Variation in Selection for. Leaf Water Conductance in Relation to Growth and Stomatal Dimensions in Lolium perenne L.

A simple, rapid technique for direct selection for leaf waterconductance (LWC) in two populations of Lolium perenne L. isdescribed. Measurements were made with a diffusion porometerin growth rooms on the youngest fully expanded leaf of eachtiller. Considerable variation in LWC was found between 100genotypes of each population. Most of the variation in totalLWC was attributed to variation in adaxial LWC and it was shownthat ignoring abaxial LWC gave very similar ranking of genotypesto those using total LWC. Selection criteria were then establishedwhich maximised the repeatability of LWC measurements and allowedselection of groups of plants significantly different from oneanother in LWC. The variation in LWC was not related eitherto stomatal length or number, or to growth rate. Lolium perenne L., perennial ryegrass, abaxial and adaxial, leaf water conductance, selection, diurnal rhythms, ontogenetic changes, growth, stomatal dimensions     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 2. Grown as Young Plants from Seed

Young plants of two selection lines of Lolium perenne cv. S23with ‘fast’ and ‘slow’ rates of ‘maturetissue’ respiration were individually grown from seed,together with plants of S23, their common parent, in 9.2 cmpots in a controlled environment at 20/15 °C day/night temperatures. No significant differences were found between the genotypesin leaf extension and tiller production during this early stageof their growth. They did differ however, by an average of 26%,in the rate of dark respiration of fully expanded leaf laminae.The use of a simple model demonstrated that such a differencein respiration could alone account for the different rates ofdry matter production shown by the selection lines when grownas young crops from seed. Possible penalties of ‘slow’respiration are also considered. Lolium perenne L., ryegrass, respiration, maintenance respiration, stimulated swards, leaf growth, tiller production, carbon economy     

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     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 1. Response of Leaf Extension to Temperature during the Transition from Vegetative to Reproductive Growth

The potential for leaf extension of plants of Lolium perennecv S24 growing in small artificial communities under naturalconditions was measured as the plants progressed from the vegetativeto the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’were sown in autumn and overwintered in an open, unheated glasshouseIndividual swards from the batch sown in 1975 were brought into a growth room on two occasions in spring 1976 to measuretheir potential for leaf extension at a range of temperatures(5–20 °C) Individual swards from the batch sown inautumn 1976 were brought in to the growth room on 15 occasionsbetween November 1976 and May 1977 and their potential for leafextension was measured at a single temperature of 15 °CFrequent dissections were made in both years to describe changesin the developing apex. The potential for leaf extension at 15 °C decreased fromc 17 mm day^–1 in November to c 10 mm day^–1 in mid-winter.In January, the potential rapidly increased threefold to reach30mm day^–1 by mid February The increase began coincidentwith the earliest stages of floral initiation and was completedby the time of double-ridge formation Spring-grown vegetativeplants, however, showed potential rates of < 20 mm day^–1at 15 °C The results are discussed in relation to reproductive developmentand to changes in the carbohydrate strategy of the plants inearly spring Lolium perenne L perennial ryegrass, leaf extension, temperature response     

The Effect of Air Humidity on Photosynthesis of Ryegrass and White Clover at Three Temperatures

Increasing leaf-air vapour pressure deficit (VPD) decreasedthe stomatal conductance and the photosynthetic rate of leavesof ryegrass (Lolium perenne L.) and white clover (Trifolhimrepens L.) at light saturation and at lower irradiance. In ryegrassboth conductance and photosynthesis, and in clover photosynthesis,decreased less with increasing VPD in low irradiance than theydid at an irradiance which saturated photosynthesis. In ryegrass,relative to their values at 10 mb, photosynthesis and conductancedecreased less with increasing VPD at 25 °C than at 20 or16·5 °C. In white clover, relative conductance (butnot photosynthesis) was less reduced at 25 than at 16·5°C Measurements of VPD of air in the leaf canopy of a field-growncrop are combined with the observed responses of photosynthesisto VPD and temperature in a model. This shows that high VPDis likely to depress photosynthesis significantly and that,during a typical day, the rate of light saturated photosynthesismay remain fairly steady, because the depression of photosynthesisdue to rising VPD is offset by the stimulation due to risingtemperature Perennial ryegrass, Lolium perenne L., White clover, Trifolhim repens L., photosynthesis, leaf conductance, water vapour pressure deficit, temperature     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

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     

Selection for Nitrogen Responses in Lolium

Lolium populations from a diallel cross were tested for heritabilityof response to nitrogen in sand culture, in pots of soil andfinally in the field. Heritability of response was found insand culture for several growth parameters including leaf areaand shoot dry weight. Response in pots of soil varied significantlybetween populations, but in a small experiment heritabilitywas not shown to be significant. Selection of individual genotypes within the diallel populationswas then carried out simultaneously for nitrate uptake fromsolutions and for growth in pots. The selected plants were finallytested for nitrogen response in simulated swards in the field.L. perenne plants did not differ after selection for high orlow uptake, but L. multiflorum and interspecific hybrids producedlines which showed significant differences in nitrogen response. A second cycle of selection confirmed the lack of variationin the L. perenne lines chosen, and revealed a complex situationin L. multiflorum whereby the effects of selection were apparentlyreversed. In the L. perenne x L. multiflorum hybrid lines, however,the large differences between high and low response selectionswere maintained. High response plants had broad pale leaveswhile low response plants had rather narrow dark leaves.     

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     

Increased Defoliation Frequency Depletes Remobilization of Nitrogen for Leaf Growth in Grasses

Plants ofLolium perenneandFestuca rubrawere grown in sand culturereceiving all nutrients as a complete nutrient solution containing1.5 mMNH₄NO₃, and subjected to one of three defoliation treatments:undefoliated, defoliated on one occasion, or defoliated weekly.¹⁵Nlabelling was used to determine the rate of N uptake, allowingthe amount of N remobilized from storage for the growth of thetwo youngest leaves (subsequently referred to as ‘newleaves’) growing over a 14 d period after defoliationto be calculated. The total plant N uptake by both species wasreduced, compared with undefoliated plants, by both a singleand repeated defoliation, although neither caused complete inhibitionof uptake. Regularly defoliatedL. perennehad a greater reductionin root mass, concomitant with a greater increase in N uptakeper g root than did regularly defoliatedF. rubra. In both species,the amount of N derived from uptake recovered in the new leaveswas unaffected by the frequency of defoliation. BothL. perenneandF.rubramobilized nitrogen to the new leaves after a single defoliation,mobilization being sufficient to supply 50 and 41%, respectively,of the total nitrogen requirement. In regularly defoliated plants,no significant nitrogen was mobilized to the new leaves inL.perenne, and only a small amount was mobilized inF. rubra. Plantsachieved greater leaf regrowth when only defoliated once. Weconclude that increasing the frequency of defoliation of bothL.perenneandF. rubrahad little effect on the uptake of nitrogenby roots which was subsequently supplied to new leaves, butdepleted their capacity for nitrogen remobilization, resultingin a reduction in the rate of growth of new leaves. Lolium perenne; Festuca rubra; defoliation frequency; mobilization; root uptake; nitrogen     

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     

A Comparison of the Growth of the C4 Grass Spartina anglica with the C3 Grass Lolium perenne at Different Temperatures

Dunn, R., Thomas, S. M., Keys, A. J. and Long, S. P. 1987. Acomparison of the growth of the C₄ grass Spartina anglica withthe C₃ grass Lolium perenne at different temperatures.—J.exp. Bot. 38: 433–441. S. anglica is one of the few C₄ species which occurs naturallyin cool temperate zones. It is known to attain photosyntheticrates which equal or exceed those of C₃ grasses over the temperaturerange typical of the spring and summer in cool temperate climates.This study examines whether S. anglica can also attain comparablegrowth rates at these temperatures. Seedlings of S. anglicaand L. perenne cv. S23 were grown in controlled environmentsat 10,15,20 and 25 °C. Quantitative growth analysis wasconducted by taking frequent harvests to determine the progressionsof leaf area and plant weight of individual plants with time.Quadratic regressions were found to describe these progressionswell. Instantaneous derived growth parameters were calculatedfrom the fitted regressions. Both absolute and relative growthrates of S. anglica were significantly lower than for L. perenne,this being largely attributable to a lower ratio of leaf areaproduction per unit of plant dry weight. Although the amountof dry matter invested into leaves was similar, the leaf areaper unit of leaf dry weight was lower in S. anglica. In comparisonto L. perenne, the rate of dry matter accumulation per unitof leaf area (ULR) was higher in S. anglica at 25 °C andinitially equal at 10 °C. Prolonged exposure to 10 °Csteadily reduced ULR in S. anglica which approached zero at80 d. Although growth in S. anglica is reduced more by low temperaturethan it is in L. perenne, by comparison to other C₄ speciesthe assimilatory capacity of S. anglica is more tolerant oflow temperature exposure. Key words: C4 photosynthesis, temperature, quantitative growth analysis     

The Effect of Wind on Grasses: V. LEAF EXTENSION DIFFUSIVE CONDUCTANCE PHOTOSYNTHESIS IN THE WIND TUNNEL

Festuca arundicacea and Lolium perenne were grown in a controlled-environmentwind tunnel at high (7.4 m s^–1) or low (1.0 m s^–1)windspeed. The rate of leaf extension was markedly reduced atthe high windspeed. This effect could not be attributed to waterstress, for, although the leaf conductance increased with exposureto high wind, no effect on leaf water potential was detected.Nor was the rate of photosynthesis affected when the windspeedwas changed. Moreover, concentrations of ethylene in the windtunnel were too low to explain the observations. It is suggestedthat mechanical stimulus itself may have caused the reductionin leaf growth rate.     

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     

Leaf and Tiller Production of Prairie Grass (Bromus willdenowii Kunth) and Two Ryegrass (Lolium) Species

A detailed morphological study of three prairie grass cultivars(Bromus willdenowii Kunth) was conducted under ‘vegetative’and ‘reproductive’ growth conditions (short andlong photoperiods) and at different temperatures. Perennialryegrass (Lolium perenne L.) and Westerwolds ryegrass (Loliummuhiflorum Lam.) were compared during vegetative growth. Prairie grass had higher leaf appearance rates (leaves per tillerper day) and lower site filling (tillers per tiller per leafappearance interval) than the ryegrass species. Tillering rates(tillers per tiller per day) were also lower, except under vegetativeconditions at 4C. Low tiller number in prairie grass was notdue to lack of tiller sites but a result of poor filling ofthese sites. Lower site filling occurred because of increaseddelays in appearance of the youngest axillary tiller and lackof axillary tillers emerging from basal tiller buds. In prairiegrass, no tillers came from coleoptile buds while only occasionallydid prophyll buds develop tillers. Low tiller number in prairiegrass was compensated for by greater tiller weight. Prairiegrass had more live leaves per tiller, greater area per leafand a high leaf area per plant. Considerable variation between cultivars was found in prairiegrass. The cultivar ‘Bellegarde’ had high leaf appearance,large leaves and rapid reproductive development, but had lowlevels of site filling, tillering rate, final tiller numberand herbage quality during reproductive growth. ‘Primabel’tended to have the opposite levels for these parameters, while‘Grasslands Matua’ was intermediate and possiblyprovided the best balance of all plant parameters. prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., temperature, photoperiod, leaf appearance, leaf area, tillering, site filling, tillering sites, yield     

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 Elevated CO2 on Stomatal Size and Distribution in Perennial Ryegrass

Plants of ryegrass (Lolium perenne L. cv. Melle) were grownfrom the early seedling stage in growth cabinets at a day/nighttemperature of 20/15 °C, with a 12-h photoperiod, and aCO₂ concentration of either 340 or 680 ± 15 µl1^–1 CO₂. Young, fully-expanded, acclimated leaves fromprimary branches were sampled for length of stomata, and ofepidermal cells between stomata, numbers of stomata and epidermalcells per unit length of stomatal row, numbers of stomatal rowsacross the leaf and numbers of stomatal rows between adjacentvein ridges. Elevated CO₂ had no significant effect on any ofthe measured parameters. Elevated CO₂, Lolium perenne, ryegrass, stomatal distribution, stomatal size     

Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: II. Microclimate and Canopy Structure

Profiles of shortwave radiation, net radiation and temperaturewere measured in swards of three grasses of contrasting structureLolium perenne cv. S24, L. perenne cv. Reveille and Festucaarundinacea cv. S170. Measurements were also made of the reflectionof shortwave radiation, leaf water potential and stomatal resistance.Differences in canopy structure influenced the absorption andreflection of radiation by the varieties. The absorption ofnet radiation and its influence on air temperature inside thecanopy was shown to vary with canopy structure. Calculationsshowed that diurnal changes in the reflection and transmissionof light (400–700 nm) would have little effect on canopyphotosynthesis. No clear relationship between leaf extensionrate, temperature and leaf water potential could be established,although decreases in water potential did appear to reduce thepotential response of leaf extension rate to temperature.     

Rates of Leaf and Tiller Production in Young Spaced Perennial Ryegrass Plants in Relation to Soil Temperature and Solar Radiation

In an experiment designed to investigate the rate of leaf appearanceand tiller production in young spaced plants of three clonesof perennial ryegrass grown in the field, it was found thatthe rate of leaf appearance per tiller increased linearly withmean soil temperature up to approx. 14 °C. The rate of productionof tillers in relation to the rate of leaf appearance (sitefilling) appeared to be virtually independent of weather conditions.In plants which were adequately established, but still relativelysmall, site filling was equal to or exceeded the theoreticalsteady state; all the tiller buds which were being formed weredeveloping into visible tillers. Thus the relative rate of tillerproduction was controlled by the rate of leaf appearance. Inlarger plants site filling was less complete, and site redundancieswere probably caused by within-plant competition for light atthe tiller bases. Lolium perenne L., perennial ryegrass, tillering, leaf production, solar radiation, soil temperature