Changes in Dry Matter, Carbohydrate and Seed Yield Resulting from Lodging in Three Temperate Grass Species

The adverse effect of lodging on grass seed yield may be attributed,in part, to assimilate limitation during the seed filling period.This investigation examined plant dry matter assimilate partitioningand seed yield as affected by lodging in three species thatare closely related but phenotypically different: tall fescue(Festuca arundinacea Schreber.), Italian ryegrass (Lolium multiflorumLam.), and perennial ryegrass (L. perenne L.). Studies wereperformed in field plots at Corvallis, Oregon, USA. Seed yieldcomponents (seed number per inflorescence, seed yield per inflorescence,and single seed mass) and leaf, stem (lower, middle, and peduncle)and seed inflorescence dry mass were measured just prior toanthesis to seed maturity. Dry mass and water soluble carbohydrates(WSC) were determined for shoot components. The reduction indry mass and WSC in leaves and stem components following anthesiswas often greater in lodged plants compared to upright plants.The relatively low seed yield depression in lodged tall fescuesuggested a higher compensation potential for partitioning reserveassimilate from leaves and stems to support seed growth anddevelopment. This potential does not appear to be present tothe same degree in Italian ryegrass and to an even lesser extentin perennial ryegrass. These findings suggest that the potentialto compensate for reduced assimilate supply during the periodof high assimilate demand by seeds may be attributed, in part,to the total assimilate reserve accumulated prior to photoassimilatereduction caused by the lodged condition. Copyright 2000 Annalsof Botany Company Tall fescue, Festuca arundinacea Schreber., Italian ryegrass, Lolium multiflorum Lam., perennial ryegrass, L. perenne L., assimilate partitioning, source–sink     

The Effect of New Tiller Growth on Carbohydrates, Nitrogen and Seed Yield per Ear in Lolium perenne L.

To clarify whether new vegetative tillers that develop aroundanthesis in aLolium perenne seed crop can depress seed yields,the possible competition for carbohydrates or nitrogen betweenthe seeds and new tillers that develop after the onset of anthesiswas investigated. In two greenhouse experiments the number oftillers per plant was varied by a combination of cutting, nitrogensupply, light quality and light intensity treatments. Two genotypeswith different tillering rates were used. Seed yield per earwas largely independent of the number of tillers and regrowthof cut tillers after the onset of anthesis. It increased inone genotype, but only under low light and a reduced nutrientavailability, and no new tillers were produced. The amount ofwater-soluble carbohydrates in the reproductive tillers increasedin both clones under these conditions. Under more favourableconditions the increased tillering rate and regrowth of tillersafter cutting did not adversely affect seed yield per ear ineither clone, although carbohydrate reserves in the floweringtillers were sharply reduced. Tiller removal increased the concentrationand amount of nitrogen in the remaining flowering tillers, irrespectiveof the amount of regrowth. It is concluded that competitionfor carbohydrates or nitrogen between the seeds and new vegetativetillers that develop after the onset of anthesis, is not a majorcause of the low and variable seed yields inL. perenne seedcrops. Processes within the ear itself are probably limiting. Lolium perenne L.; perennial ryegrass; seed yield; seed set; tillering; carbohydrates; nitrogen; competition.     

The Effect of Temperature on Seed Set and Seed Development in Detached Spikelets of Perennial Ryegrass (Lolium perenne L.)

In perennial ryegrass seed yield is low. Pollination, fertilizationand early stages of seed development are critical periods forthe realization of the yield potential. As intact plants aredifficult to handle, we used detached spikelets to study effectsof temperature and genotype on seed set and seed development. Plants of four cultivars were grown in pots. Just prior to flowering,spikelets were detached from the ears and put on water. Afterpollination, various spikelets of each plant were placed atdifferent temperatures (14/14, 17/12 or 20/15°C). Sevendays after pollination the percentage seed set and the lengthof the developing seeds (caryopses) were assessed. Only floretsin the four basal positions were used. For each cultivar an analysis of variance for unbalanced datawas carried out. There were highly significant difference amonggenotypes for seed set and caryopsis length. There was no evidencefor genotypic variation for tolerance to low temperatures. Neithertemperature nor floret position had an effect on seed set. Thecaryopsis length, however, increased with increasing temperatureand basal florets produced longer caryopses than distal florets.The detached spikelets proved to be a useful experimental tool.Copyright1993, 1999 Academic Press Lolium perenne L., perennial ryegrass, seed yield, seed set, detached spikelets culture, temperature, floret position     

The Effect of Shading During Vegetative and Reproductive Growth on the Photosynthetic Capacity of Leaves in a Grass Sward

The decline in photosynthetic capacity of successive newly expandedleaves, which occurs as a vegetative grass sward increases inleaf area, was prevented in a field sward of S24 perennial ryegrass(Lolium perenne L.) by protecting tillers from shading by theirneighbours. This adds support for the view that the declineis caused by the shading of leaves during their expansion. However, in a flowering sward where there is no such decline,the photosynthetic capacity of leaves was not reduced by shadingthem with a plastic mesh during expansion, although it was bypegging down tillers so that they developed at the bottom ofthe sward. Lolium perenne, perennial rye-grass, photosynthetic capacity, growth, shading     

Effects of shading on inflorescence size and development in temperate perennial grasses

Single plants of S24 perennial ryegrass (Lolium perenne L.) and S215 meadow fescue (Festuca pratensis Huds.) were transferred between, or exposed continuously to, contrasting light intensities obtained by decreasing the natural light in a glasshouse with Tygan shades. Inflorescence development in main shoots was studied by dissections of shoot apices, and by counts of branches and florets when ears emerged. Apical growth was slower, and spikelet initiation and inflorescence development were delayed or inhibited, in decreased light intensities. The number of main branches in the ear depended on the rate of apical growth before and after spikelet initiation, and on the time of spikelet initiation. In meadow fescue these processes were influenced by light intensity. Floret numbers per inflorescence branch were generally decreased by decreased light intensity. Most of the effects of light intensity on inflorescence development were smaller in ryegrass than in meadow fescue.     

The Volatilization of Ammonia from Perennial Ryegrass During Decomposition, Drying and Induced Senescence

The volatilization of gaseous ammonia was measured from cutherbage (leaf lamina + sheath) of perennial ryegrass (Loliumperenne L.), during a 70 d period of either decomposition ordrying, and also from intact plants of perennial ryegrass subjectedto induced senescence by shading. Volatilization during decompositionamounted to 20–47% of the herbage nitrogen, but volatilizationduring drying, and from intact plants during induced senescence,amounted to less than 1% of the herbage nitrogen. During decomposition, volatilization of ammonia was proportionallygreater from herbage containing 3.52% nitrogen than from herbagecontaining 2.32% nitrogen. Volatilization occurred more rapidlyat 20 °C than at 10 °C but, with both samples of herbageand at both temperatures, at least 4 d elapsed before appreciablevolatilization occurred. Ammonia, atmosphere, decomposition, leaves, Lolium perenne L, nitrogen, perennial ryegrass     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Photosynthesis by White Clover Leaves in Mixed Clover/Ryegrass Swards

Measurements of rates of net photosynthesis were made on singleBlanca white clover leaves on plants taken from a field-grown,mixed clover/perennial ryegrass sward during two regrowth periods. Net photosynthesis fell by 20 per cent in the first measurementperiod as leaf area index increased and the grass componentof the crop flowered, but did not change significantly in thesecond measurement period during which the grass remained vegetative. Leaves which had been artificially protected from shading inthe sward did not have significantly different photosyntheticcapacities from leaves in the undisturbed sward, even in thefirst measurement period. As leaf area index and sward height increased, successive cloverpetioles were longer, keeping the newly expanded leaves nearthe top of the sward where they received full light. It is suggestedthat it is this which allows successive clover leaves, unlikethose of vegetative grasses, to attain a high photosyntheticcapacity throughout a growth period. Trifolium repens, Lolium perenne, Photosynthetic capacity, shading, growth     

The effect of growth retardant application on floret site utilisation and assimilate distribution in ears of perennial ryegrass cv. S.24

Application of the growth retardant paclobutrazol (PP333), at 2 kg a.i. ha^-1 at spikelet initiation to plots of perennial ryegrass cv. S.24 in 1981 and 1982 significantly increased the number of seeds per spikelet present at final harvest by reducing the number of seeds aborted during seed development. Distribution of florets and seeds per spikelet was altered by PP333, as both basal and penultimate spikelets contained more florets and seeds than did those of untreated plants. Seed weight and germination were increased in florets of penultimate spikelets, although PP333 application delayed maturity by 3–5 days. In untreated plants, assimilate recovery was significantly lower from the terminal section of the ear, whereas in PP333 treated plants, no differences were found between basal, intermediate or terminal sections of the ear. PP333 increased assimilate demand at all sections of the ear when the ear and leaves were fed. The implications of this are discussed.     

Effects of Selection for Dark Respiration Rate on Enzyme Genotypes in Lolium perenne

Two lines of perennial ryegrass (Lolium perenne) that had previouslybeen selected for ‘fast’ and ‘slow’rates of leaf dark respiration were examined to determine whetherselection had differentiated allelic or genotypic frequenciesof five polymorphic enzyme loci, and determine whether respirationrates differed among genotypes. The lines were differentiatedfor genes coding for phosphoglucose isomerase (PGI) and UDP-glucosepyrophosphorylase (UDP). Respiration rates were heterogeneousamong UDP and 6-phosphogluconate dehydrogenase (6PGD) genotypes.Founder effects may have produced the genetic differentiationof lines at the PGI locus as we detected no differences amonggenotypes for respiration rates. The genetic differentiationamong lines for UDP was consistent with differences in darkrespiration among genotypes. Although we detected large differences(75%) in dark respiration rate among 6PGD genotypes in the fastrespiring line, selection did not differentiate the lines atthis locus. Lolium perenne L., perennial ryegrass, enzyme polymorphisms, dark respiration rate     

Effect of Cutting on Production and Tillering in Prairie Grass (Bromus willdenowii Kunth) Compared With Two Ryegrass (Lolium) species. 2. Reproductive Plants

Effects of time of initial cut and subsequent cutting interval(1, 2 or 4 weeks) were examined in a glasshouse during summer1988 for reproductive plants of three prairie grass cultivars(Bromus willdenowii Kunth), Westerwolds ryegrass (Lolium multiflorumLam.) and perennial ryegrass (Lolium perenne L.). Measurementswere made of tiller and leaf numbers, sites of tillering, reproductivedevelopment, and herbage quality and yields. Effect of timeof initial cutting on regrowth appeared to be independent ofstage of reproductive development and unrelated to any of themeasured plant parameters. Characteristics for each cultivaras identified during undisturbed growth prior to the initialcuts, were modified by the subsequent cutting frequencies. Perennial ryegrass had the highest yields under frequent cuttingwith high herbage quality. Westenwolds ryegrass and the prairiegrass cultivars ‘Grasslands Matua’ and ‘Primabel’had the highest yields with infrequent cutting, but lower herbagequality than in perennial ryegrass. At each cut, tiller deathin prairie grass was determined by the number of reproductivetillers, and in the ryegrasses also by the numbers of elongatedvegetative tillers. Recovery of tiller numbers was rapid andprimarily from inhibited tiller buds at the base of reproductivetillers. In prairie grass, tiller numbers were relatively unaffectedby cutting frequency, but at frequent cutting, many axillarytillers originated from vegetative tillers rather than frominhibited tiller buds at the base of reproductive tillers. Prairie grass, Bromus willdenowii Kunth, Westerwolds ryegrass, Lolium multiflorum Lam., perennial ryegrass, Lolium perenne L., first (initial) cut, cutting frequency, regrowth, leaf appearance, tillering, yield, nitrogen, water-soluble carbohydrates, herbage quality     

Tillering Responses to the Light Environment and to Defoliation in Populations of Perennial Ryegrass (Lolium perenneL.) Selected for Contrasting Leaf Length

Tillering responses to the light environment and to defoliationwere studied in two populations of perennial ryegrass (LoliumperenneL.) selected for contrasting leaf lengths. The objectiveof this study was to determine whether differences in tilleringresponses between populations, as a result of management practices,affected their competitive ability. Young seedlings were exposed,under controlled conditions, to defoliation, neutral shading(decreased photosynthetic photon flux), low red:far-red ratioand/or decreased blue light. Selection for longer leaves reducedthe tillering rate. After defoliation, this difference betweenshort- and long-leaved populations was magnified. Defoliationdecreased both site filling and phyllochron of the long-leavedpopulation but had no effect on the short-leaved population.Lowering the photosynthetic photon flux reduced the phyllochronin both population. Decreasing the red:far-red ratio reducedtillering rate by reducing site filling, whereas decreasingblue light had no significant effects on tillering. Tilleringresponses to photosynthetic photon flux and to red:far-red ratiowere similar in the two populations selected for contrastingleaf length. The implication of these tillering responses indefining the competitive ability of the grass plants is discussedin relation to their management.Copyright 1999 Annals of BotanyCompany Blue light, defoliation, far-red, irradiance, leaf size,Lolium perenne(L.), perennial ryegrass, photomorphogenesis, phyllochron, shading, site filling, tiller production.     

Neotyphodium lolii, a Fungal Leaf Endophyte, Reduces Fertility ofLolium perenneExposed to Elevated UV-B Radiation

Plants ofLolium perenne, grown with and without the balansoidfungal leaf endophyteNeotyphodium lolii, were exposed to threeultraviolet radiation treatments at an outdoor facility in theUK for 172 d. Plants were exposed to either (a) a 30% elevationabove the ambient erythemally-weighted level of UV-B (280–315nm) radiation under banks of cellulose diacetate filtered fluorescentlamps that also produce UV-A (315–400 nm) radiation (UV-B+A);(b) elevated UV-A radiation alone under banks of polyester filteredlamps; or (c) ambient levels of solar radiation under banksof unenergized lamps. The fertility of plants grown withN. loliiwassignificantly reduced by the elevated UV-B+A exposure. After172 d, these plants produced 70% fewer spikes, 75% fewer seeds,71% lower total weight of seed and 78% fewer seeds per g d.wt of plant tissue than plants colonized byN. loliiwhich wereexposed to ambient radiation. There was no discernible effectof elevated UV-B+A exposure on the fertility of endophyte-freeplants. Plants irradiated with UV-B+A developed 14% thickerleaves than those exposed to ambient radiation. Those whichwere irradiated with elevated UV-A alone produced seeds thatwere 20% heavier than plants exposed to ambient levels of radiation.Plants grown withN. loliihad 7% thicker leaves, 4% thicker stembases and 7% fewer tillers than those grown without it. Thefresh mass of tillers of plants grown withN. loliiwas 11% greaterthan those of endophyte-free plants, owing to their higher moisturecontents. These results suggest that the fertility ofL. perennecolonizedbyN. loliiin the natural environment could be deleteriouslyaffected by elevated fluxes of UV-B radiation associated withstratospheric ozone depletion and that this may affect the populationdynamics of the species.Copyright 1998 Annals of Botany Company Fungal leaf endophyte,Neotyphodium lolii, perennial ryegrass (Lolium perenne), stratospheric ozone depletion, UV-B radiation.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

Effect of Cutting on Production and Tillering in Prairie Grass (Bromus willdenowii Kunth) Compared With Two Ryegrass (Loliunt) Species. 1. Vegetative Plants

Effects of cutting to 3 or 6 cm stubble height at frequenciesof 1, 2 or 4 weeks were investigated in young, vegetative, spacedplants of prairie grass (Bromus willdenowii Kunth), a tetraploidWesterwolds ryegrass (Lolium multiflorum Lam.) and perennialryegrass (Lolium perenne L.). Plants were grown for 8 weekson nutrient solution in a growth cabinet at day/night temperaturesof 15/10°C and in a short photoperiod. Leaf appearance,site filling and tiller numbers were all reduced by both increasedcutting frequency and a lower cutting height. The extent ofthese reductions was least in prairie grass and greatest inWesterwolds ryegrass. Relative growth rates in all species respondedin a similar manner with more frequent cutting and a lower cuttingheight. Cutting frequency had the greatest effect on growthrates, although the effect of cutting height increased withtime. Results confirm general recommendations of long intervalsbetween defoliations to achieve high yields for vegetative prairiegrass, but the relative amounts of dry matter harvested underthe different cutting regimes may be no different to that obtainedin ryegrass. Stubble height was of lesser importance in determiningyields. A typical U-shaped curve for depletion and recovery in water-solublecarbohydrates occurred after defoliation in all species, butlevels remained low at frequent cutting. Water-soluble carbohydratelevels in stubble and roots were higher in prairie grass. Regrowthat the end of the experiment was highly correlated with totalstubble and root weights (r = 0.84), while regrowth per tillershowed a good correlation with water-soluble carbohydrate content,although the response varied between species. Prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., cutting frequency, cutting height, leaf appearance, tillering, site filling, yield, regrowth, nitrogen, water-soluble carbohydrates     

Effect of Flowering on the Photosynthetic Capacity of Ryegrass Leaves Grown With and Without Natural Shading

The photosynthetic capacity of newly expanded leaves of vernalizedor non-vernalized plants of S24 perennial ryegrass (Lolium perenneL.), grown in long or short photoperiods, was measured in twoexperiments. In the first, leaves were protected from shadingduring development, while in the second, the natural shade ofneighbouring tillers in a sward was allowed. In the first experiment there was little effect of vernalization,day length or flowering, and leaves in all treatments had photosyntheticrates at 250 W m^–2 of between 28 and 32 mg CO₂ dm^–2h_–1.In the second experiment the photosynthetic rate of successiveleaves fell as sward leaf area increased. This downward trendwas reversed, however, in flowering tillers in the vernalizedlong-day treatment, while in the other treatments, which didnot flower, photosynthetic capacity continued to fall. It isconcluded that the leaves of reproductive tillers have highphotosynthetic capacities because stem extension carries themto the top of the canopy where they are well illuminated duringexpansion. Lolium perenneL, ryegrass, photosynthetic capacity, flowering, shading, vernalization     

Effect of Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 1. Carbon and Nitrogen Economies of Mixed Swards at Low Temperature

Simulated mixed swards of perennial ryegrass (Lolium perenneL. cv. S23) and white clover (Trifolium repens L. cv. S100)were grown from seed under a constant 10°C day/8°C nighttemperature regime and their growth, and carbon and nitrogeneconomies examined. The swards received a nutrient solution,every second day, which contained either high (220 µgg^–1) or low (40 µg g^–1) nitrate N. The High-N swards had rates of canopy photosynthesis and drymatter production (over the linear phase of growth) similarto those previously shown by mixed swards at high temperature.The Low-N swards grew more slowly; canopy photosynthesis, ata given LAI, was similar to that at High-N but lower LAI's weresustained. Clover increased its contribution to total carbonuptake and total dry weight throughout the period in the Low-Ntreatment and, despite the fact that grass took up most of theavailable nitrate, clover maintained a consistently higher Ncontent by virtue of N₂-fixation. At High-N, grass dominated throughout the measurement period.Earlier, when plants grew as spaced individuals, clover grewless well than grass, but once the canopy was closed it hada similar relative growth rate and thus maintained a steadyproportion of total sward dry weight. It is proposed that earlyin the development of the crop, leaf area production is thelimiting factor for growth, and that in this respect cloveris adversely affected by low temperature relative to grass.Later, as the LAI of the crop builds up, and the canopy becomesfully light intercepting, net canopy photosynthesis plays amore dominant role and here the higher photosynthetic rate perunit leaf area of the clover is crucial. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, low temperature, nitrogen, photosynthesis     

Water Use Characteristics of Dactylis glomerata L., Lolium perenne L. and L. multiflorum Lam. Plants

Cocksfoot (Dactylis glomerata L.). perennial ryegrass (Loliumperenne L.) and Italian ryegrass (L. multiflorum Lam.) plantswere grown on deep (75–95 cm) columns of soil in glasshousesand growth rooms with and without irrigation. The species inwhich growth declined least rapidly after water had been withheldwere those which transpired most slowly. During early establishmentin the glasshouse cocksfoot transpired least because of slowroot growth. In the growth room, when root systems were deeperand denser, perennial ryegrass transpired least because of lowleaf water conductance. Results are discussed in relation to(a) drought resistance in the three species; (b) breeding forincreased drought resistance through modifying root distributionand leaf water conductance; and (c) the use of isolated soilcolumns in water relations studies. Dactylis glomerata L., Lolium perenne L., Lolium multiflorum Lam., cocksfoot, perennial ryegrass, Italian ryegrass, transpiration, roots, leaf water conductance     

Control of pH in a System of Flowing Solution Culture using a Microcomputer

A system is described which uses a microcomputer to controlpH in flowing solution culture and a brief account is givenof its performance when intact perennial ryegrass (Lolium perenneL.) plants were grown in nutrient solutions with pH controlledat 5.0, 5.5, 6.0 and 7.0. Key words: pH, Microcomputer     

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