The Effects of Floret Sterilization on Grain Number and Grain Weight in Wheat Ears

This paper describes the effects of sterilizing certain floretson the development of others within the ears of wheat, cultivarMaris Ranger. Sterilization of all the florets in spikelets2, 4, 6, and 8 (numbered from the base of the ear upwards) ledto more grain setting and greater grain growth in the untreatedspikelets. These compensatory increases were insufficient toprevent a depression in the yield of grain per ear. Sterilizationof more than one of the basal florets of spikelet 8 led to amore frequent setting of the grain in the distal florets onthat spikelet and to the centrally positioned grain becomingheavier. The physiological basis for the inhibitory influences of theolder and developing grain on the unfertilized florets and youngergrain is discussed.     

Reproductive Development in Lolium temulentum L.: Spike Morphogenesis and Grain Set Limitations

Reproductive development in cereals is not easy to investigatebecause their quantitative response to environmental factorsmakes it difficult to synchronize the plants. In this paper,one of our aims was to assess whether Lolium temulentum strainCeres, a qualitative long-day grass, could serve as a modelof reproductive development for cereals. The morphological patternsfrom floral transition to seed set were studied. A flowering scale was established to evaluate developmentalrate during spike morphogenesis. Apex growth was found to increaseaccording to biphasic kinetics; double ridge appearance markedthe beginning of an exponential phase. Developmental progression and apical growth rate were both increasedby giving repeated long days. In contrast, the final numberof lateral spikelets (20–25) could not be manipulatedafter the beginning of long-day treatment. When plants were kept in continuous light from the beginningof induction, double ridges appeared on the fifth 24 h cycle.Spikelet initiation began in the upper mid-part of the spike,and then extended acro- and basipetally. The phase of spikeletinitiation lasted 6 d, with l?5 to 1?9 spikelets being produceddaily. Within each spikelet, florets were initiated at an averagerate of l?3 primordia per day and developed acropetally. Thefirst signs of apical site degeneration were observed in themost developed upper spikelets just before heading. Ear emergenceoccurred between the 20th and 25th cycles of continuous light;anthesis was observed 6 or 7 d later. The proportion of floretssetting grain averaged about 40%. Grains were produced mainlyin the lower spikelets while the upper mid-part of the inflorescenceshowed a much lower fertility rate. Complex developmental gradients described in this paper suggestthat L. temulentum could serve as a model of reproductive developmentin cereals, with the added advantage of flowering in responseto a single long-day. Key words: Lolium temulentum L., spike morphogenesis, spikelet number, floret number, grain set     

Effects of Removing Floral Organs, Light Penetration and Physical Constraint on the Development of Wheat Grains

The effects on grain weight of removing spikelet and floralorgans, other manipulations of the florets or spikelets andcovering intact or treated spikes to reduce the amount of lightwere tested. Removal of organs which exposed the developing grain to increasedlight intensity resulted in a reduction in grain size. The restrictionin grain growth was already apparent 2 weeks after anthesisand was accompanied by a more compact pericarp. Covering thetreated spikes with opaque bags resulted in normal pericarpstructure and restoration of grain weight. Only a small portionof the restoration effect could be attributed to the increaseof humidity under the covers. Treatments which exerted physical constraint on the developinggrain reduced its size and affected its shape. The size of thefloret cavity and the transmission of light through floral bractsare shown to be two of the factors controlling grain growth. Triticum destivum L., Triticum spelta L., wheat, morphogenesis, histogenesis, grain development, glume, lemma, palea     

Exploring abiotic stress on asynchronous protein metabolism in single kernels of wheat studied by NMR spectroscopy and chemometrics

Extreme climate events are being recognized as important factorsin the effects on crop growth and yield. Increased climaticvariability leads to more frequent extreme conditions whichmay result in crops being exposed to more than one extreme eventwithin a growing season. The aim of this study was to examinethe implications of different drought treatments on the proteinfractions in grains of winter wheat using ¹H nuclear magneticresonance spectroscopy followed by chemometric analysis. Triticumaestivum L. cv. Vinjett was studied in a semi-field experimentand subjected to drought episodes either at terminal spikelet,during grain-filling or at both stages. Principal componenttrajectories of the total protein content and the protein fractionsof flour as well as the ¹H NMR spectra of single wheat kernels,wheat flour, and wheat methanol extracts were analysed to elucidatethe metabolic development during grain-filling. The resultsfrom both the ¹H NMR spectra of methanol extracts and the ¹HHR-MAS NMR of single kernels showed that a single drought eventduring the generative stage had as strong an influence on proteinmetabolism as two consecutive events of drought. By contrast,a drought event at the vegetative growth stage had little effecton the parameters investigated. For the first time, ¹H HR-MASNMR spectra of grains taken during grain-filling were analysedby an advanced multiway model. In addition to the results fromthe chemical protein analysis and the ¹H HR-MAS NMR spectraof single kernels indicating that protein metabolism is influencedby multiple drought events, the ¹H NMR spectra of the methanolextracts of flour from mature grains revealed that the amountof fumaric acid is particularly sensitive to water deficits. Key words: Chemometrics, drought, fumaric acid, grain-filling, HR-MAS NMR, PARAFAC, PCA trajectory, single kernel, wheat Received 19 August 2008; Revised 14 October 2008 Accepted 24 October 2008     

The Influence of Genes for Vernalization Response on Development and Growth in Wheat

Studies were made of the influence of genes for vernalizationresponse on the growth and development of four near-isogeniclines of bread wheat (Triticum aestivum L.). The duration from sowing of flower initiation, terminal spikeletformation and ear emergence all increased with increasing vernalizationresponse. There was a close positive relationship between thedays from sowing to flower initiation and from sowing to earemergence, indicating that the duration of either phase of developmentis a useful measure of relative vernalization when daylengthdoes not limit the rate of development. Total spikelet number per ear and the duration of spikelet initationincreased with increasing vernalization response and there wasa correspondingly higher rate of spikelet initiation in thetwo lines with stronger vernalization response. Most of the differences in growth between the lines were associatedwith diferences in development caused by the vrn genes. Maximumtotal above-ground dry matter and total leaf area per plantincreased with increasing vernalization repsonse but relativegrowth rate and leaf area per plant were not significantly differentbetween the lines. There were no differences in net assimilationrate between the four lines until 40 d from sowing; thereafterit decreased, with the greatest decrease in the line with thestrongest vernalization response. Flower initiation, terminal spikelet formation, spikelet initiation, ear emergence, growth rate     

Studies on the Physiology of Flowering of Timothy (Phleum pratense L.) II. Influence of Daylength and Temperature on Size of the inflorescence

Inflorescence length in timothy increases when the photoperiodis reduced from 24 to 14 hours of light; it is also increasedby a reduction in ambient temperature from 75° to 55°F. There is a linear relation between total floret number andear length. Both factors affect ear length by influencing therate of growth of the spike between spikelet initiation andear emergence; this implies an effect on either the number ofprimary spikelet initials or the number of florets producedby branching, or both. Experiments with Lolium temulentum, wheredaylength and temperature influenced initiation and ear developmentin a way similar to that observed in timothy, suggest that thesefactors affect the number of florets at each primary initial.The interrelations of internal and external factors and theirinfluence on inflorescence size in the grasses is discussed.     

Phenotypic and genetic analysis of spike and kernel characteristics in wheat reveals long-term genetic trends of grain yield components

Key message

Phenotypic and genetic analysis of six spike and kernel characteristics in wheat revealed geographic patterns as well as long-term trends arising from breeding progress, particularly in regard to spikelet fertility, i.e. the number of kernels per spikelet, a grain yield component that appears to underlie the increase in the number of kernels per spike.

Abstract

Wheat is a staple crop of global relevance that faces continuous demands for improved grain yield. In this study, we evaluated a panel of 407 winter wheat cultivars for six characteristics of spike and kernel development. All traits showed a large genotypic variation and had high heritabilities. We observed geographic patterns for some traits in addition to long-term trends showing a continuous increase in the number of kernels per spike. This breeding progress is likely due to the increase in spikelet fertility, i.e. the number of kernels per spikelet. While the number of kernels per spike and spikelet fertility were significantly positively correlated, both traits showed a significant negative correlation with thousand-kernel weight. Genome-wide association mapping identified only small- and moderate-effect QTL and an effect of the phenology loci Rht-D1 and Ppd-D1 on some of the traits. The allele frequencies of some QTL matched the observed geographic patterns. The quantitative inheritance of all traits with contributions of additional small-effect QTL was substantiated by genomic prediction. Taken together, our results suggest that some of the examined traits were already the basis of grain yield progress in wheat in the past decades. A more targeted exploitation of the available variation, potentially coupled with genomic approaches, may assist wheat breeding in continuing to increase yield levels globally.

     

A Comparison of the Development of Multiflorous and Standard Wheats

This study was conducted to compare patterns of phenologicaldevelopment and agronomic traits of multiflorous and standardwheats (Triticum aestivum L. em. Thell.) when grown in environment-controlledgrowth rooms (20/15 °C, 16/8 h, day/night, 600 µmolm ² S ¹). Six winter and six spring habit genotypes were studiedin separate experiments. The winter multiflorous genotypes wereearlier than the winter standard genotypes. Their earlinessresulted in lower total biomass and grain yields, lower leafand tiller numbers per primary culm, and spikelet numbers perspike. Within the spring group, few differences were associatedwith spike type although the multiflorous genotypes had reducedgrowth as indicated by lower tiller and spike numbers per plant.Leaf emergence in the multiflorous genotypes, as in the standardgenotypes, was found to be a linear function of time. The tilleringpatterns of the multiflorous types were less pronounced thanfor the standards with lower maximum tiller numbers, and restricteddie-back and reinitiation. Floret numbers per spikelet werehigher in the multiflorous types due to higher initiation rates,longer initiation periods and/or reduced periods of die-back.The multiflorous trait was negatively associated with spikenumber and greater numbers of florets per spikelet did not alwaystranslate into greater numbers of kernels per spikelet. Becauseyield compensation was incomplete, yields per plant were lowerin the multiflorous genotypes than the standards. Triticum aestivum L. em, Thell., wheat, multiflorous trait, yield components, development     

The Effect of Population Density on Floret Initiation, Development and Abortion in Winter Wheat

There is little information in the literature concerning thephysiological basis of the relationship between plant populationdensity and kernel number in winter wheat (Triticum aestivumL.). Thus, two experiments were conducted to evaluate this relationship.Expt 1, involving three population densities, was carried outnear Taian, China in 1982 and in Expt 2, two densities wereevaluated near Lexington, Kentucky in 1986. Plants were sampled every 2 d in the spring, main stem spikeswere dissected and florets were scored according to a 10-stagescale of development. The rate of primordia initiation increasedas density increased until the point at which primordia numberswere equal in all treatments. After this point, an increasein density reduced the primordia initiation rate. In both experimentsincreasing density reduced the total number of floret primordiainitiated and the number of kernels per spike. In Expt 1 theeffect of density on kernel number per spike was accounted forapproximately equally by the effect of density on number ofprimordia initiated and floret abortion. In Expt 2, however,floret abortion was influenced much less by density and accountedfor only 7 % of the variation in kernel number per spike. Thekey result was that the effect of density was determined earlyin floral development. The data suggest that yield losses athigh densities may be determined too early in development tobe offset by N applications at the terminal spikelet stage. Triticum aestivum L., spike development, spikelet development, seeding rate     

疏剪不同穗位小穗对小麦籽粒结实和粒重的影响

１９９７～１９９８年在河南省农作物品种展览中心以中大穗小麦品种温麦６号为材料,设计了去除不同穗位小穗的试验。结果表明,去除不同位小穗对结实粒数和粒重的影响不同, 除顶端小穗的粒数下降较多,穗粒重最低,却除基部小重申对结实粒数和粒重的影响较小,穗粒数和粒重下降较少;却除中部小穗对结实粒数影响较大,穗粒数量小,其穗粒重因剩余籽粒单粒重增加而得以一定程度补偿。     

Effects of the Photoperiod Genes Ppd1 and Ppd2 on Growth and Development of the Shoot Apex in Wheat

Two major genes influencing the photoperiod response in wheat,Ppd1 and Ppd2, have been identified on the group 2 chromosomes.Substitution lines, which had been characterized on the basisof time of ear emergence as carrying either the insensitiveor sensitive alleles of the two Ppd genes, were used to investigatethe effect of these genes on development. They were grown undershort photoperiods, and growth and development of the shootapex was measured. The primary influence of the Ppd genes was on ear growth. Inthe plants carrying the insensitive alleles, Ppd1 and Ppd2,the relative growth rate of the floral apex was faster thanthat of plants with the sensitive alleles, ppd1 and ppd2. Therewere no differences in the rate of spikelet initiation, butthe spikelets of the ppd lines grew and developed more slowly. The Ppd2 material segregated for another gene located on chromosome2B affecting duration of the life cycle. This gene also affectedthe relative growth rate of the ear. It was considered that the major effect of the Ppd1, Ppd2 andthe second genetic factor on chromosome 2B is on floral growthrate. Differences in apex morphology, stem growth and ear emergenceare thought to be due to the differences in floral apex growthand size. Wheat, photoperiod genes, shoot apex development, shoot apex growth     

Combinatorial control of meristem identity in maize inflorescences

The architecture of maize inflorescences, the male tassel and the female ear, is defined by a series of reiterative branching events. The inflorescence meristem initiates spikelet pair meristems. These in turn initiate spikelet meristems which finally produce the floret meristems. After initiating one meristem, the spikelet pair and spikelet meristem convert into spikelet and floret meristems, respectively. The phenotype of reversed germ orientation1 (rgo1) mutants is the production of an increased number of floret meristems by each spikelet meristem. The visible phenotypes include increased numbers of flowers in tassel and ear spikelets, disrupted rowing in the ear, fused kernels, and kernels with embryos facing the base of the ear, the opposite orientation observed in wild-type ears. rgo1 behaves as single recessive mutant. indeterminate spikelet1 (ids1) is an unlinked recessive mutant that has a similar phenotype to rgo1. Plants heterozygous for both rgo1 and ids1 exhibit nonallelic noncomplementation; these mutants fail to complement each other. Plants homozygous for both mutations have more severe phenotypes than either of the single mutants; the progression of meristem identities is retarded and sometimes even reversed. In addition, in rgo1; ids1 double mutants extra branching is observed in spikelet pair meristems, a meristem that is not affected by mutants of either gene individually. These data suggest a model for control of meristem identity and determinacy in which the progress through meristem identities is mediated by a dosage-sensitive pathway. This pathway is combinatorially controlled by at least two genes that have overlapping functions.     

Seed Weight inLolium perenneas Affected by Interactions among Seeds within the Inflorescence

Little is known about interactions between seeds within theinflorescence of perennial ryegrass (Lolium perenneL.) and theireffect on final seed weight. These relations were investigatedin two glasshouse experiments using two genotypes, by reducingthe number of seeds in an inflorescence at anthesis. In thefirst experiment, entire spikelets were removed to study therelations between seeds in different spikelets. The effectson seed dry weight were not proportional to the number of spikeletsremoved. In one genotype, removal of two-thirds of the spikeletsincreased seed dry weight of the remaining seeds by 15%. Inthe other genotype, such treatment did not increase seed dryweight. In the second experiment, investigating seed interactionswithin a spikelet, either two proximal seeds or two centralseeds were maintained in a spikelet by removing the other ovulesin combination with no or 75% shading. Shading by 75% reducedseed dry weight by about 10%. In the unshaded treatment, seeddry weight was not affected by ovule removal. Under shading,the central seeds in a spikelet were about 12% heavier if theygrew alone, in contrast to the proximal seeds. The effects ofa reduction in seed number on seed dry weight were not relatedto the final nitrogen concentration of seeds. These experimentsshow that assimilate partitioning and the relationship betweenseeds in the inflorescence of perennial ryegrass are alreadylargely determined at anthesis; increasing seed yield by manipulationsafter anthesis is not feasible.Copyright 1998 Annals of BotanyCompany. Lolium perenne, perennial ryegrass, seed growth, seed interactions, shading, spikelet removal.     

Interrelationship between Meristematic Regions of Developing Inflorescences of Four Cereal Species

A cultivar from each of four cereal species (Avena sativa L.,cv. Swan, Hordeum vulgare, L., cv. Clipper, Triticum aestivumL., cv. Gabo, and Secale cereale L., cv. South Australian Rye)was grown in controlled environment chambers in a 10-h photoperiod(short days) or 10-h photoperiod supplemented with a 6-h extensionby incandescent light. The developmental morphology of the inflorescenceswas followed to ascertain whether there were any common developmentalinterrelationships between the species. Inflorescence internodeelongation was initiated when the floret initial first appeared,irrespective of whether it occurred on the most advanced lateralspikelet or on the terminal spikelet of the rachis. The glumes(infertile bracts) of the terminal spikelet of the rachis wereinitiated when the first second-order inflorescence branch appeared,irrespective of whether the second-order inflorescence branchwas a floret initial or a lateral spikelet, as in Triticum sp.,or an inflorescence (panicle) branch, as in Avena sp. Cessationof the activity of the apical meristem, as measured by primordiumformation, was not correlated with any particular stage of floraldevelopment but appeared to be due to a lack of nutrients causedby an increasing competitiveness for the available nutrientsfrom the developing spikelets which are situated closer to thevascular system than the apical meristem.     

Expression of Vernalization Requirement and Spikelet Number in Synthetic Hexaploid Wheats and their Triticum tauschii and Tetraploid Wheat Parents

Vernalization requirement, as measured by days from sowing toear emergence (plants grown under an 18-h photoperiod), andspikelet number per ear were recorded for 17 synthetic hexaploidwheats and the six tetraploid (Triticum durum) and the ninediploid T. tauschii parents used to synthesize them. The tetraploid parents and the synthetic hexaploids had springphenotypes (little or no vernalization requirement) whereasthe T. tauschii parents were all winter types (strong vernalizationrequirement). The tetraploid wheats and the synthetic hexaploidsreached ear emergence 50·3 to 63·8 d and 58·2to 75·3 d after sowing, respectively, while the T. tauschiilines reached ear emergence 114·3 to 179·5 d aftersowing. The spring habit of the synthetic hexaploids demonstrates theepistasis of spring over winter habit. It is considered thatwith a presumed single vrn locus in the diploid species T. tauschiithe range of ear emergence in these lines is consistent withthe action of multiple alleles at that locus. Although there was no general epistasis for spikelet number,the tetraploid parents appear to be exerting more influenceover spikelet number in the synthetic hexaploids than T. tauschii.The well established association between the duration from sowingto ear emergence and spikelet number was not evident eitherwithin each ploidy group or when the 32 lines were consideredtogether. Triticum tauschii, Triticum durum, hexaploid wheat, spikelet number, vernalization requirement     

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     

Pre-flowering Growth and Development of the Inflorescences of Maize: I. PRIMORDIA PRODUCTION AND APICAL DOME VOLUME

The growth and development of the main stem and the two uppermostaxillary apices of maize were studied during the period fromemergence until flowering. Plants were grown in the field undervarying levels of applied nitrogen fertilizer at two times ofsowing. The effects of daylength were isolated from those oftemperature by making comparisons of growth and developmenton a thermal time basis. The growth and development of the terminal (male) apex and thetwo uppermost axillary (female) apices followed the same patterns,with apex volumes increasing curvilinearly with increase innumber of leaf or husk primordia. The RGR(relative growth rateof volume) of the terminal apex was, however, only approximatelyone-tenth of the axillary apices. There was no difference ingrowth and development between the first and second axillaryapices before flowering: other factors, such as accumulationof dry weight, rather than primordia production, must be responsiblefor an axillary apex's potential to bear grain. Applied N, andto a lesser extent short days, increased the rates of growthand development of all the apices. For example, applied N increasedthe RGR (volume) of the apical domes, and the rate of productionof spikelet primordia, by about 25%. All axillary apices and treatments showed a single relationshipbetween number of spikelets and surface area of the ear: a favourableenvironment (e.g. high N) simply accelerated the progressionof spikelet production and area expansion along this singlepath. We conclude that this path is probably determined geneticallyand that N and time of sowing influence potential yield of maizethrough effects on the surface area of the ear but not on thedensity of spikelets formed. Key words: Maize, inflorescence, N application, daylength, temperature, apex volume     

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.     

Growth and light absorption of some planktonic cyanobacteria, diatoms and Chlorophyceae under simulated natural light fluctuations

Specific growth rates of Limnozhrix redekei, Planktothrix agardhii(cyanobacteria), Synedraacus, Stephanodiscus minutulus (diatoms),Scenedesmus acuminatus and Scenedesmus armatus (Chlorophyceae)were compared under different time structures of illumination,but the same daily light exposure, at 20C. Fluctuating irradiancesimulating a uniform rapid transport of the algal cells acrossthe aquatic light field on a cloudless day with Z^eu/Z^mix=1 wascompared with constant irradiance throughout the same photoperiodof 12 h length as well as a photoperiod of 6 h length. Fluctuatinglight (30 min for a cycle) resulted in a decrease in specificgrowth rates as compared with constant irradiance at the samephotoperiod length. This decrease amounts to 15–20% fordiatoms, 20–25% for Chlorophyceae and 35–40% forcyanobacteria, respectively. The decrease is somewhat lowerif the fluctuations simulating mixing are slower (60 min fora cycle). The specific growth rate is also decreased by a shorterphotoperiod, but this effect is more species specific. Regardingthe in vivo absorption spectra, fluctuating light or a shorterphotoperiod has little or no effect on the Chlorophyceae anddiatoms studied, whereas cyanobacteria show an increase in lightabsorption by chlorophyll a and phycobilins.     

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