Panicle Differentiation and Spikelet Number Related to Size of Panicle in Pennisetum americanum

The size of the developing panicle of pearl millet (Pennisetumamericanum (L.) Leeke) was studied during panicle differentiation(from panicle initiation to the completion of spikelet production)in plants grown in pots or in the field and supplied with varyinglevels of nitrogen. The duration of panicle differentiationrequired a constant thermal time (day degrees) under all nitrogensupplies. However, the rate of growth of the developing panicleduring this phase was retarded by low nitrogen supply. Duringpanicle differentiation, it appeared that the developing paniclehad to reach a critical size before developmental events suchas the initiation of spikelet primordia commenced; timing ofdevelopmental events was related to the size of the developingpanicle. The number of spikelets produced depended on the rate of growthof the differentiating panicle and the duration of the phaseof spikelet initiation (from appearance of the first spikeletprimordium to completion of spikelet differentiation). Low nitrogensupply reduced the number of spikelets produced, by retardingthe rate of growth of the differentiating panicle; this delayedthe time to initiation of spikelets and thereby reduced theduration of spikelet initiation. All spikelets (irrespectiveof nitrogen supply on the mainstem and on tillers) occupiedthe same area of panicle surface at the completion of differentiationof the panicle and at anthesis. Key words: Millet, Panicle differentiation, Spikelet number     

Effect of Photoperiod and Chlormequat on Apical Development and Growth in a Spring Wheat (Triticum aestivum) Cultivar

Spring wheat, cv. Timmo, was grown under three photoperiod regimes(16, 13 and 11 h) with and without treatment with the plantgrowth regulator chlormequat (applied at the glume primordiumstage of apical development) and the relationships between apicaldevelopment, primordium initiation and growth stage examined The effects of photoperiod were generally similar to those reportedfrom other studies; shorter photoperiod slowed the rate of apicaldevelopment, increased the duration of the primordium initiationphases and reduced the rate of primordium initiation. The finalnumber of spikelets was increased, but there was no effect onnumber of floret primordia per spikelet The number of tillersproduced was also higher in the shorter photoperiods. Chlormequattreatment had a similar effect to imposing short-days: floweringwas delayed and tiller production increased There were strong correlations between certain development eventsand the phasing of primordium initiation and growth stages andthese were not affected by photoperiod or chlormequat treatments.For example, the end of spikelet primordium initiation, i.e.terminal spikelet (TS) formation, coincided with the floret-stamenprimordium stage (of the most advanced spikelet) and the endof floret primordium initiation with the stigma tic branchesand hairs on ovary wall elongating stage. Similarly, rapid stemextension growth always started at TS formation while spikeextension and spike growth commenced at TS formation and thestigmatic branches stage, respectively. Tiller production alsoceased at TS formation, when rapid stem growth started Although the timing of the phases of primordium initiation andcertain growth events were linked to apical development, therate of apical development did not determine either the rateof spikelet primordium initiation or the rates of stem and eargrowth. However, there was a strong relationship between rateof development and rate of floret primordium initiation. Therewas also a strong relationship between spike length and apicaldevelopment stage Triticum aestivum, spring wheat, photoperiod, chlormequat, apical development, primordium initiation, stem and spike growth     

Effect of Defoliation on Rate of Development and Spikelet Number per Ear in Six Wheat Varieties

The effect of leaf removal either before or at floral initiationon times from sowing to floral initiation and from floral initiationto terminal spikelet initiation, spikelet number per ear, andrate of spikelet initiation investigated in six spring wheatsunder controlled environment conditions. Defoliation delayed the times to floral and terminal spikeletinitiations significently in all varieties. However, defoliationincreased the number of spikelets per ear in the varieties 8–23,8–27 and Selkirk (up to 43 per cent in 8–27 comparedwith the control) but decreased the number in Triple Dirk, Sunsetand Kogat (up to 28 per cent in Triple Dirk). Although the rateof spikelet initiation apparently decreased in all varieties,dissection at regular intervals of Sunset and 8–23 plantsthowed that the rate dropped sharply just after defoliationin both varieties, but later the rate in 8–23 (but notin Sunset) surpassed that of the control plants. The possiblemechanism of control of spikelet number in wheat is discussed.     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

籼稻颖花分化与退化对不同播期温光的响应

试验以三系杂交籼稻‘五优308’和‘天优华占’以及常规籼稻‘黄华占’为材料,在大田条件下,设置10个播期,研究田间不同温光条件对籼稻生育期天数、颖花分化和退化数的影响.结果表明: 温度对3个籼稻品种生育期的影响比日照长度大,平均温度升高1 ℃,播种-穗分化始期天数平均减少1.5 d,而穗分化历期天数与光照和温度的关系均不密切.不同播期间每穗颖花数和颖花分化数存在显著差异.穗分化期间平均温度、最高温度和最低温度升高,有效积温增加,昼夜温差扩大,光辐射增强,有利于穗分化期干物质积累和颖花分化,各品种趋势一致.穗分化期间有效积温增加50 ℃,颖花分化数增加10.5朵,昼夜温差扩大1 ℃,颖花分化增加14.3朵,总光辐射量增加50 MJ·m^-2,颖花分化数增加17.1朵.颖花退化率与温度呈现二次项相关,极端高温或极端低温的自然条件不利于颖花形成,但低温天气对颖花退化的影响大于高温.温度低于临界温度,颖花退化率大幅增加,穗分化期临界积温为550～600 ℃,日平均温度为24.0～26.0 ℃,日最高温度为32.0～34.0 ℃,日最低温度为21.0～23.0 ℃.适宜高温、昼夜温差大、光照辐射强的自然条件利于颖花分化,并减少颖花退化.     

Polyamines and ethylene in rice young panicles in response to soil drought during panicle differentiation

This study tested the hypothesis that polyamines (PA) and ethylene (ETH) mediate the effects of soil drought on spikelet development in rice (Oryza sativa L.). Two rice cultivars, Yong You-2640 and Yang Dao-6, with vastly different panicle sizes were grown in pots under three soil moisture treatments: well-watered (WW), moderate soil drought (MD) and severe soil drought (SD), from the onset of panicle initiation to the pollen completion stage. MD treatment significantly increased spikelet differentiation, spikelet number per panicle, fully filled grain percentage and grain yield, decreasing the percentage of degenerated spikelets, sterile spikelets and partially filled grains compared to WW treatment. In contrast, SD treatment showed opposite effects. MD also increased the contents of free spermidine (Spd), free spermine (Spm) and the ratios of free putrescine, free-Spd and free-Spm to 1-aminocylopropane-1-carboxylic acid (ACC), decreasing the ETH evolution rate and ACC content in young panicles. In contrast, SD treatment showed opposite effects. Furthermore, free-Spd and free-Spm contents increased significantly, while ETH and ACC levels, and the percentage of degenerated and sterile spikelets decreased significantly under application of Spd or an inhibitor of ETH synthesis. The results were reversed when ACC or an inhibitor of Spd and Spm synthesis was applied. These findings suggest antagonistic interactions between free-PA (Spd and Spm) and ETH in response to soil drought, mediating spikelet development in rice.     

Effects of Daylength and Time of Application of Phosphorus on Growth and Grain Yield of Wheat

Three varieties of wheat. Thatcher, Falcon and Sunset. were grown under 20. 12 or 8 hour days until the initiation of spikelet primordia on the shoot apex began, and then in natural light until maturity. Phosphorus (100 mg/l P) was applied at 7, 33 or 54 days after sowing, other plants were left without phosphorus. The response of the plants to phosphorus in terms of final leaf number, grain production and number of fertile spikelets was related to time of initiation. When the time of initiation was 52 or more days after sowing there were some responses in grain yield to phosphorus, but they were independent of time of application; for initiation times of 32 days or less the earlier applications of phosphorus tended to give a greater response.     

The Effects of Daylength and Treatment with Gibberellic Acid on Spikelet Initiation and Development in Clipper Barley

The effects of photoperiod, light quality and a single applicationof gibberellic acid (GA₃) on the development of the main-stemapex in Clipper barley are reported. In 16 and 24 h days spikeletinitiation was rapid but extended over a short period whereasin 8 h photoperiods both spikelet initiation and developmentwere slower but occurred for a much longer time. Initiationalways stopped when the anther primordia were clearly visiblein the most advanced spikelet. Daylength extensions with lowintensity incandescent light were most effective when they followedrather than preceeded the 8 h period of high light intensity.Plants grown in 8 h high intensity followed by 8 h low intensitylight initiated spikelets almost as rapidly as those grown in16 h high intensity light. Thus, the effects of daylength onspikelet production were primarily mediated through photoperiodicallycontrolled processes rather than through photosynthesis andassimilate supply. The effects of applied GA₃ were long livedand greatest in short days where the rates of both spikeletinitiation and development were promoted. The parallels betweenthe effects of long days and GA₃ treatment are discussed togetherwith possible reasons for the cessation of initiation and thelong duration of the GA₃ effect. daylength, gibberellic acid, spikelet initiation, Hordeum vulgare L., barley, main-stem apex, primordia     

近地层臭氧浓度升高对杂交稻颖花形成的影响

依托全球唯一的稻田开放式空气中臭氧浓度增高系统平台,以汕优63和两优培九为供试材料,设置大气背景臭氧浓度和高臭氧浓度（比大气背景臭氧浓度高50%）两个浓度水平,研究FACE条件下高O₃浓度对杂交稻颖花形成的影响.结果表明：高O₃浓度使汕优63和两优培九每穗颖花数分别减少28朵和34朵,下降幅度分别为15%和13%.从稻穗构成看,高O₃浓度胁迫下杂交稻每穗颖花数减少主要与每穗2次枝梗颖花数明显减少有关,对每穗1次枝梗颖花数的影响较小,因此高O₃浓度胁迫下水稻每穗1次枝梗颖花数占全穗的比率增加,每穗2次枝梗颖花数占全穗的比率降低.从颖花形成看,高O₃浓度胁迫下杂交稻每穗颖花数下降主要是颖花（特别是2次颖花）的分化受到抑制所致,而颖花的退化数不增反降.上述结果表明,采取相应措施削弱高O₃浓度胁迫对颖花分化的抑制作用可能是近地层高O₃浓度条件下减少杂交稻产量损失的关键.     

Zebularine treatment is associated with deletion of FT‐B1 leading to an increase in spikelet number in bread wheat

The number of rachis nodes (spikelets) on a wheat spike is a component of grain yield that correlates with flowering time. The genetic basis regulating flowering in cereals is well understood, but there are reports that flowering time can be modified at a high frequency by selective breeding, suggesting that it may be regulated by both epigenetic and genetic mechanisms. We investigated the role of DNA methylation in regulating spikelet number and flowering time by treating a semi‐spring wheat with the demethylating agent, Zebularine. Three lines with a heritable increase in spikelet number were identified. The molecular basis for increased spikelet number was not determined in 2 lines, but the phenotype showed non‐Mendelian inheritance, suggesting that it could have an epigenetic basis. In the remaining line, the increased spikelet phenotype behaved as a Mendelian recessive trait and late flowering was associated with a deletion encompassing the floral promoter, FT‐B1. Deletion of FT‐B1 delayed the transition to reproductive growth, extended the duration of spike development, and increased spikelet number under different temperature regimes and photoperiod. Transiently disrupting DNA methylation can generate novel flowering behaviour in wheat, but these changes may not be sufficiently stable for use in breeding programs.     

Differences of Starch Granule Distribution in Grains from Different Spikelet Positions in Winter Wheat

Wheat starch development is a complex process and is markedly difference by changes in spikelet spatial position. The present study deals with endosperm starch granule distribution and spatial position during filling development. The study was conducted with pure starch isolated from wheat (Triticum aestivum L.), Jimai20 and Shannong1391, at 7–35 days after anthesis (DAA). The results showed that grain number, spikelet weight and grain weight per spikelet in different spatial position showed parabolic changes. Upper spikelets had highest starch and amylose content followed by basal spikelets, then middle spikelets. The paper also suggested the volume percents of B-type and A-type granule in grain of middle spikelets were remarkably higher and lower than those of basal and upper spikelets, respectively. However, no significant difference occurred in the number percents of the two type granule. The ratio of amylase to amylopectin was positively correlated with the volume proportion of 22.8–42.8 µm, but was negatively related to the volume proportion of <9.9 µm. The results indicated that the formation and distribution of starch granules were affected significantly by spikelet position, and grains at upper and basal spikelet had the potential of increasing grain weight through increasing the volume of B-type granules.     

Studies on the relationship between air temperature and the differentiation of young spikes of winter wheat in Beijing district

In these studies the optimum temperature indices for spikelet differentiation were found. The critical period determining the number of spikelets on a spike lies between the single ridge stage and the stage of glume differentiation. During this period a daily temperature below 7.5°C is favourable for differentiation of further spikelets. The processes of differentiation of wheat spikes need certain accumulated temperatures for a mean daily temperature above 0°C. The relationship between the rate of spikelet differentiation and temperature during the differentiation period, and the of these periods are discussed. According to the effect of climate in early spring on the number of differentiated spikelets of winter wheat, three climatic types in early spring are suggested.     

Development and Floret Survival in Wheat Ears With Supernumerary Spikelets

In the supernumerary spikelet wheat, AUS159I0, the supernumeraryspikelet primordia appeared just after the ear reached the terminalspikelet stage. Appearance of the primordia of the multiplesessile spikelets preceded that of indeterminate rachilla spikelets.Supernumerary spikelets had a lower number of potentially fertileflorets per spikelet than normal (non-supernumerary) spikeletsin the ear and thus a smaller number of grains per spikelet.Mean weight per grain in the supernumerary spikelet wheat waslower than in the cultivar, Meering, without supernumerary spikelets.Total grain number in the supernumerary spikelet ear was greaterthan in the normal ear despite the lower spikelet fertilityin the former. Within the supernumerary spikelet ear the multiplesessile spikelets had a higher number of grains per spikeletand mean weight per grain than the indeterminate rachilla spikelets.It appears possible to improve the productivity of the supernumeraryspikelet ear by breeding for reduced expression of the indeterminaterachilla spikelets. Wheat, ear development, floret survival, supernumerary spikelets, grain number     

Influence of Vernalization and Photoperiod on Supernumerary Spikelet Expression in Wheat

Two tetraploid (Triticum turgidum L.emend gr. turgidum and gr.durum) and five hexaploid wheats (Triticum x aestivum L. emendgr. aestivum) with reported tendencies for ‘branched heads’(supernurnerary spikelets) exhibited variation in its expressionunder different vernalization photoperiod and temperature regimes. Two main types of supernumerary spikelets were identified, multiplesessile spikelets (MSS) with two or more complete spikeletsat a rachis node and indeterminate rachilla spikelets (IRS)with two to 13 spikelets on an extended rachilla. The degree of supernumerary spikelet expression in wheats withvernalization response differed from those without. Short photoperiods(9–14 h) both outdoors and in a glasshouse environment,were more conducive to supernumerary spikelet expression than24 h photoperiod in both environments. The 24 h photoperiodglasshouse environment (higher mean temperatures) was leastconducive to its expression except in lines with a strong vernalizationresponse. The high stability of supernumerary spikelet expression in certaingenotypes in the different environments indicated the feasibilityof incorporating this character in breeding and selecting commercialwheats to increase grain number per head. Triticum, wheat, ear-branching, supernumerary spikelets, vernalization, photoperiod, temperature     

A genetic resource for early-morning flowering trait of wild rice Oryza officinalis to mitigate high temperature-induced spikelet sterility at anthesis

Background and Aims

High temperatures over 32–36 °C at anthesis induce spikelet sterility in rice. The use of a germplasm with an early-morning flowering (EMF) trait has been hypothesized as a way of avoiding this problem. In this study, the effect of the EMF trait on avoiding high temperature-induced sterility at anthesis by flowering at a cooler temperature in the early morning was evaluated.

Methods

The EMF trait was introgressed from wild rice (Oryza officinalis) into the rice cultivar ‘Koshihikari’ (O. sativa). First, spikelets of the EMF line and Koshihikari were subjected to rising temperatures during the daytime in the greenhouse to test for differences in spikelet sterility. Secondly, spikelets of both plants were exposed to 26, 34 and 38 °C at anthesis and to 38 °C beginning at least 1 h after flowering, in the growth chambers at 70 % relative humidity, to test for differences in tolerance to high temperatures.

Key Results

Spikelets of the EMF line started and completed flowering a few hours earlier than Koshihikari. In a greenhouse experiment, spikelets of Koshihikari opened after the air temperature reached 35 °C, but those of the EMF line could open at cooler temperatures. Under these conditions, spikelet sterility significantly increased in Koshihikari, but did not in the EMF line. The number of sterile spikelets increased as their flowering time was delayed in Koshihikari. Furthermore, the chamber experiments revealed that 60 % of the spikelets from both lines were sterile when exposed to 38 °C at anthesis, indicating that tolerance of high temperature was similar in both genotypes.

Conclusions

Reduced sterility in the EMF line subjected to rising temperatures at anthesis in the greenhouse was attributed to an earlier flowering time compared with Koshihikari. The EMF trait of wild rice is effective in mitigating anticipated yield loss due to global warming by escaping high-temperature stress at anthesis during the daytime.     

密度、施肥对旱地春小麦产量、水分利用效率和籽粒养分含量的补偿效应

为了探明旱作条件下无机营养对作物产量和水分利用效率的补偿效应,我们在宁南黄土高原半干旱地区开展了为期两年的春小麦密度与肥料试验。通过4种播种密度和5种肥力水平的综合研究结果表明,在不同处理的籽粒产量和水分利用效率排序中,播种密度为500粒／m^2时,以施肥量90kg／hm^2N和135kg／hm^2P2O5处理的产量和水分利用效率为最大。与不施肥的对照相比,增施肥料与籽粒产量和水分利用效率的提高成显著的正相关关系,相关系数分别达到0．959和0．894,而播种密度则与产量和水分利用效率的相关性不显著。增施肥料虽然能够提高可育小花数,但随着播种密度的增大,穗粒数和千粒重反而呈下降趋势,表明可育小花数对肥料水平反应敏感,而穗粒数和千粒重主要受播种密度的影响。施肥能够促进春小麦根系的生长发育,特别是促进浅层根量的增加,增强了作物的水分养分吸收。另外,不同种类肥料配施的结果表明,单施P肥或者N、P、K配合施用,可使春小麦产量分别提高44．6％和55．4％。N、P、K配合施肥还能够提高品质,使籽粒中的P、N、K含量分别提高18．5％、18．4％和8．1％。上述研究结果说明,控制播种密度、改善土壤肥力对于促进旱地春小麦高效利用有限水分具有明显的补偿效应。     

DEVELOPMENT OF THE YOUNG WHEAT SPIKE: A SEM STUDY OF CHINESE SPRING WHEAT

The number of leaves on the main culm was correlated with morphological changes in the wheat spike during development, up to the terminal spikelet stage. The developmental changes were divided into nine stages, which were compared with stages described by other investigators. Several environmental conditions were utilized to determine the consistency of morphological correlations. Although the different environments did influence the length of time required to reach the various stages, the relationship between leaf number and stage of spike development was consistent. Regardless of environmental conditions, all stages were evident. Vernalization period affected the number of spikelets. Plants vernalized 6 wk produced 17–19 spikelets, compared to 21–24 spikelets on plants vernalized 3 wk. There were three major morphological events during spike development: 1) the change from vegetative to reproductive growth, 2) lateral spikelet development, and 3) the initiation and development of the terminal spikelet.     

A Study of Floret Development in Wheat (Triticum aestivum L.)

Plants of wheat (Triticum aestlvum L.) cv. Aotea were grownat high or low nitrogen levels and in a natural photoperiodor continuous light. Starting 17–21 days from the double-ridgestage, eight plants from each treatment were sampled every 3days until anthesis, and the two basal, the sixth, and the terminalspikelets were sectioned longitudinally. A developmental scorewas assigned to each floret and rates of development calculated.Continuous light hastened development but reduced the numberof spikelets per ear, while high nitrogen delayed developmentbut increased spikelet numbers. The number of florets initiatedin each spikelet varied within narrow limits, but grain settingdepended strongly on spikelet position and on treatment. Althoughflorets were initiated in acropetal succession, the rate ofdevelopment tended to increase up to floret 4 but then declinedmarkedly. As a result grain setting was confined to basal floretpositions, although the two basal spikelets developed so slowlythat they contributed relatively little to grain yield. Distalflorets degenerated almost simultaneously at or before ear emergence,but those in intermediate positions continued to develop untilafter fertilization in the lower florets. It is argued thatthe spikelet is an integrated system in which correlative mechanismsplay a part throughout the development of the florets.     

Effect of photoperiod on development and number of spikelets of a temperate and some low-latitude wheats

Four low-latitude cultivars (two Mexican and two Rhodesian) and a Canadian cultivar were grown in controlled environments in four photo-periods, 16, 13, 10 and 7 h, respectively. Plants of two of the low-latitude cultivars were also transferred between long and short photoperiods during ear differentiation. The intervals from sowing to successive stages of ear development up to the formation of the terminal spikelet, and to ear emergence, and the number of leaves, all increased as photoperiod decreased. The Canadian cultivar responded most and one of the Rhodesian cultivars least to changes of photoperiod in these respects. However, with all the low-latitude cultivars, the interval between formation of the terminal spikelet and emergence of the ear responded similarly and relatively little to decreasing photoperiod except when photoperiod was reduced from 10 to 7 h. The mean rate of spikelet production decreased as the duration of the period of spikelet production (DSP) increased, i.e. as ear development slowed down with decrease in photoperiod. Accordingly number of spikelets per ear increased curvilinearly as DSP increased, suggesting a maximal number of spikelets of about thirty. Rate of spikelet production apparently differed between cultivars. Development of the ear slowed down when plants were moved to a shorter photoperiod and accelerated when they were moved to a longer photoperiod, both at the time at which the shoot apex began to elongate and at the double ridge stage. Final number of spikelets per ear increased when ear development was slowed down and decreased when it was accelerated.