1‐Methylcyclopropene (1‐MCP)‐Induced Alteration in Leaf Photosynthetic Rate,Chlorophyll Fluorescence,Respiration and Membrane Damage in Rice (Oryza sativa L.) Under High Night Temperature

High night temperature (HNT) can induce ethylene‐triggered reactive oxygen species production, which can cause premature leaf senescence and membrane damage, thereby affecting production, consumption and transfer of photosyn‐thates, and yield. The 1‐methylcyclopropene (1‐MCP) can competitively bind with ethylene receptors and decrease ethylene effects. The objective was to determine the effects of HNT and 1‐MCP on leaf photosynthetic rate (P_N), chlorophyll fluorescence, total chlorophyll (TC), respiration, membrane damage, pollen germination, spikelet fertility (SF) and yield of rice hybrid ‘XL723’. Plants were grown under ambient night temperature (ANT) (25 °C) or HNT (30 °C) with or without 1‐MCP treatment. Application of 1‐MCP was at the boot stage. The decrease in yield (11 %) under HNT was associated with decreased P_N (4 %), stomatal conductance (8 %), quantum yield (11 %) TC (23 %) and SF (5 %) and increased respiration (74 %), F_o/F_m (increase in thylakoid membrane damage; 11 %) and membrane damage (leaf electrolytic leakage; 57 %). The 1‐MCP‐treated plants grown under HNT showed increased yield (17 %), which was associated with increased P_N (10 %), stomatal conductance (30 %), quantum yield (9 %), TC (37 %) and SF (11 %) and decreased respiration (39 %), F_o/F_m (5 %) and membrane damage (18 %). Plants grown under HNT showed increased grain chalkiness (154 %) compared with plants grown under ANT.     

Effects of Elevated Ultraviolet-B Radiation on Productive Tillers, Spikelet Sterility and Grain Characteristics of Southern US Rice (Oryza sativa L.) Cultivars

Depletion of the stratospheric ozone layer is leading to an increase in ultraviolet-B (UVB) radiation (280–320 nm) reaching the Earth's surface, which can alter crop productivity. The objective of this study was to determine the effects of elevated UVB radiation on rice production with special emphasis on grain characteristics in southern US rice cultivars (six inbred cultivars and three hybrids). Due to the spectral characteristics of the greenhouse glass, plants received no natural UVB radiation; hence, plants were provided with supplemental UVB lighting. Plants were exposed to UVB radiation of 0, 8 (ambient) or 16 (twice ambient) kJ m⁻² day⁻¹. There was no significant effect of elevated UVB radiation on the number of productive tillers in any cultivar except 'Sierra'. All the cultivars except 'Sierra' showed increased spikelet sterility with an increase in UVB radiation. There were decreases in main-stem panicle length, number of primary branches per panicle, and grain width with an increase in UVB radiation in most of the inbred cultivars. Elevated UVB radiation decreased plant grain yield in all the cultivars, however the per cent decrease in plant grain yield varied among the cultivars (31–79 %). The hybrid 'Clearfield XL729' performed best among the selected southern US rice cultivars under an elevated UVB environment.     

水稻内源油菜素甾醇对施氮量的响应及其对颖花退化的调控作用

为探明油菜素甾醇(brassinosteroids,BRs)是否介导氮肥对水稻颖花退化的影响。水稻品种扬稻6号和甬优2640种植于盆钵,全生育期设置3种施氮水平,观察了不同氮肥处理下水稻减数分裂期幼穗中氮含量、BRs、过氧化氢(H2O2)和总抗氧化能力(totalantioxidantcapacity,T-AOC)水平及其与颖花退化的关系。结果表明,颖花退化率的降低与稻穗中增加的24-表油菜素甾酮(24-epicastasterone,24-epiCS)和28-高油菜素内酯(28-homobrassinolide,28-homBL)含量密切相关。当稻穗的氮含量为1.25%时,幼穗中BRs(24-epiCS和28-homBL)含量显著增加,颖花退化率显著降低。稻穗中T-AOC水平与BRs含量变化趋势相同,且均与水稻颖花退化率显著负相关,而H_2O_2含量与BRs含量和T-AOC变化趋势相反。施用外源BRs(24-epiCS或28-homBL)可显著提高稻穗中内源BRs(24-epiCS和28-homBL)含量与T-AOC水平,并显著降低稻穗中H_2O_2含量和颖花退化率,施用BRs合成抑制剂则效果相反。表明BRs可以介导氮肥对水稻颖花退化的调控,在减数分裂期适宜的稻穗含氮量(1.25%)可有效提高幼穗中的BRs含量,并通过提高抗氧化能力来抑制颖花退化。     

Responses of spikelet fertility to air,spikelet, and panicle temperatures and vapor pressure deficit in rice

High temperature-induced spikelet sterility is expected to become a major factor reducing rice yield under the future climate conditions. To examine the responses of spikelet sterility to air temperature, humidity, and temperatures of panicle and spikelet, two japonica rice cultivars in different maturity groups were exposed to four sets of different temperature conditions from initial heading stage in 2013 and 2014. The temperature conditions included ambient temperature (AT), AT + 1.5°C, AT + 3.0°C, and AT + 5.0°C. Spikelet fertility showed a wide range of variation from 100 to 4.6% depending on temperature treatments. The ridge regression revealed that not only air temperature but also vapor pressure deficit (VPD) was negatively associated with spikelet fertility. The spikelet fertility was well fitted to logistic equations not only of air temperature, spikelet internal temperature, and panicle surface temperature but also of VPD. No clear difference in the accuracy of sterility estimation was observed for models that use air temperature, panicle or spikelet temperature as inputs. In contrast, the logistic equation model that uses both air temperature and VPD as independent variables had better accuracy in predicting spikelet sterility. These results suggested that spikelet or panicle temperature would be no better predictor for high temperature-induced spikelet sterility than air temperature. Therefore, further study is merited to verify the VPD effects on spikelet sterility under high temperature conditions.     

Effects of Increasing Temperatures on Spikelet Fertility in Different Rice Cultivars based on Temperature Gradient Chamber Experiments

Spikelet sterility in rice (Oryza sativa L.) induced by high temperatures is a major concern given global warming predictions. We studied differences among eight rice cultivars in spikelet fertility at five different temperature levels in temperature gradient chamber (TGC) experiments. Six japonica and two indica cultivars were exposed to high‐temperature gradients in TGCs during the 2005 flowering season. Spikelet sterility increased with temperature in TGCs and differed among cultivars because of both variations in temperature tolerance and timing of heading. The correlation between spikelet fertility of individual panicles and both air temperature and panicle temperature during flowering was analyzed to compare tolerances among cultivars. The temperature (T₇₅) at which spikelet fertility was 75 % of maximum ranged from 34 to 39 °C air temperature and differed significantly among cultivars. Indica varieties had higher T₇₅ values than japonica varieties. The T₇₅ values based on panicle temperature also differed among cultivars, but the difference between indica and japonica varieties were less significant. We concluded that the higher temperature tolerances of indica cultivars in our experiments could be attributed to lower spikelet temperatures, and cultivars with similar spikelet temperatures still had different heat tolerances due to differences in pollination ability.     

Evaluation of Upland Rice (Oryza sativa L.) Genotypes for Intercropping with Pigeon Pea (Cajanus cajan [L.] (Mill sp.))

Eleven upland rice genotypes of varying growth duration and plant stature were evaluated in two cropping systems: monocrop and intercrop, with pigeon pea cv. U pas 120, in order to study the effects of intercropping on rice grain yield and its contributing characteristics during 1990 to 1992 wet seasons. Cropping system and cropping system × genotype interaction effects were significant for yield ha⁻¹, panicle weight, panicles m⁻² and spikelet fertility suggesting the need for evaluating and selecting genotypes suitable for intercropping. Rice grain yield reduction in the intercrop ranged from 24.5 % in genotype RR 203-16 to 54.5 % in genotype Aditya. Panicle weight, total dry matter at flowering as well as at harvest, and harvest index were also reduced. Plant height and panicle weight were positively associated with yield in both systems, however, the yield was positively and significantly correlated with spikelets per panicle and spikelet fertility with the intercropping system. The correlation between cropping systems indicated the possibility of simultaneous improvement for these characteristics in monocropping and intercropping.     

Development of TGMS lines for developing two-line rice hybrids for the tropics

A breeding program was initiated at the International Rice Research Institute (IRRI) in 1990 to develop thermosensitive genic male sterile (TGMS) rice lines for developing two-line rice hybrids for the tropics. The TGMS trait was transferred from a temperate japonica TGMS mutant, Norin PL 12, to indica and tropical japonica rice varieties using the pedigree selection procedure. Six new TGMS rice lines adapted to tropical conditions were developed which showed complete pollen and spikelet sterility when maximum temperature was higher than 30 ^°C 1–2 week after panicle initiation. However, up to 85.5% spikelet fertility was observed when these lines were exposed to 26–29 ^°C during the critical stage. Using two of these TGMS lines, some heterotic rice hybrids showing 1–1.6 t/ha higher grain yield than the inbred check varieties were identified in unreplicated observational yield trial conducted at IRRI. Two of the six two-line hybrids yielded significantly higher than the check variety in a replicated preliminary yield trial. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mapping quantitative trait loci influencing panicle‐related traits from Chinese common wild rice (Oryza rufipogon) using introgression lines

Panicle‐related traits are important agronomic traits which directly associated with grain yield. In this study, we investigated quantitative trait loci (QTLs) associated with panicle‐related traits using a set of 265 introgression lines (ILs) of common wild rice (Oryza rufipogon Griff.) in the background of Indica high‐yielding cultivar Guichao 2 (O. sativa L.). A total of 39 QTLs associated with panicle‐related traits including panicle length (PL), primary branch number (PBN), secondary branch number (SBN), spikelet number per panicle (SPP) and spikelet density (SD), were detected in the ILs with single‐point analysis. The alleles of 20 QTLs derived from wild rice showed positive effects, and some QTLs, such as, QPl1b for PL, QPbn8 for PBN, QSd4 and QSd11b for SD and QSpp4 for SPP showed larger positive effects, providing good candidates and useful information for marker‐aided improvement of yield potential of rice. Most of the QTLs controlling SPP, SBN and SD were located in cluster or closely linked on chromosomes, and the directions of their additive effects were consistent, which explained the genetic basis of significant correlations between their phenotypic characters.     

Mapping and candidate gene analysis for a new top spikelet abortion mutant in rice

Grain numbers is one of the determinations for rice yield and directly associated with spikelet numbers per panicle and its normal development. Lots of genes responsible for spikelet numbers and spikelet early development have been identified, but the molecular information about the spikelet development at later development is still limited. Here, we isolated a rice spikelet abnormal development mutant, which shows degenerated spikelet at the top panicle and named aborted top spikelet mutant 1(Ats1). The spikelets derived from the middle and bottom branches per panicle of Ats1 show normal development with those of wild type. However, a large number of branches and spikelets with arrested development were often observed only on apex panicle. The abnormality did not appear until the stage In8 when rachises elongate rapidly and reproductive organs get mature, based on observations through SEM analysis. The aborted spikelet could develop the complete floral organs with a pair of rudimentary glume, a pair of empty glume, two lodicule, six stamens and one carpel. But all these floral organs did not develop maturity. Genetic analysis on two F₂ populations indicated that the Ats1 was controlled by a single dominant gene. By using bulked segregant analysis of F₂ population developed from Ats1 crossing with Songjing6, ATS1 was mapped on chromosome 8 between RM3819 and RM5556. Then, the fine mapping was performed with 1078 F₂ population developed from Ats1 and IR36. The ATS1 locus was finely mapped in an 85.7 kb region between RM22448 and STS8‐2 with 8 genes according to the rice annotation project database. Sequence analysis of the candidate genes within the delimited region of the Ats1 and Akihikari showed two‐nucleotide changes, including single‐nucleotide substitutions corresponding to an amino acid substitution from asparagine to lysine acid in exons 3 and a 1‐bp deletion resulting in a premature stop codon in exon 22 at the candidate gene, LOC_Os08g06480. A cleaved amplified polymorphic sequence (CAPS) marker, CAPS‐ats1, was developed from the 1‐bp deletion site. The complete cosegregation of the CAPS genotypes with the matching phenotypes were observed in the F₂ populations. This suggested that Os08g06480 is most likely the ATS1 gene. These results will provide more information for better understanding of the molecular mechanism governing top spikelet abortion within a short developmental period.     

Agro-morphological characterization of ovary culture-derived plants of rice (Oryza sativa L.)

Plants derived from unpollinated ovary culture of ten rice genotypes showed significant variability in agro-morphological characteristics. The ovary-derived plant (H1) populations were completely haploid, doubled haploid or haploid-doubled haploid mixture. Haploids had very drastic reduction in plant height, panicle length, grain length, breadth and number and spikelet fertility (0.0%–2.1%). Doubled haploids from the hybrid of UPRI 95–121 × UPRI 95–165 were normal with fertility ranging between 69.6% and 97.7%. A genetic segregation in ratio of 1:1 was observed for five pigmentation characters in the H1 population derived from hybrid UPRI 95–122 × UPRI 95–165. Plant height showed the largest coefficient of variability (28.5%) followed by the number of spikelets per panicle (24.2%), number of grains per panicle (22.0%), percent seed set (9.2%) and panicle length (9.0%). The range of variation in the H1 population from fully fertile hybrid PMS 2A (CMS) × IR 31802 (restorer) was similar to its corresponding F2 population for plant height, spikelet fertility and number of grains/panicle. A single clone of plants from the cultivar BG 1321 exhibited complete male sterility but normal female fertility when pollinated with other varieties. Ovary-derived plants from the CMS lines PMS 2A and IR 58025A showed stable male sterility and those from thermosensitive genetic male sterile line UPRI 95–140 showed thermosensitive genetic male sterility. These lines have potential in the hybrid breeding program and are being currently exploited. This revised version was published online in July 2006 with corrections to the Cover Date.     

增加穗粒数的水稻染色体代换系Z747鉴定及相关性状QTL定位

增加穗粒数对水稻高产品种培育至关重要。其遗传基础复杂,由多基因控制。水稻染色体片段代换系可以将多基因控制的复杂性状分解,因而是理想的遗传研究材料。本研究通过高代回交和自交结合分子标记辅助选择方法,鉴定了一个以日本晴为受体、西恢18为供体亲本的、含有15个代换片段的增加穗粒数的水稻染色体片段代换系Z747,平均代换长度为4.49 Mb。与受体日本晴相比, Z747的每穗总粒数、一次枝梗数、二次枝梗数、穗长和粒长显著增加,粒宽显著变窄、结实率显著降低,但结实率仍为81%。进一步以日本晴和Z747杂交构建的次级F2群体鉴定出46个相关性状的QTL,分布于水稻1号、2号、3号、5号、6号、9号、11号和12号染色体上。其中qGPP12、qPH-3-1、qPH-3-2等12个QTL可能与已克隆的基因等位, qSPP9等34个可能是新鉴定的QTL。Z747的每穗总粒数由2个具有增加粒数效应的QTL (qSPP3和qSPP5)和1个具有减少粒数效应的QTL (qSPP9)控制。研究结果对主效QTL的精细定位和克隆、以及有利基因的单片段代换系培育有重要意义。     

IRRI新株型稻每穗颖花数与茎秆性状的遗传相关和通径分析

对IRRI25个新株型稻品种的每穗颖花数与10个茎秆性状进行相关和通径分析，结果表明：每穗颖花数与第1、2、4节间、长、茎粗、秆型指数和着粒密度呈显著或极显著的相关关系，且这些性状对每穗颖花数的通径系数也较大，在育种上，要提高每穗颖花数需要增加第1、2节间长度、茎粗、秆型指数，缩短第4、5节间长度。     

氮素穗肥运筹方式对杂交晚粳稻产量和品质的影响

为探明优质杂交粳稻在双季稻区种植的适宜穗肥运筹方式,以杂交粳稻申优26为材料,设置4种穗肥运筹方式（SF0,不施穗肥;SF1,倒2叶期施穗肥60kg/hm²;SF2,倒4叶期施穗肥60kg/hm²;SF3,倒2叶、倒4叶期分别施穗肥30kg/hm²）,以SF0为对照,研究不同氮素穗肥运筹方式对杂交粳稻在双季稻区种植产量和米质的影响。结果表明,与SF0处理相比,SF1、SF2和SF3处理干物质量、总颖花量和收获指数提高,产量分别增加10.88%、11.08%和12.73%。SF2和SF3处理总颖花量和表观转化率高于SF1处理,花后干物质生产比例低于SF1处理。与SF0处理相比,各穗肥运筹处理的加工品质变优,粗蛋白含量增加,而外观品质和蒸煮食味品质变差,食味值下降;此外,峰值黏度和崩解值也有所降低,但SF2与SF0处理无显著差异。总体上,SF2处理各品质指标优于SF1和SF3处理,施用穗肥可显著增加优质杂交粳稻产量,于倒4叶期施用一次穗肥能兼顾高产和优质。     

Phenotypic and genotypic variation in seed production traits within a full-sib family of meadow fescue

Phenotypic and genotypic variation for seed yield and associated traits (heading date, plant height, number of fertile tillers, 1000‐seed weight, panicle length, seed weight per panicle, fertility, flag‐leaf length and flag‐leaf width) were studied in a full‐sib family of meadow fescue using replicated clonal trials at two locations in Norway. Genotypic variances were highly significant for all traits and genotype × location interactions were significant for heading date, number of fertile tillers and seed yield. Seed yield and other seed component traits exhibited the largest genotypic variations. Heading date showed large genotype × location interaction, probably because of the very diverse origin of the two parents of the full‐sib family. Path coefficient analysis showed that panicle fertility, measured as seed weight per unit length of panicles, was by far the most important component trait contributing to seed yield, followed by the number of fertile tillers, plant height and flag‐leaf width. Flag‐leaf width and plant height had sizeable indirect effects on seed yield via panicle fertility. This is the first time that the importance of the size of the flag leaf for seed yield in herbage grasses has been demonstrated.     

籼稻粒形及产量性状的加性相关和显性相关分析

以８个粗短粒品种和５个细长粒品种进行不完全双列杂交，采用加显遗传模型，对早籼粒形及产量性状进行多种相关分析。结果表明农艺性状间的加性相关比显性相关更为重要，其中粒形性状间的遗传相关是以加性相关为主，仅粒宽与长宽比性状间同时存在着显著的显性相关。有效穗数与着粒密度、每穗粒数、穗重间具有较高的负向加性相关，与粒重则表现出明显的正向显性相关。着粒密度、每穗粒数、结实率、穗重、粒重以及单株产量性状间的相关     

水稻穗结构的定量特征与虚拟表达的初步研究

连续观察了不同品种和不同氮肥处理条件下水稻穗结构,并对其进行了定量分析及参数化处理。结果表明,一次枝梗长与穗长之比随穗轴节位呈两次函数变化,不同品种类型之间的参数变异较大;一次枝梗上的二次枝梗数与一次枝梗长度呈线性变化;一次枝梗基本均匀着生于穗轴上,一次枝梗和二次枝梗的节间距离变化不大。进一步利用水稻生长模型输出的穗粒数和一次枝梗数分析了二次枝梗的空间分布。最后结合上述结构特征,进行了水稻穗结构的计算机模拟。     

简化施肥对免耕冬水田不同杂交中稻/再生稻产量的影响

为探明免耕冬水田条件下简化施肥对不同杂交稻品种头季、再生季以及两季产量的影响,以及筛选出两季高产品种应用于生产。2016—2017年,以18个杂交中稻品种为材料,在免耕冬水田施纯氮120 kg/hm²条件下,设置简化施肥（一次基施N）和常规施肥（基肥：蘖肥：穗肥=5:3:2比例平衡施N）2种氮肥管理方式,研究其对中稻-再生稻产量的影响。结果表明,2种氮肥管理方式对头季产量、再生季产量和两季总产的影响均未达到显著水平,简化施肥处理的头季稻产量、再生季产量和两季总产分别为9.46 t/hm²、1.50 t/hm²和10.96 t/hm²,较常规施肥处理的产量分别增加1.40%,-6.77%和0.20%。18个品种间头季产量、再生季产量和两季总产差异均达极显著水平,18个品种头季、再生季和两季总产的产量变幅分别为8.70~10.19 t/hm²,0.59~2.29 t/hm²和10.21~11.57 t/hm²。头季产量和再生季产量呈极显著负相关(r=0.61)。两季总产与头季有效穗、每穗颖花数、结实率、千粒重和再生季有效穗偏相关系数均达极显著水平,并建立回归方程。因此,采用一次基施的简化施肥方式是免耕冬水田水稻实现高产、省工的有效途径,选择穗粒兼顾型品种有利于实现中稻/再生稻两季高产,并筛选出两季高产和高氮肥偏生产力品种‘旌优727’、‘旌3优177’、‘内6优103’和‘内6优107’,可在试验所在生态区中稻-再生稻种植中推广应用。     

应用SSR标记定位水稻再生力和再生产量及其构成的QTL

用两个籼稻品种明恢86和佳辐占为亲本建立的F2群体及相应的SSR分子标记连锁图,对水稻再生力和再生产量及其构成的基因进行了定位。结果定位了影响水稻再生力(再生穗数)的1个QTL,影响再生产量的1个QTL和影响产量构成的2个QTL,各QTL的加性效应均来自亲本明恢86,起增效作用。影响水稻再生穗数、结实率和单株产量的QTL位于同一染色体的相同区段上,且加性效应方向相同,这很好地解释了再生穗数与单株产量、结实率呈极显著正相关的关系。     

Heat Stress Effects are Stronger on Spikelets Than on Flag Leaves in Rice Due to Differences in Dissipation Capacity

Rice is most sensitive to heat stress at the flowering stage, with different degrees of heat damage in spikelets and leaves. To investigate the heat damage in spikelets and flag leaves, two rice genotypes, N22 (heat‐tolerant) and GT937 (heat‐sensitive), were subjected to a heat‐stress treatment (40 °C for 15 days). The results showed that more damaging was found in spikelets than in flag leaves and the heat stress significantly decreased the seed‐setting rate by 12.41 % in N22 and by 65.02 % in GT937. However, the difference in the net photosynthetic rate of the flag leaf between heat‐stressed and control was not significant. Moreover, the difference of temperatures in spikelets and flag leaves was attributed to the differences in heat dissipating. Under heat stress, the transpiration rate was significantly higher in flag leaves than in spikelets, and the temperature in flag leaves were at least 4 °C cooler than in spikelets. Although the spikelet temperatures did not differ significantly between the two genotypes under heat stress, spikelets of GT937 were more severely damaged than those of N22, which might result from the differences in the antioxidant capacities between genotypes. Results showed that little difference of superoxide dismutase, peroxidase and catalase activities of spikelets was found in N22, while significant reduction was found in GT937 under heat stress, compared with control. These results suggest that organ temperature is controlled mainly by transpirational cooling, and that heat stress is an indirect result of oxidative stress, rather than a direct result of heat damage.     

Pleiotropic effect of the dwarfing gene d18-k on cool tolerance at booting stage under the genetic background of an extremely cool-tolerant line Norin-PL8 in rice

Norin‐PL8 (‘PL8’) is an extremely cool‐tolerant line of rice in Japan that contains genes for cool tolerance originating from a javanica landrace. It was investigated to see whether the dwarfing gene d18‐k (kotaketamanishiki dwarf) exerts its pleiotropic effect on enhancing the cool tolerance at the booting stage in the genetic background of PL8. The d18‐k isogenic line of the recurrent parent PL8 (D8), PL8, and two commercial cultivars ‘Hayayuki’ and ‘Kirara 397’ were used. For each line/cultivar, the 12°C‐5‐day treatment was conducted at various times during the booting stage. In addition to spikelet fertility, the ratio (%) of the fertilized‐spikelet number of each treated panicle to the varietal mean of fertilized‐spikelet number per panicle in the control (FS‐T/C) was adopted to estimate cool temperature damage. For FS‐T/C, the lines‐cultivars ranked in the order of D8 > PL8 > ‘Hayayuki’ > ‘Kirara 397’, reflecting their cool tolerances. D8 exceeded PL8 in both pollen grain number per anther in the control and as an indicator of pollen fertility after the treatment, as a result of the effects of d18‐k. Consequently, d18‐k can be used to develop super‐highly cool‐tolerant cultivars for cool‐weather areas.