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     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

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     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

Duration and Rate of Development Phases in Wheat in Two Environments

Six cultivars of bread wheat (Triticum aestivum ssp. vulgareL. amend. Thell.) of diverse climatic origin and different developmentalpatterns were studied under two environments, (a growth roomand an outdoors sowing) for the duration and rate of completionof their developmental phases. The need for vernalization in the cultivar Cappelle Desprezsubstantially increased the length of the vegetative phase,particularly in the growth room. Large differences in the durationof reproductive initiation and stem elongation phases betweenCappelle Desprez and the other cultivars in the growth roomsowing suggests an influence of veralization beyond the vegetativephase. Differences between the two environments influenced the durationof all phases of development, giving pronounced between-cultivarvariation in both the stem elongation and ripening phases. Rates of reproductive initiation and stem elongation for thecultivars, within and between the two environments appearedto be largely independent. The rate of spikelet initiation wassignificantly decreased in the growth room compared with theoutdoor sowing. The duration of the phases of development withineach cultivar appeared to be independent of each other, indicatingthe possibility for adjusting the rate, or duration, of a phaseof development comparatively free of a compensatory change inthe rate, or duration, of other phases. Triticum aestivum ssp, vulgare, wheat, vegetative phase, flower initiation, vernalization, photoperiodism     

Relationships Between Grain Weight and the Size of Floret Cavity in the Wheat Spike

The volume of the floret cavity at different floret positionsalong the spike and within a single spikelet was estimated in10 Triticum aestivum and three T. durum lines by injecting floretcavities with liquid silicone rubber which solidified thereafter.Highly significant correlation coefficients, ranging from 0.40to 0.76 were found between floret volume and grain weight; inmost lines the basal florets had a higher correlation than theterminal ones. The relationships between floret volume and grainweight were characterized by an intercept of about 30–60per cent of the mean grain weight (heavy-grained lines havinga larger intercept) and a slope of about 1 mg µI^–1.Differences in grain size and shape, both within spike as wellas among lines, closely reflected the variation in the sizeof floret cavity. The data support the hypothesis that grainweight is partly determined by the volume of the floret cavity. Grain weight, grain volume, floret cavity     

Morphological Analysis of Leaf and Tiller Number Dynamics of Wheat (Triticum aestivumL.): Responses to Temperature and Light Intensity

In recent literature on Gramineae species, leaf and tiller numberdynamics have been studied by analysing site filling and thephyllochron of the mainstem. However, site filling is influencedby three components: (1) the phyllochron of the mainstem anddaughter tillers; (2) specific site usage (i.e. fraction ofbuds that ultimately develop into a visible tiller at a specificsite); and (3) HS-delay (i.e. difference in Haun Stage (HS)between the parent tiller and daughter tiller above the pointwhere the daughter tiller appears). These three morphologicalcomponents affecting site filling were studied under differentenvironmental conditions in a growth chamber experiment withspring and winter wheat (Triticum aestivumL.). Treatments weretemperature (daily average 10.5, 15.5 or 20.5 °C) and lightintensity (111, 191 or 286 µmol m^-2s^-1). Effects of temperatureand light intensity on phyllochron were well described by equationsalready reported in the literature. Specific site usage washigher at cooler temperatures and greater light intensitiesand was related to tiller position. It is proposed that theseeffects on specific site usage reflect differences in availabilityof local assimilate for tiller appearance. HS-delay of a tillerwas shorter if the expected tiller appearance was later andwas only slightly affected by light intensity or temperature.This new concept, combining HS-delay and specific site usage,can be useful in constructing more general models of the effectsof environmental factors on the dynamics of leaf number andleaf area ofGramineaespecies.Copyright 1998 Annals of BotanyCompany Triticum aestivum; wheat; phyllochron; temperature; light intensity; leaf number; tillering; site filling; site usage.     

Respiration and Dry Matter Accumulation Around the Time of Anthesis in Field Stands of Winter Wheat (Triticum aestivum)

Rates of CO₂ efflux from the aerial parts of eight winter wheat(Triticum aestivum L. em Thell) genotypes were determined duringspike emergence, anthesis and early grain filling over two seasons.Dry weight data were also recorded at flag leaf full expansionand anthesis Respiration rates on a ground area basis did not differ (P >0–05) among the times of day when measurements were made.In contrast, highly significant day-to-day effects (P > 0–001)were evident. Daily respiratory efflux was consistently highduring spike emergence, declining to lower values before andafter anthesis in each year. Changes in daily respiration wereanalysed in terms of a two-parameter respiration model. Modelpredictions suggested that changes in chemical composition ofthe dry matter formed during ontogeny could explain the day-to-dayeffect Although no genotypic differences in respiration (ground areabasis) and crop growth rate were found, significant negativecorrelations between crop d. wt and respiration rate per unitd. wt were evident. Genotypic differences in crop d. wt alsobecame more distinct from the first harvest to the second. Theseobservations are discussed in terms of genotypic variation inmaintenance respiration Wheat, respiration, genotype, ontogeny     

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     

Expression of Vernalization Genes in Near-lsogenic Wheat Lines: Duration of Vernalization Period

Vernalization periods ranging from 0 to 11 weeks at 4 °Cwere used to study the reproductive development of four near-isogeniclines of wheat (Triticum aestivum L. em. Thell). From the resultsfor days to anthesis two types of gene action were identified,a threshold (all-or-nothing) response (vrn3 and/or vrn4) anda cumulative (graded) response (vrn1). The action of anothergene (vrn2) intensified these two responses. Based on the actionof genes, a model relating days to anthesis to genotype wasderived. Final leaf number and days to anthesis were shown tobe closely related after adjusting for differences due to theduration of vernalization treatment. No relationship betweendays to anthesis and spikelet number was observed. This studyemphasises the need to understand vernalization at the levelof the gene in terms of responses and interactions. Such knowledgeshould enable the plant breeder to predict and more preciselycontrol reproductive development. Triticum aestivum L., wheat, vernalization, gene action, isogenic lines     

Cellular Levels of Ribulose 1,5 Bisphosphate Carboxylase and Chloroplast Compartment Size in Wheat Mesophyll Cells

Pyke, K. A. and Leech, R. M. 1987. Cellular levels of ribulose1,5 bisphosphate carboxylase and chloroplast compartment sizein wheat mesophyll cells.—J. exp. Bot. 38: 1949–1956. The amount of the photosynthetic enzyme ribulose 1,5 bisphosphatecarboxylase (RUBISCO),as determined in mesophyll cells in primarywheat leaves was related to the size of the chloroplast compartmentwithin the cell for wheat species of three ploidy levels. Asimilar comparison was made for several genotypes of the hexaploidbreadwheat Triticum aestivum. Estimation of total chloroplastvolume per mesophyll cell was made assuming chloroplasts tobe oblate spheroid in shape. A significant correlation was found between the amount of RUBISCOper cell and the total chloroplast volume per cell for diploid,tetraploid and hexaploid wheat species. A significant correlationbetween cellular RUBISCO level and total chloroplast volumeper cell was also observed for a range of genotypes of the hexaploidT. aestivum but these genotypes of T. aestivutn accumulate agreater amount of RUBISCO per unit chloroplast volume than doany other wheat species. For these genotypes of T. aestivumthe stromal concentration of RUBISCO was estimated at 0·5mol m^–3 with a ribulose Msphosphate binding site concentrationof 4·0 mol m^–3. These results are discussed with respect to a gene dosage hypothesisto explain the accumulation of RUBISCO in leaf mesophyll cells. Key words: Ribulose, bisphosphate carboxylase, wheat chloroplasts, mesophyll cells     

Insights on the role of tillering in salt tolerance of spring wheat from detillering

Tillering is reduced by salinity, with the primary and secondary tillers being more affected than is the mainstem. To understand the importance of tillering in the salt tolerance of wheat plants, two contrasting genotypes of spring wheat (Triticum aestivum L.) were grown in a greenhouse under saline or non-saline conditions and were subjected to five progressive levels of detillering. Regardless of the genotype and salinity, shoot dry weight, seed yield and seed number per plant were all significantly decreased in the treatments where only one or two tillers per plant remained compared with the untouched treatment (more than three tillers), whereas these same variables per tiller tended to be increased on a per tiller (mainstem or substem tiller) basis. The increased seed yield per tiller observed with tiller reduction may be attributed to the enhanced seed number within the spikelet. Under saline conditions, the reductions in shoot dry weight, seed yield and seed number per plant for the salt-tolerant genotype Kharchia were of a greater magnitude in the treatments where only one or two tillers per plant were present compared with the untouched treatment, whereas the magnitude of this reduction in the salt-sensitive genotype Sakha 61 was decreased.     

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     

Transport of Recently Assimilated15N Nitrogen to Individual Spikelets in Spring Wheat Grown in Culture Solution

Two cultivars of spring wheat ( Triticum aestivum L.), Sport(high protein) and WL4 (low protein), were grown to maturityin culture solution. Nitrogen in the form of nitrate was addedin daily doses at stepwise-decreasing relative rates to ensurenormal development, and both cultivars received the same totalamount of N during development. At weekly intervals from anthesisto maturity the daily nitrate dose was, for selected groupsof plants, labelled with¹⁵N. After the labelling period theselected plants were harvested and analysed. The cultivar WL4produced more biomass than Sport, as well as more spikeletsand more grains per ear, with a higher mean grain weight, suchthat grain yield of WL4 was 57% greater than Sport. The earsof both cultivars were heterogenous: mean grain weight was highestin middle spikelets, which also contained more grains; the Ncontent followed the pattern of dry weight with more N in themiddle spikelets; but the N concentration was practically thesame in all spikelets (2.15% of d. wt in WL4 and 3.33% in Sport).The distribution of¹⁵N showed that the main stem ear maturedmuch earlier than tiller ears. The results of this nitrogen-labellingexperiment show that, late in development, substantial amountsof recently-absorbed N were immediately assimilated and transportedto the ears. Transport of¹⁵N decreased earlier to the top spikeletsthan to the bottom spikelets. As both cultivars were grown underidentical conditions and both received the same amount of Nit was concluded that the difference in grain N concentrationwas not caused by differences in the capacity of N assimilationand translocation but rather by different rates of accumulationof non-nitrogenous dry matter in the grains. Ear; grain; nitrate; nitrogen transport; Triticum aestivum L.; yield     

Responses of Leaf and Tiller Emergence and Primordium Initiation in Wheat and Barley to Interchanged Photoperiod

The influence of constant (9, 13 and 19 h) and reciprocally-interchangedphotoperiods [at terminal spikelet (TS) or triple mound (TM)]on leaf, tiller and primordium development were examined usingphotoperiod-responsive cultivars of spring wheat, ‘UQ189’ and spring barley, ‘Arapiles’. In bothspecies, constant longer photoperiod reduced the duration fromsowing (S) to double ridge (DR), as expected. However, photoperiodsensitivity was not restricted to this mainly vegetative phase.There was also a marked increase or reduction in the durationof reproductive phases between TS/TM and heading (H) when plantswere transferred to shorter or longer photoperiods respectively,compared with controls. These responses were largely independentof the photoperiod during previous phases although minor effectsof the previous photoperiod were observed. For both species,the time course of leaf emergence was linear, or bi-linear,depending on the final leaf number on the main stem. The rateof leaf emergence was faster for the first six to eight leavesthan for the leaves appearing subsequently. The rate of emergenceof early-formed leaves was independent of photoperiod whereasthe rate of emergence of later leaves varied with photoperiod.Photoperiod also affected the dynamics of tillering. The rateof leaf primordium initiation was little affected by variationin photoperiod, but the rate of spikelet initiation increasedwith increases in photoperiod. The rates of leaf and spikeletprimordium initiation were both substantially higher in barleythan in wheat. The fact that the reproductive phase from TS/TMto H was largely independent of the duration of the previousphase provides evidence that this phase might be geneticallymanipulated to increase the time for floret development andhence grain number. Copyright 2000 Annals of Botany Company Photoperiod, rate of development and leaf emergence, tillering, wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.)     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling     

Development in wheat as affected by timing and length of exposure to long photoperiod

Seeds of a spring wheat (Triticum aestivum L. cv. ‘Condor’)were vernalized and then grown at 19C in two naturally–litenvironments, one with a moderate (12 h) and the other withlong (18 h) photoperiod. Treatments consisted of transfers ofplants from the moderate to the long photoperiod chamber ondifferent occasions, or for periods of different durations.The main objectives were to determine whether wheat developmentresponds to current and previous photoperiodic environmentsand whether there is a juvenile phase when the plants are insensitiveto photoperiod. Plants under constant 18 h photoperiod had fewerleaves which appeared faster than those under constant 12 hphotoperiod (i.e. phyllochron was increased from 4.4 to 5.1d leaf^–1). Plants transferred from 12 h to 18 h photoperiodat terminal spikelet appearance (TSA) reached anthesis 4 d earlierthan plants retained at 12 h, while plants under continuouslong photoperiod (18 h) completed this phase most rapidly. Thus,there was some evidence for a historic effect of photoperiodon development. Exposure to long photoperiod during the first 5 d after plantemergence accelerated the rate of development towards anthesis,suggesting that there was no juvenile period of photoperiodicinsensitivity. There were, however, changes during ontogenyin the degree of sensitivity to long photoperiod, increasingfrom seedling emergence to a maximum c. 15 d later, and thendecreasing again. Although all treatments were imposed beforeTSA, the response was not limited to the pre-TSA phase, suggestingthat well before the terminal spikelet appeared, the plant wasalready committed to the initiation of this spikelet. Spikeletnumber decreased with delayed transfer to long photoperiod witha minimum for plants transferred to long days from 16-20 d afterseedling emergence. Additionally, there was a trend for an increasein the rate of leaf appearance (decrease in phyllochron) whenthe plants were exposed to long days between 10 and 35 d afterseedling emergence. Although the differences were small, whenconsidered in conjunction with the effects on final leaf numberthey become important in explaining differences in time to anthesis. Key words: Development, flowering, leaf number, photoperiod, phyllochron, Triticum aestivum     

Growth of Near-isogenic Wheat Lines Differing in Development--Plants in a Simulated Canopy

An understanding of the principal factors regulating the growthof temperate cereals will identify opportunities to manipulatecrop growth. In an accompanying paper (Gomez-Macpherson, Richardsand Masle,Annals of Botany82: 315–322, 1998), growth aroundthe start of floral initiation was studied in isogenic wheat(Triticum aestivumL.) lines grown as spaced plants. In thispaper, two of the same near-isogenic wheat lines were grownas mini-canopies in a growth chamber. The objective was to determinewhether results obtained using spaced plants also apply to plantsgrown in a simulated canopy as a first step to emulate fieldconditions. Biomass of plant organs, leaf area and leaf andtiller appearance were determined from sowing to ear emergenceof the early developing line. Contrary to results obtained usingspaced plants, lines differed in their above-ground biomassaccumulation, although total plant biomass accumulation wassimilar. After the early line reached terminal spikelet stage(TS), biomass partitioning to the roots and leaves decreased,whereas partitioning to the stem and ear increased. This resultedin a lower root:shoot ratio in the early flowering line thanin the late line which remained vegetative. Tiller senescencealso began after TS in the early line whereas no tiller senescencewas observed in the late line during the experiment. Furthermore,after TS, net assimilation rate was greater and leaf area ratiowas lower in the early line. It is suggested that, after reachingTS, plants grown in a canopy become source limited comparedto widely spaced plants, or compared to plants that have notreached TS, and this results in less root growth.Copyright 1998Annals of Botany Company Development, growth, partitioning,Triticum aestivumL., wheat.     

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