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     

Temperature Response of Vernalization in Wheat: Modelling the Effect on the Final Number of Mainstem Leaves

This paper outlines a modelling approach which predicts theeffect of both continuous and intermittent low temperature regimeson the final number of leaves in winter wheat. The model takesaccount of the balance between the concurrent processes of leafprimordium initiation and rate of saturation of vernalization,and their response to temperature. The inverse of the time tosaturation of vernalization, at which stage final leaf numberis set, is modelled as a linear function of vernalizing temperature,between 0 and 17 °C. The rate of leaf primordium initiationis modelled using the established linear relationship betweenrate and temperature above 0 °C. Final leaf number is hencethe product of the number of leaf primordia initiated once vernalizationis saturated. In the model, genotypes are characterized by (1)the slope and intercept of the linear response of the rate ofsaturation of vernalization to temperature in the vernalizingrange, and (2) by a development rate towards floral transitionat on-vernalizing temperatures (above 17 °C). The modelis tested against data from experiments where six cultivarsof winter wheat plants of different ages were exposed to a rangeof low temperature regimes, including continuous and intermittentvernalizing temperatures. Overall, the model predicted, withr ²values of 70–90%, the final leaf number across a rangeof six to 21 leaves. Prediction of final leaf number for somecultivars was better in continuous than in intermittent vernalizingregimes. This modelling approach can explain the often-conflictingreports of the effectiveness of different temperatures for vernalization,and the interaction of plant age and vernalization effectiveness. Triticum aestivum L.; wheat; vernalization; rate; temperature; leaf number; modelling; phenology; flowering     

The Nature and Duration of Gene Action for Vernalization Response in Wheat

Four near-isogenic lines of wheat were studied to determinethe nature and duration of gene action for vernalization responseunder 2 weekly vernalization periods from 0 to 10 weeks. With time to floral initiation the Vrn 1 Vrn 2 and Vrn 1 vrn2 genotypes showed a cumulative response whereby days to floralinitiation decreased as the period of vernalization increased.The vrn 1 Vrn 2 and the vrn 1 vrn 2 genotypes also showed acumulative response for periods of vernalization less than 6weeks for the former and 8 weeks for the latter. Days to earemergence was closely related to days to floral initiation dueto the constancy of the period from floral initiation to earemergence across all lines and treatments and, consequently,they gave similar measures of the relative strength of vernalizationresponse. It appears that genes for vernalization response ceaseto act after floral initiation. The implications of these findings to breeding for increasedadaptability and yield in wheat are discussed. Triticum aestivum, wheat isogenic lines, vernalization, floral initiation, ear emergence, gene action     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

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 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     

Environmental Control of Flowering in Barley (Hordeum vulgare). III. Analysis of Potential Vernalization Responses, and Methods of Screening Germplasm for Sensitivity to Photoperiod and Temperature

Three genotypes of barley were subjected to 18 potentially vernalizingpre-treatments, comprising constant temperatures of 1, 5 or9 °C in factorial combination with photoperiods of 8 or16 h d^–1 for 10, 30 or 60 d^–1. These pre-treatedseeds or seedlings, together with non-pre-treated seeds as controls,were then transferred to each of four growing-on regimes, namelyday/night temperatures of 18/5 °C or 24/3 °C in factorialcombination with photoperiods of 11 or 16 h d^–1. The timesfrom sowing to awn emergence were recorded. The warmer growing-onregime (mean 19 °C) was not supra-optimal in long days,but in short days it considerably delayed awn emergence in allthree genotypes. In cv. Athenais there was no specific responseto the potentially vernalizing pre-trcatments: the rate of progresstowards awn emergence could be treated as a linear functionof the integrated responses to temperature and photoperiod actingindependently throughout development. In addition to these responses,cv. Gerbel B and the land-race Arabi Abiad also responded tolow-temperature vernalization and the response became saturatedduring the longer-duration pre-treatments. In Arabi Abiad, therate at which vernalization occurred, and the period requiredto saturate the response, were not greatly influenced by differencein pre-treatment temperature between 1 and 9 °C. In contrast,in Gerbel B the cooler the temperature of pre-treatment thegreater the saturated response to vernalization, the greaterthe effect of each day of pre-treatment, and the shorter theperiod required to saturate the response. Models of the photothennaland vernalization responses were combined in a single entitywhich described the influence of environment on rate of development.Simple germplasm-screening techniques are proposed for genotypecharacterization so that the phenotypic flowering response canbe estimated for any environment Hordeum vulgare L., barley, flowering, phtoperiodism, vernalization, photothennal time, germplasm screening     

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     

Developmental Regulation of Low-temperature Tolerance in Winter Wheat

Vernalization and photoperiod genes have wide-ranging effectson the timing of gene expression in plants. The objectives ofthis study were to (1) determine if expression of low-temperature(LT) tolerance genes is developmentally regulated and (2) establishthe interrelationships among the developmental stages and LTtolerance gene expression. LT response curves were determinedfor three photoperiod-sensitive LT tolerant winter wheat (Triticumaestivum L. em Thell) genotypes acclimated at 4 °C under8 h short-day (SD) and 20 h long-day (LD) photoperiods from0 to 112 d. Also, three de-acclimation and re-acclimation cycleswere used that bridged the vegetative/reproductive transitionpoint for each LD and SD photoperiod treatment. A vernalizationperiod of 49 d at 4 °C was sufficient for all genotypesto reach vernalization saturation as measured by minimum finalleaf number (FLN) and confirmed by examination of shoot apicesdissected from crowns that had been de-acclimated at 20 °CLD. Before the vegetative/reproductive transition, both theLD- and SD-treated plants were able to re-acclimate to similarLT₅₀(temperature at which 50% of the plants are killed by LTstress) levels following de-acclimation at 20 °C. De-acclimationof LD plants after vernalization saturation resulted in rapidprogression to the reproductive phase and limited ability tore-acclimate. The comparative development of the SD (non-flowering-inductivephotoperiod) de-acclimated plants was greatly delayed relativeto LD plants, and this delay in development was reflected inthe ability of SD plants to re-acclimate to a lower temperature.These observations confirm the hypothesis that the point oftransition to the reproductive stage is pivotal in the expressionof LT tolerance genes, and the level and duration of LT acclimationare related to the stage of phenological development as regulatedby vernalization and photoperiod requirements. Copyright 2001Annals of Botany Company Triticum aestivum L., wheat, low-temperature tolerance, vernalization, photoperiod, phenological development     

Effects of the Reversal of Day and Night Temperatures on Tillering and on the Elongation of Stems and Leaf Blades of Wheat

Different cultivars of wheat (Triticum aestivum L.) were grownin cabinets, under a 12 h photoperiod, at constant temperatures,and high day/low night and low day/high night temperatures.Plants were also transferred at different ages, between 18/10°C and 10/18 °C regimes. Application of the growth regulatorsCCC and TIBA was tested at 18/10 °C and GA₃ and IAA at 10/18°C. The reversal of day and night temperatures did not affect spikedifferentiation or the numbers of leaves and elongating internodes.However, tillering and tiller development were markedly promotedby the low day/high night temperature regimes whereas the elongationof leaf blades and stem internodes were suppressed under theseregimes. These effects were attributed to the effects of thetemperature regimes on the endogenous hormone balance of theplants. Considering the results of the transfer and growth regulatortreatments it was concluded that there were no obligatory associationsamong the number of tillers appearing, their subsequent development,leaf blade length, and stem elongation. It is suggested thatthe study of the physiological mechanisms controlling thesecharacters may benefit from experimentation under reciprocallydiffering day night temperature regimes.     

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     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Effect of Vernalization and Red Light Illumination of Seedlings of Bread Wheat (Triticum aestivum L.) on the Temperature Profile of cAMP Phosphodiesterase Activity

Phenotypic manifestations of Vrn(vernalization) and Ppd (photoperiod) genes responsible for transition of bread wheat Triticum aestivumL. to generative growth (flowering) are mutually related. Since the mechanism of phytochrome-induced photoperiodism involves the enzymes of cyclic adenosine monophosphate metabolism, and phosphodiesterase in particular, we tested involvement of phosphodiesterase in the process of winter wheat vernalization and formation of flowering competence in alternate wheat requiring a long photoperiod but no vernalization for its transition to flowering. We studied temperature dependence of phosphodiesterase activity in vernalized and unvernalized winter wheat on the one hand and in etiolated and red light illuminated seedlings of alternate wheat on the other hand. Short-term experiments demonstrated that red light illumination is similar to long photoperiod by the effect on the long-day plants. Both influences induced a pronounced inversion of the temperature profile of phosphodiesterase activity in the 28–45°C range. We propose that phosphodiesterase is involved in vernalization and can serve as a receptor of low temperature in winter wheat. Changed temperature profile is a radical control mechanism of phosphodiesterase activity in response to the influences (red light and vernalizing temperatures) responsible for competence of various bread wheat forms for generative growth.     

The Effects of Temperature and Light Intensity on Embryo Numbers in Wheat Doubled Haploid Production through WheatxMaize Crosses

Triticum aestivumxZea mayscrosses are now widely used in theproduction of wheat doubled haploids to produce homozygous lines.Seasonal effects are known to influence the number of haploidembryos produced through wheatxmaize crosses, but the effectsof temperature and light have not been quantified. This studyinvestigated the effect of temperature and light intensity onhaploid embryo production. New Zealand wheat cultivars weregrown in a glasshouse until booting when they were transferredto growth cabinets at three temperatures (day/night; 17/12,22/17 or 27/22 °C at an irradiance of 250 µmol m^-2s^-1PAR).In another experiment, wheat lines were transferred to a growthcabinet at one of three light intensities (300, 500 or 1000µmol m^-2s^-1PAR at 22/17 °C day/night, with a photoperiodof 16 h). The temperature and light intensity at which pollinationswere made and subsequent fertilisation and embryo developmentoccurred, significantly (P<0.01) influenced the frequencyof haploid embryo production. The optimal temperature for embryorecovery was 22/17 °C. The greatest number of embryos wasproduced at a light intensity of 1000 µmol m^-2s^-1. Thesefindings will result in improvements in the overall efficiencyof the wheatxmaize system for wheat doubled haploid production.Copyright1998 Annals of Botany Company Intergeneric crossing, temperature, light intensity,Triticum aestivum,wheat,Zea mays,maize.     

Reanalysis of Vernalization Data of Wheat and Carrot

Vernalization is an important determinant of the growth, development,and yield of biennial and perennial crops. Accurate simulationof its response to temperature is thus an important componentof successful crop systems modelling. Vernalization has a lowoptimum temperature compared to other temperature responsesof plants, and thus may be difficult to treat using expressionsthat are appropriate for other plant processes. This paper examinesthe application of a simple equation that has been used forother processes. It reads as v=V_max(T_max-T_{Tmax- Topt} ) (T_Topt)^{T_optTmax-T_opt}, where v is thedaily rate of vernalization progress at temperature T, T_optandT_maxare the optimum and maximum temperatures for vernalization,respectively, andV_max is the maximum daily rate of vernalization(the inverse of the minimum number of days required to completevernalization), which occurs at T_opt. The model was appliedto published vernalization data for wheat and carrot. The fitsto data were good (adjusted R²for wheat of 0.94, for carrot0.98), with estimatedT_opt and T_maxbeing 5.7±0.5 and 21.3±1.4°C, respectively, for wheat ‘Norin 27’ and 6.6±0.2and 14.1±0.3 °C for carrot ‘ Chantenay RedCored’. The estimated parameters, in particular the highT_maxfor wheat, were close to those reported using differentanalytical approaches. It was suggested that the function wouldbe useful for summarizing vernalization data, and that its usewould avoid the abrupt changes that are inevitable when differentlinear relationships are used for part of the overall response.It was also suggested the high T_maxshould be taken into accountwhen interpreting data obtained with wheat grown under warmconditions. Copyright 1999 Annals of Botany Company Plant, vernalization, temperature response, modelling, wheat (Triticum aestivum L.), carrot (Daucus carota L.).     

The Effect of High Temperature at Different Stages of Ripening on Grain Set, Grain Weight and Grain Dimensions in the Semi-dwarf Wheat 'Banks'

Grain number in the wheat cultivar Banks was reduced by up to11 % with a rise in temperature from 21/16 °C to 30/25 °Cover a 10-d period immediately following first anthesis in general,the upper ‘d’ and ‘c’ florets were moreaffected by high temperature than the basal ‘a’and ‘b’ florets within a spikelet and florets fromthe upper spikelets were more sensitive than those lower onthe ear Grain weight and grain length at maturity were most affectedby a 10 d period of high temperature commencing 7–10 dafter anthesis However, if dry-matter accumulation between thestart of a treatment and grain maturity was used as a base forcomparison, the response was more uniform throughout development,with a peak in sensitivity 25 d after anthesis Although grainposition within an ear did not have a large effect on the responseto temperature, grains from the basal spikelets were more sensitivethan those from the apex, and the upper floret grains of a spikeletwere more sensitive to high temperature than those at the base There is a need to obtain, for a range of cultivars, more comprehensivedata on the effect of the timing and degree of temperature stressfollowing anthesis, for use in interpreting the response torising temperatures late in the development of the crop in thefield Triticum aestivum L, wheat, temperature, grain development     

Developmental Base Temperature in Different Phenological Phases of Wheat (Triticum aestivum)

The linear relationship between temperature and developmentrate has been widely recognized and it has been suggested thatthermal units (the summation of daily mean temperature abovea base temperature) can predict the phenological developmentof a crop. The aim of this paper was to determine the base temperaturefor different phenological phases of wheat. Two mediterraneanwheat cultivars and five sowing dates were used to obtain differentmean temperatures during development and different developmentalrates. The linear regression of development rate against meantemperatures for each period indicated that there were no uniquebase temperatures for all stages of the life span and valuesclose to 4°C and to 9·5°C were found to be bestfits for base temperatures before and after the terminal spikeletstage of both cultivars. A model to predict wheat developmentwas validated with another data set, which included differentwheat cultivars and sowing dates. Estimates of the error indevelopmental prediction by using a single base temperatureof 0°C is discussed as a function of separate developmentstages. Key words: Wheat development, base temperature, thermal time, Triticum aestivum     

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     

Effects of Temperature, Photoperiod and Seed Vernalization on Flowering in Faba Bean Vicia faba

Factorial combinations of three photoperiods (10, 13 and 16h), two day temperatures (18 and 28 °C) and two night temperatures(5 and 13 °C) were imposed on nodulated plants of six diversegenotypes of faba bean (Vicia faba L.). Plants were grown inpots in growth cabinets from both vernalized (1.5±0.5°C for 30 d) and non-vernalized seeds. The times from sowingto the appearance of first open flowers (f) were recorded. Seedvernalization decreased the subsequent time taken to flowerin almost all genotype x growing environment combinations (theexceptions were plants of the cv. Maris Bead grown in threecooler, short-day regimes). The influence of temperature andphotoperiod on the rate of flowering was quantified, using amodel applied previously to other long-day species of grainlegume in which positive linear relations between both temperatureand photoperiod and the rate of progress towards flowering areassumed to apply. A significant positive linear response ofrate of progress towards flowering to limited ranges of meandiurnal temperature was detected in all six genotypes, but inthree genotypes (Syrian Local Large, Aquadulce and Maris Bead)the 28 °C day temperature reduced the rate of progress towardsflowering - suggesting that the optimum temperature for floweringin these genotypes is below 28 °C. In four genotypes (MarisBead, Giza-4, Aquadulce and BPL 1722) a significant positiveresponse to photoperiod, typical of quantitative long-day plants,was observed only in plants grown from vernalized seeds. Incontrast, plants of the genotype Zeidab Local grown from bothnon-vernalized and vernalized seeds showed the same positiveresponse to photoperiod, whereas plants of the land-race SyrianLocal Large were consistently unresponsive to photoperiod. Theimplications of this range of responses amongst diverse genotypesare discussed in relation to screening germplasm. Vicia faba, faba bean, flowering, photoperiod, temperature, seed vernalization, germplasm screening     

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