药裂药性能也有一定的辅助作用。此外,外源硅施用对高温敏感组合效果更佳,其适宜的喷施浓度为2.50mmol/L。     

Effect of Temperature on Pollen Fertility in Inter-Subspecific Rice Hybrids

Seventeen rice varieties and hybrids of different types (indica, japonica, javanica, indica hybrid, japonica hybrid and inter-subspecific hybrid) were evaluated to determine the effect of temperature on pollen fertility in inter-subspecfic hybrids. The pollen fertility of inter-subspecific hybrids was greatly reduced when average daily temperature dropped to 22.0 - 23.0℃at meiosis stage, and the extent of pollen fertility reduction varied greatly with respect to different hybrids. However, the pollen fertility reduction of indica and japonica hybrids and conventional varieties was not obvious under the same regime of temperature conditions. When the average daily temperature dropped to 20℃, the pollen development of conventional varieties and hybrids was also affected. Correlation analysis revealed that there existed a positive correlation between pollen fertility and average daily temperature. A significant difference (P<0.01) was also found between the two correlation coefficients i.e. inter-subspecific hybrids and conventional varieties. Temperature at meiosis stage of pollen mother cell was a key factor in pollen developing, and the pollen fertility of inter-subspecific hybrids was more sensitive to low temperature than that of traditional variety.     

Effects of the number of pollen grains on cold tolerance at the booting stage in rice lines with QTLs for cold tolerance

This study was conducted to clarify the relationship between the number of pollen grains per anther and spikelet fertility under low temperature conditions in the rice cultivars and lines including lines with quantitative trait loci (QTL) for cold tolerance, adapted to the Tohoku region of northern Japan. Cold-water treatment decreased anther length, the number of pollen grains per anther, and spikelet fertility in all cultivars and lines. The number of pollen grains was proportional to anther length in all cultivars and lines and under all temperatures. Spikelet fertility decreased with decreasing the number of pollen grains in cold-water treatments at 18.5 and 19.3?°C. ‘Ouu 415’, with the qLTB3 QTL for cold tolerance, had 28% more pollen grains and 9% higher spikelet fertility than the recurrent parent, ‘Hitomebore’, in the 18.5?°C cold-water treatment, suggesting that qLTB3 increased both parameters. Lines with the qCTB8 QTL for cold tolerance had significantly more pollen grains in two of the three years and significantly higher spikelet fertility in all three years in the 19.3?°C cold-water treatment, suggesting that qCTB8 reinforced cold tolerance. Ctb1, a proposed cold-tolerance QTL, had no effect on the number of pollen grains or spikelet fertility. In conclusion, the cultivars and lines with more pollen grains had a higher cold tolerance. Some of QTLs were inferred to increase the number of pollen grains and reinforce cold tolerance.     

在蒙导条件下转bar基因水稻与无芒稗间的基因漂移

以转基因水稻Y0003和99-t为父本,无芒稗为母本,在蒙导条件下研究转基因水稻与无芒稗间潜在的基因漂移可能性。用光学显微镜观察了用不同方法（紫外灯照射,反复冻融,黑暗放置）制备的蒙导花粉蒙导条件下转基因水稻花粉在无芒稗柱头上的萌发生长情况,并与无芒稗自花授粉的情况相比较。结果表明,在供试的所有蒙导花粉蒙导条件下,两种转基因水稻的花粉在无芒稗柱头上虽能萌发,但花粉管扭曲成各种形状而不能进入无芒稗柱头。与无芒稗自花授粉的花粉萌发生长有极明显的差异。杂交也不结实。说明蒙导花粉不能克服转基因水稻和无芒稗的不亲和性,转基因水稻与无芒稗间基因漂移的可能性极小。     

Breeding lines with neutral genes to improve fertility of intersubspecific hybrid rice

Since the sterility neutral allele S5n has been incorporated into indica or japonica varieties, many intersubspecific hybrids have been released commercially. These hybrids showed high heterosis, but some of them exhibited unstable seed setting rate under low temperature.When the hybrids flowered at low temperature, the fertility of female gamete was normal but the pollen showed sterile. To improve the stability of fertility, the effect of pollen sterility neutral gene was studied for intersubspecific hybrids.     

温光敏核不育小麦C338S的育性表现及不同蘖位和花位的育性差异

为了解温光敏核不育小麦不同播期及不同蘖位、花位的育性变化,通过多年分期播种试验,研究了小麦温光敏细胞核雄性不育系C338S不同播期下的育性表现及不同蘖位和花位的育性差异。结果表明,随着播期的调整,C338S分别表现完全不育、高度不育、半不育、低不育、可育的不同育性状态,具有育性转换特性。主茎穗与分蘖穗之间、主茎穗不同部位的小穗之间以及不同位次的小花之间的育性存在差异。发育较晚的后生分蘖的育性高于主茎穗和早生分蘖;主茎穗的下部小穗育性>中部小穗>上部小穗;早播不育植株发育较晚的3、4位小花的育性较好,而晚播可育植株发育较早的1、2位小花的育性较高。     

光敏核不育水稻育性转换条件及其生态适应性研究（英文）

 本文系统介绍了诱导光敏核不育水稻育性转换的光温作用模式的内容和意义,认为光敏核不育水稻育性转换的光周期诱导,只能在一定的温度范围内才存在。讨论了诱导光敏核不育水稻育性转换的光周期敏感期、光照长度、光照强度及曙暮光影响、光期暗期与光质的影响,分析了温度的作用、温度影响的敏感期与温度分解因子的影响;并对现有不育系的生态类型和适应性作了初步分析。     

Seed-set and pollen–stigma compatibility in Leymus chinensis

Chinese leymus [Leymus chinensis (Trin.) Tzvel.] is an important forage distributed in East Asia. The seed‐set rates and the pollen–stigma compatibility in six populations were investigated in 2001. Proportionately seed‐set ranged from 0·065 to 0·567 under open pollination and 0·0056 to 0·0426 under self‐pollination. The former is significantly higher than the latter in each population. Microscopic observations showed that proportionately only 0·0551 to 0·1167 of self‐pollinated pollen grains were compatible but most cross‐pollinated pollen grains were compatible. The tubes of most incompatible pollen grains aborted upon entering into the stigmas. Among the six populations, there was a significant correlation between seed‐set under open pollination and the compatible pollen rates under cross‐pollination. These results suggest that Chinese leymus is a self‐incompatible species, and the compatibility of pollen and stigma might be one of the factors influencing seed‐set in natural conditions. This information will be useful for future breeding efforts.     

海南普通野生稻的花粉育性观察及杂交亲和性

对海南3个不同居群的普通野生稻(O.rufipogon Griff.)的花粉育性进行了观察研究,并采用荧光显微镜技术观察了转基因水稻花粉在不同居群的普通野生稻柱头上的萌发和在花柱内的生长过程。结果表明,以转基因水稻为对照,3个不同居群的野生稻相互之间花粉可育率在1%水平上差异极显著。用荧光显微镜观察时发现,转基因水稻花粉能在3个居群的普通野生稻的柱头上萌发并能到达胚珠,二者杂交亲和,同时发现,花粉管进入三亚居群胚珠的数目比儋州、万宁居群的数目多,说明相对于儋州、万宁居群来说,三亚居群与转基因水稻的杂交亲和性更高。     

叶枕距标记法研究低温对粳型光温敏核不育系育性转换的影响

用日均温20℃低温处理3个采用剑叶叶枕距标记幼穗发育时期的粳型光温敏核不育系G317S、G321S和G326S,研究低温对不同发育时期粳型光温敏核不育系育性的影响.结果表明:用20℃低温处理3d,3个粳型光温敏核不育系花粉不育度明显降低,平均自交结实率为66.41％;3个粳型光温敏核不育系育性敏感期所对应的剑叶叶枕距为-4 ～4 cm,而剑叶叶枕距＜-4 cm或＞4 cm时,各不育系育性稳定;剑叶叶枕距为-4～ -2 cm和2～4 cm时各不育系不同穗位颖花的花粉不育度比较接近,而剑叶叶枕距为-2～2 cm时,各不育系不同穗位颖花的花粉不育度表现为穗上部＜穗中部＜穗下部.     

敲除TMS5基因获得温敏不育粳稻新材料

【目的】水稻温敏不育系的选育是两系杂交稻育种工作中的关键环节。TMS5是控制温敏不育的重要基因,在生产上也应用较广。为了加快水稻温敏不育系的选育进程,【方法】利用CRISPR/Cas9技术,在武运粳7号背景下对TMS5基因进行编辑。【结果】通过测序从22株T0代中筛选获得6株纯合的突变体,分析发现6个纯合的突变体产生了相同的遗传变异,都在TMS5基因第2外显子44 bp和45 bp之间插入碱基"A",导致翻译提前终止。通过细胞学观察和人工辅助授粉证实获得的株系花粉败育而雌配子正常发育。【结论】这些结果表明对温敏不育基因TMS5基因进行编辑可以快速获得粳型温敏雄性不育系。     

Heat-Induced Floret Sterility of Hybrid Rice (Oryza sativa L.) Cultivars under Humid and Low Wind Conditionsin the Field of Jianghan Basin,China

Abstract

Projected global warming is expected to increase the occurrence of heat-induced floret sterility (HIFS) in rice. However, there are few field-scale studies that could aid in predicting the potential risks to rice yield and developing countermeasures against yield losses. The aim of this study was to elucidate the factors that induce floret sterility under high temperature conditions during the flowering season in the field condition in China. Studies were conducted in irrigated paddy fields with the regional hybrid-rice cultivars grown in Jianghan Basin where air temperature is not so high during the flowering season but HIFS frequently occurs. The microclimate, panicle temperature, floret sterility, pollination, and size of dehiscence formed at the base of anthers were investigated. Significant losses in seed set were observed under the high temperature condition. Although the maximum atmospheric temperature was approximately 35ºC, the relative humidity was very high (around 70% at the time of maximum temperature), with low wind speeds, occasionally below 1 m s¹. Under such conditions sunlit panicle temperature exceeded atmospheric temperature by as much as 4ºC. Moreover, the anthers of some cultivars exhibited short basal dehiscence, and the dehiscence length was positively correlated with the percentage of sufficiently pollinated florets (r=0.859, P<0.05, n=7) and with seed set (r=0.827, P<0.05, n=7) across the cultivars. The results suggest that the combination of hot, humid, and windless climatic conditions with short basal dehiscence of anthers induces HIFS in hybrid rice grown in this region.     

敲除TMS5基因获得温敏不育粳稻新材料

【目的】水稻温敏不育系的选育是两系杂交稻育种工作中的关键环节。TMS5是控制温敏不育的重要基因，在生产上也应用较广。为了加快水稻温敏不育系的选育进程，【方法】利用CRISPR/Cas9技术，在武运粳7号背景下对TMS5基因进行编辑。【结果】通过测序从22株T0代中筛选获得6株纯合的突变体，分析发现6个纯合的突变体产生了相同的遗传变异，都在TMS5基因第2外显子44 bp和45 bp之间插入碱基“A”，导致翻译提前终止。通过细胞学观察和人工辅助授粉证实获得的株系花粉败育而雌配子正常发育。【结论】这些结果表明对温敏不育基因TMS5基因进行编辑可以快速获得粳型温敏雄性不育系。     

Research Progress on Heat Stress of Rice at Flowering Stage

Global warming has caused frequent occurrence of heat stress at the flowering stage of single-season rice in the Yangtze River region of China, which results in declines of spikelet fertility and yield in rice. Rice flowering stage is the most sensitive period to high temperatures, and therefore, the key for heat stress happening is the flowering stage coinciding with high temperature, which causes spikelet fertility decreasing in heat-sensitive varieties, and is the major factor for heat injury differences among various rice planting regions. With the development of rice breeding, temperature indexes for heat stress has been converted from daily maximum temperature of 35 °C to 38 °C with the stress duration of more than 3 d. During the flowering stage, anther dehiscence inhibition and low pollen shedding onto the stigma are two main reasons for spikelet fertility reduction under high temperatures. At panicle initiation stage, high temperatures aggravate spikelet degeneration, and destroy floral organ development. Various types of rice varieties coexist in production, and indica-japonica hybrid rice demonstrates the highest heat resistance in general, followed by indica and japonica rice varieties. In production, avoiding high temperature is the main strategy of preventing heat stress, and planting suitable cultivars and adjustment of sowing date are the most effective measures. Irrigation is an effective real-time cultivation measure to decline the canopy temperature during the rice flowering stage. We suggested that further study should be focused on exploring heat injury differences among different rice variety types, and innovating rice-planting methods according to planting system changes in rice planting regions with extreme heat stress. Meanwhile, high temperature monitor and warning systems should be improved to achieve optimal heat stress management efficiencies.     

温度对亚种间杂种花粉育性的影响

以17个不同类型的籼、粳、爪哇型品种及其杂种为材料,通过分期播种,研究了温度变化对花粉育性的影响。结果表明,当花粉母细胞减数分裂期的日平均气温低于22~23℃时,亚种间杂种的花粉育性显著降低,不同组合花粉育性存在明显差异,而品种间杂种和常规品种的花粉育性受影响较小;当花粉母细胞减数分裂期的日平均气温低于20℃时,常规品种和品种间杂种的花粉发育也受到不同程度的影响,不同品种与组合间存在差异。花粉母细胞减数分裂期的日平均温度与花粉育性的相关性分析表明,温度与花粉育性呈显著正相关,亚种间杂种与常规品种的相关系数存在极显著差异。说明减数分裂期的花粉育性受温度影响,温度对亚种间杂种花粉育性的影响较常规品种大。关键词     

Correlation and Regressive Model Between Spikelet Fertilized Rate and Temperature in Inter-Subspecific Hybrid Rice

To study the sensitivity of inter-subspecific hybrid rice to climatic conditions, the spikelet fertilized rate (SFR) of four types of rice including indica-japonica hybrid, intermediate hybrid, indica and japonica were analyzed during 2000-2004. The inter-subspecific hybrids showed lower SFR, and much higher fluctuation under various climatic conditions than indica and japonica rice, showing the inter-subspecific hybrids were sensitive to ecological conditions. Among 12 climatic factors, the key factor affecting rice SFR was temperature, with the most significant factor being the average temperature of the seven days around panicle flowering (T7). A regressive equation of SFR-temperature by T7, and a comprehensive synthetic model by four important temperature indices were put forward. The optimum temperature for inter-subspecific hybrids was estimated to be 26.1-26.6℃, and lower limit of safe temperature to be 22.5-23.3℃ for panicle flowering, showing higher by averagely 0.5℃ and 1.7℃, respectively, to be compared with indica and japonica rice. This suggested that inter-subspecific hybrids require proper climatic conditions. During panicle flowering, the suitable daily average temperature was 23.3-29.0℃, with the fittest one at 26.1-26.6℃. For an application example, optimum heading season for inter-subspecific hybrids in key rice growing areas in China was as same as common pure lines, while inferior limit for safe date of heading was about a ten-day period earlier than those of common pure lines.     

两系杂交稻杂种低温下育性稳定性的初步研究

考察了水稻常规品种及两系杂交稻在低温影响后的花粉育性变化。结果表明：ａ）低温是影响水稻常规品种育性稳定性的重要生态,且受低温影响后不同品种表现出育性稳定性的明显差异;ｂ）在常温下杂种Ｆ１均能基本恢复正常可育,但在低温下Ｆ１的花粉育性都有所下降,且下降幅度在组合间差异明显;ｃ）Ｆ１的育性的稳定性与父本对低温的敏感程度有关;ｄ）母本对Ｆ１的育性稳定性也有重要影响。     

The Early-Morning Flowering Trait of Rice Reduces Spikelet Sterility under Windy and Elevated Temperature Conditions at Anthesis

Abstract

We previously demonstrated that heat-induced spikelet sterility at anthesis could be mitigated by using an early-morning flowering (EMF) line of Oryza sativa L. cv. Koshihikari crossed with wild rice, O. officinalis. Another microclimate factor, high wind velocity, is known to increase the sterility induced by heat. In this study, we evaluated whether EMF rice could mitigate sterility under the combined stresses of heat and wind. Rice plants were exposed to three levels of wind velocity (1.1, 2.2, 3.4 m s^?1) from early-morning until 1500 in a glasshouse, where air temperature reached 30°C at 0800, 34°C at 1000 and 38°C around noon. Under these conditions, sterility steadily increased in Koshihikari, ranging from 28.4 to 86.9% as wind velocity increased. However, in the EMF line, low levels of sterility were observed since most spikelets flowered before 1000 when air temperature reached 35°C, the critical value for causing sterility. These results indicated that the increase in heat-induced spikelet sterility by wind can be potentially mitigated by using EMF rice.     

光敏核不育水稻在寒冷稻作区的育性转换特性及开花习性

光敏核不育水稻(PGMR)的发现与深入研究给杂交粳稻的发展带来了新的途径,但易受气候条件影响的特点又制约了其应用的范围。因此,为了采用相应的育种手段在寒冷稻作区利用这种资源,尚需进一步弄清其在本生态区的表现特点。本文的目的是通过观察31116S等代表性的粳型PGMR的育性转换特性和开花习性,为有效地将其应用于寒地杂交粳稻的选育提供参考资料。1 材料与方法1989年自辽宁、武汉等地引入31116S、N5047S、6085S、6283S等4份有代表性的粳型PGMR,并经海南自交繁殖,1990年在吉林省农科院水稻试验田(43°31′N)分期播种(表1)。并以31116S为试材,每隔3～4d播种一批(图1),4叶1心时移栽大田,株行距13.3cm×30cm,3行区,每行20株。以31116S、N5047S、6085S、6283S为材料,设置13.0、13.5、14.0、14.5、15.0h 5种不同光照时间处理。具体做法是每处理用塑料槽种30株,株行距10cm×20cm,同一光长处理的不同材料种植于同一槽内,用3层黑布遮光严密。以上各不同处理在抽穗期用I_2-KI染色观察20个