Effect of the Duration of the Vegetative Phase on Shoot Growth, Development and Yield in Pearl Millet (Pennisetum americanum (L.) Leeke)

Craufurd, P. Q. and Bidinger, F. R. 1988. Effect of the durationof the vegetative phase on shoot growth, development and yieldin pearl millet (Pennisetum americanum (L.) Leeke).–J.exp. Bot. 38: 124–139 The duration of the vegetative phase (DVP) in millet, whichis the major cause of variation in the crop duration, has markedeffects on the number of productive tillers per plant and onmainshoot (MS) and tiller grain yield. Daylength extensionswere used to vary the DVP and the effect on factors affectingpanicle (tiller) number per plant and panicle yield examinedin millet hybrid 841A x J104, grown in the field at Hyderabad,India. Tiller appearance, shoot leaf appearance and leaf area,and stem and panicle growth, in both MS and primary tillers(PTs), were monitored at frequent intervals over the season.At maturity grain yield per shoot was measured The concept of thermal time was used to describe shoot development.The rates of tiller appearance and shoot leaf appearance werelinearly related to thermal time and were not affected by DVPtreatments. The duration of the growth phase from panicle initiationto flowering (GS2) and from flowering to maturity (GS3) was320 and 390 degree days (°Cd), respectively. There was nodifference in rates of leaf or tiller appearance or developmentbetween MS and PTs. Tiller appearance, tiller leaf appearanceand tiller apical development all ceased at the same time inthe later initiated PTs, approximately 550 °Cd from sowing,shortly after rapid stem growth had begun. Tillers that didnot survive were all vegetative or in the early stages of reproductivedevelopment at this time The rate of accumulation of dry matter per plant was similarin all DVP treatments, but in the longer DVP treatments a greaterproportion of the dry matter was partitioned to the MS. Mainshootstem and panicle growth rates were increased by a longer DVP,as was grain yield on the MS, and these were related to increasedMS leaf area. Concurrently, growth rates and yields in laterinitiated tillers were reduced in relation to their leaf areas.Stem growth rate was proportionately increased more than paniclegrowth rate in the longer DVP treatments and this, combinedwith a longer duration of stem growth, resulted in greater stemdry matter at maturity and, therefore, in reduced harvest index.     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

Estimation of Potential Tiller Production and Site Usage During Tall Fescue Canopy Development

Tiller appearance in tall fescue (Festuca arundinacea Schreb.)occurs in an orderly, predictable manner with the potentialfor a high degree of synchronization among tillers on a givenplant. Estimates of potential cumulative tiller production (Tmax)are made for synchronous (Tmax_lx = 2^Lx+1 – 1, where Lxis the axil number of the youngest leaf on the main stem whichbears an emerged tiller) and non-synchronous (Tmax₁ = 2^L–NLAT–1,where L is the number of leaves on the main stem and NLAT thenumber of leaves above the youngest primary tiller at its appearance)conditions. A method for determining the degree of synchronizationand an equation for estimating site usage are also presented.Early in seedling development, site usage of a tall fescue populationwith high tillering capacity was near 90%, and tillering wasregulated largely by rate of tiller site formation. As the canopydeveloped the phyllochron (time between successive leaf appearances)and NLAT increased, slowing the rate of tiller production intemporal terms and in relation to leaf appearance, respectively.Beyond 45 d after planting, site usage decreased rapidly, furtherreducing tiller production. High tiller production appearedto be associated with synchronized tiller appearance, with alack of synchrony being associated with decreased site usage.Tillers formed in prophyll axils were less likely to be in synchronywith other tillers and frequently failed to appear. In contrastwith branching in dicotyledons, apical dominance appears toplay a minor role in regulating tillering in tall fescue Tillerproduction initially appears to proceed at near maximum ratesthen is down-regulated during later development by longer phyllochrons,slower rate of tiller elongation and reduced site usage. Festuca arundinaceaSchreb., tall fescue, tiller production, leaf appearance, site usage, leaf elongation rate, synchronization, phyllochron, canopy development     

The Interdependence of Tillers in Lolium multiflorum Lam.--a Quantitative Assessment

Experiments were made to determine the extent of reciprocaltransfer of products (derived from the assimilation of ¹⁴CO₂)between various parts of the young vegetative grass plant (Loliummultiflorum Lam.). When individual laminae on different tillerswere supplied with ¹⁴CO₂, 47–64 per cent of the fixedcarbon was exported after 24 h. The principal sinks were theroot system and the shoot or tiller to which the fed leaf wasattached. Other tillers also received significant quantitiesof radiocarbon. When whole tillers were supplied with ¹⁴CO₂the percentage of fixed radiocarbon exported within 24 h rangedfrom 14–31 per cent. Of this, 50–74 per cent wasrecovered from the root system (except in the case of exportfrom the youngest tiller) but exchange of material between tillersalso occurred.A reciprocity diagram is presented and it is concludedthat despite the magnitude of the exchange no tiller showedan over-all net gain or loss. The main shoot and the tillersdiffered in the extent of their carbon exchange and in theirdegree of independence. The oldest daughter tiller of the mainshoot was the most independent and the main shoot most interdependent.     

Growth and carbon allocation of Agropyron desertorum following autumn defoliation

Summary Growth and carbon allocation of a cool season tussock grass, Agropyron desertorum, following defoliation of newly initiated tillers in the autumn of 1988 and 1989 were investigated. Tiller density and mortality, reproductive shoot density, root density, biomass, individual tiller weight, carbon allocation, and soil water depletion were used to evaluate the response of A. desertorum to autumn grazing. Tiller recruitment was lower in the autumn-defoliated treatment in both years compared with the control because of the cessation of tiller development following autumn defoliation. Autumn defoliation also significantly reduced the movement of ¹³C to the roots in 1988 but not in 1989. Soils were cooler and drier in 1989. Other plant growth measurements and soil water depletion rates were not different between treatments. Autumn defoliation in 1988 did not influence tiller recruitment in the following autumn. Two consecutive years of autumn defoliation did not affect tiller overwinter mortality or peak standing crop in 1990.     

Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoides S. & H.): 4. EXTENSION OF INDIVIDUAL LEAVES

The leaf extension rate of millet plants was measured with auxanometersin temperature-controlled glasshouses. Temperature was the dominantenvironmental factor governing the rate of leaf extension. Theobserved linear relation between extension rate and meristemtemperature had a base temperature of 10 ?C and a less clearlydefined optimum of about 30–32 ?C. Leaf growth was expressed as extension per unit thermal time,mm (?C h)^–1, to examine the influence of saturation deficit,irradiance and ontogeny at different temperatures. Leaf extensionwas independent of saturation deficit below 3.0 kPA. Irradiance,ranging from 4–16 MJ m^–2 d^–1, had a greaterinfluence on the first five leaves than the subsequent onesbut there was a large effect of leaf position. The results arediscussed in relation to the growth of crop leaves in a tropicalclimate. Key words: Leaf extension, Millet, Temperature     

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

The crop growth rates and structures of three temperate foragegrasses Lolium perenne cv. S24, L. perenne cv. Reveille andFestuca arundinacea cv. S170, were examined in the field duringa summer growth period. The growth rates of the varieties wereremarkably similar at 7 g DM m^–2 day^–1. The angularstructures of the varieties were different and they varied duringthe experiment. However, these differences did not seem to affectcrop growth rates. Nevertheless, a decrease in the efficiencyof light energy conversion of approximately 24 per cent wasobserved after a change to a more prostrate form of canopy dueto lodging. There appeared to be an inverse relationship betweenthe number of tillers per unit ground area and the weight ofan individual stem. There were large numbers of relatively lighttillers in S24 whereas S1 70 had fewer but heavier tillers.Furthermore, S24 had many small leaves per unit ground areacompared with SI70 which had fewer longer leaves per groundarea and a slower rate of leaf appearance. There were diurnalchanges in the rates of leaf extension for all the varieties.The mean daily extension rates declined as the canopies developed.     

The Growth and Development of Simulated Swards of Perennial Ryegrass: I. Leaf Growth and Dry Weight Change as Related to the Ceiling Yield of a Seedling Sward

The leaf growth, tiller production, light interception, anddry weight increase of a simulated sward of S24 perennial ryegrass(Lolium perenne) were followed during the development of thesward from a collection of two-leaved seedlings to a closedcanopy with an LAI of 23, of which 15 consisted of green leaflaminae. The dry weight of live shoots increased exponentiallyat first, but then entered a long linear phase of increase.This was equivalent to a crop growth rate of 200 Kg ha^–1day^–1 and a conversion efficiency of radiant energy (400–700nm) of 7.2 per cent. Towards the end of the growth period therate of increase of live shoots declined rapidly to zero anda ceiling yield was reached equivalent to 10 metric tons ha^–1.Leaf growth continued at a high rate, but was equalled by therate of leaf death, so that the weight of live leaf tissue remainedconstant. By this time the swards had achieved a stable tillerpopulation (about 1 cm^–1), each tiller bore a constantnumber of live leaves (about three), and the length of eachnewly expanded leaf equalled the length of the old leaf it replaced(about 70 cm). The swards were grown in Perlite so that in theabsence of soil fauna dead leaves accumulated at the base ofthe sward where, after 12 weeks, they accounted for 19 per centof the total weight of dry matter produced.     

Tillering in grain sorghum over a wiide range of population densities: modelling dynamics of tiller fertility

The prediction of tillering is poor or absent in existing sorghum crop models even though fertile tillers contribute significantly to grain yield. The objective of this study was to identify general quantitative relationships underpinning tiller dynamics of sorghum for a broad range of assimilate availabilities. Emergence, phenology, leaf area development and fertility of individual main culms and tillers were quantified weekly in plants grown at one of four plant densities ranging from two to 16 plants m(-2). On any given day, a tiller was considered potentially fertile (a posteriori) if its number of leaves continued to increase thereafter. The dynamics of potentially fertile tiller number per plant varied greatly with plant density, but could generally be described by three determinants, stable across plant densities: tiller emergence rate aligned with leaf ligule appearance rate; cessation of tiller emergence occurred at a stable leaf area index; and rate of decrease in potentially fertile tillers was linearly related to the ratio of realized to potential leaf area growth. Realized leaf area growth is the measured increase in leaf area, whereas potential leaf area growth is the estimated increase in leaf area if all potentially fertile tillers were to continue to develop. Procedures to predict this ratio, by estimating realized leaf area per plant from intercepted radiation and potential leaf area per plant from the number and type of developing axes, are presented. While it is suitable for modelling tiller dynamics in grain sorghum, this general framework needs to be validated by testing it in different environments and for other cultivars.     

Response to Temperature in a Stand of Pearl Millet: VI. LIGHT INTERCEPTION AND DRY MATTER PRODUCTION

Stands of pearl millet were grown in glasshouses in which meanair temperature was controlled to 19, 22, 25, 28 and 31 ?C withan amplitude of ?5 ?C. During the main growth period, leaf areaindex increased at a constant rate which was proportional tomean temperature above a base of 10 ?C. The warmest stand, therefore,intercepted more radiation before anthesis but the transmissioncoefficient was independent of temperature (K 0.3). Based ondry weight at final harvest, the efficiency of conversion forintercepted radiation ranged from about 2.1–2.4 g MJ^–1consistent with field experience. Combining this informationwith figures for the duration of growth in relation to temperaturesuggests that growth rate should be maximal at 25–27 ?Cand total dry weight at 20–22 ?C. Key words: Temperature, Pearl millet, Growth rate, Light     

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     

Assimilate Distribution in Poa annua L.

The carbon economy of a flowering tiller of Poa annua L. hasbeen examined over the period from inflorescence emergence tograin shedding. The total import of ¹⁴C by the inflorescencereached a maximum at late grain filling but the relative importof assimilate was greatest 14 days after its appearance andrepresented 20–25 per cent of that assimilated by theinflorescence itself. The inflorescence continued to be an importantassimilatory organ after grain ripening when it exported morethan 50 per cent of its assimilate to the stem, roots and othertillers. The patterns of distribution of assimilates from the youngestuppermost and the oldest green leaf of the reproductive tillerwere largely determined by the stage of development of the inflorescence.The youngest leaf mainly supported the inflorescence up to theend of the grain-filling stage but then supplied assimilatesbasally to the roots and adjacent tillers. The oldest greenleaf supported the growth of the stem and the inflorescenceup to anthesis but after this supplied assimilates mainly tothe roots and tillers. Removal of grains or the entire inflorescence only 1 h beforesupplying ¹⁴CO₂ greatly reduced the rate of fixation of ¹⁴CO₂and the export of radiocarbon, as well as changing the patternof distribution of assimilates within the plant. The significanceof these results is discussed and comparisons made with cerealsand perennial grasses.     

Hormonal regulation of tiller dynamics in differentially-tillering rice cultivars

Tiller number can contribute significantly to yield potential of rice, but little knowledge is available on hormonal regulation of tillering and tiller dynamics. In the present study, Indole-3-acetic acid (IAA), kinetin (6-furfuryl amino purine) and Gibberellic acid (GA₃) treatments have been applied at the early tillering stage to two rice cultivars that contrast for tiller number. The responses of the hormones were studied on growth, development, grain yield, senescence patterns, assimilate concentration of the panicle and ethylene production in different classes of tillers. The leaf area, panicle grain number, fertility percentage and grain yield of tillers were higher in the low-tillering cultivar than that of high-tillering cultivar; the treatment of kinetin was more effective in the latter than in the former. High ethylene production was responsible for reduction of growth duration and grain yield of the tillers. Kinetin application reduced ethylene production of the late-tillers significantly for the benefit of grain yield.     

Variations in Tiller Dynamics and Morphology in Lolium multiflorum Lam.Vegetative and Reproductive Plants as affected by Differences in Red/Far-Red Irradiation

Lolium multiflorum Lam, plants were grown in a growth room undertwo light sources with red/far-red ratios of 1·62 and0·84 but similar photosynthetically active radiation.In both situations the capacity to produce new tillers and thelight available per tiller decreased with canopy growth. Tilleringwas further reduced by the low red/far-red ratio while lightinterception and plant dry weight were unaffected by this treatment.In both reproductive and vegetative plants under the lower red/far-redratio the time between leaf expansion and the appearance ofa tiller in its axil was increased and the proportion of ‘maturebuds’ that developed was reduced. Irradiation with lowred/far-red advanced the reproductive development and increasedthe number of fertile tillers per plant. It also caused longerleaf sheaths, blades and reproductive shoots. The results suggestthat as canopy density increases the lower light interceptionper tiller and the photomorphogenic effect of low red/far-redratios may reduce the capacity to produce new tillers. Lolium multiflorum, Lam., annual ryegrass, tillering, tiller growth, leaf growth, flowering, light quality.     

Tillering in grain sorghum over a wide range of population densities: identification of a common hierarchy for tiller emergence,leaf area development and fertility

Most studies of tiller development have not related the physiological and morphological features of each culm to its subsequent fertility. This introduces problems when trying to account for the effects of tillering on yield in crop models. The objective of this study was to detect the most likely early determinants of tiller fertility in sorghum by identifying hierarchies for emergence, fertility and grain number of tillers over a wide range of assimilate availabilities. Emergence, phenology, leaf area development and dry weight partitioning were quantified weekly for individual tillers and main culms of tillering and uniculm plants grown at one of four densities, from two to 16 plants m(-2). For a given plant in any given density, the same tiller hierarchy applied for emergence of tillers, fertility of the emerged tillers and their subsequent grain number. These results were observed over a range of tiller fertility rates (from 7 to 91%), fertile tiller number per plant at maturity (from 0.2 to 4.7), and tiller contribution to grain yield (from 5 to 78 %). Tiller emergence was most probably related to assimilate supply and light quality. Development, fertility and contribution to yield of a specific tiller were highly dependent on growing conditions at the time of tiller emergence, particularly via early leaf area development of the tiller, which affected its subsequent leaf area accumulation. Assimilate availability in the main culm at the time of tiller emergence was the most likely early determinant of subsequent tiller fertility in this study.     

Growth of Tiller Buds in Barley: Effects of Shade Treatment and Mineral Nutrition

Examination of the stem apex of Proctor barley showed that thebud of the coleoptile tiller, Tc, is probably present in thedry grain and that the bud, TI, carried in the axil of the firstleaf is present at or soon after 24 h from planting. Subsequentlytiller buds are initiated with a plastochron of about 4 days,this being rather longer than that for the foliar primordia.During the initial phase of bud growth vascular connectionsare established with the leaf above, but not to the subtendingleaf. At some time after these vascular connections are formedand when it has a dry weight of 4–7 µg the bud entersa phase of rapid, exponential growth in dry weight. Shading the first leaf delays the onset of rapid growth forboth Tc and Ti, but after a lag period rapid growth commences;this is coincident with development of the second leaf as anorgan exporting assimilated carbon. The phase of rapid growth of tiller buds is delayed when applicationof either nitrogenous or nonnitrogenous minerals is delayed.Ammonium was found to be less satisfactory as a nitrogen sourcethan nitrate, probably because of toxicity effects. Slight growthof Tc and T1 occurs in presence of nonnitrogenous minerals andabsence of nitrogen but growth is greater when nitrogen is suppliedin absence of the other minerals, although such growth is substantiallyless than that found when all nutrients are supplied. The interactionbetween nitrogen and non-nitrogenous minerals which controlsbud growth was not found to affect growth of the parent plantwhich is, as previously shown, controlled by timing of the nitrogensupply. AnotheT distinction is that higher concentrations ofnitrogen and the other minerals are required for maximum growthof the bud than for that of the plant. Tiller bud growth is interpreted as occurring in two phases.In the first, initiation, phase there is a close associationwith the subtending leaf, and nutritionally bud and leaf arelinked. This phase is followed by one in which the bud is directlyconnected by vascular traces to the leaf above, which becauseof this controls bud growth by modulating supply of assimilatedcarbon and nitrogen, and other minerals to it.     

Modification of Leaf Size in Rice (Oryza sativa L.) and its Effects on Water Stress-induced Abscisic Acid Accumulation

The ability of detached leaves of the rice cultivars IR20 and63–83 and their F₂ progeny to accumulate ABA in responseto water stress is negatively correlated with leaf size. Itwas shown that this association was not an artifact of incubationconditions following the imposition of stress. Also, it waspossible to break the correlation by selecting plants in segregatingpopulations which differed in ABA yet had similar leaf size. In further experiments, leaf size was altered phenotypicallyby various treatments; either being increased by gibberellinapplication or periodic removal of tillers, or reduced by priorexposure to water stress or ABA. Although responses to thesetreatments were complex, the results demonstrated that leafsize and accumulation capacity were at least partially independent.It is suggested that the correlations observed previously inF₂ populations from the cross IR20 x 63–83 were a resultof genetic linkage. Oryza saliva L., rice, leaf size, abscisic acid, water stress     

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     

Clonal analysis of the development of the barley (Hordeum vulgare L.) leaf using periclinal chlorophyll chimeras

Barley seedlings that show mosaic expression of chlorophyll were selected from the progenies of mutagenized seeds. The sectored plants were grown under conditions that lead to the formation of lateral tillers, and a fraction of these had different kinds of leaf variegation. These sectorially and periclinally chimeric shoots were used to analyze the cellular organization of the barley shoot apex and the clonal development of the leaf. The shoot apex is organized in two cell lineages, L1 and L2. As well as giving rise to the epidermis, the L1 layer contributes to leaf mesophyll, particularly at the margins, but, on the adaxial side of leaf laminae, also in more central positions. The L1 layer alone is responsible for the formation of the hood, a flower homologue structure present in strains homozygoous for the dominant allele at the K (hooded ) locus. The relative contribution of L2 to leaf formation decreases in younger tillers and during tiller development from the basal to the flag leaf. Chimerism of the plants was generated by non-transmissible somatic events or by nuclear mutations. Received: 28 May 1998 / Accepted: 20 July 1998     

Epidermal Cell Division and the Coordination of Leaf and Tiller Development

Initiation and development of grass leaves and tillers are oftendescribed individually with little attention to possible interrelationshipsamong organs. In order to better understand these interrelationships,this research examined epidermal cell division during developmentaltransitions at the apical meristem of tall fescue (Festuca arundinaceaSchreb.). Ten seedlings were harvested each day for a 9-d period,and lengths of main shoot leaves and primary tillers were measured.In addition, numbers and lengths of epidermal cells were determinedfor 0·5 mm segments along the basal 3 mm of each leafand tiller. Primordia development and onset of rapid leaf elongationwere characterized by an increase in the number of cells perepidermal file with mean cell length remaining near 20 µmper cell. After the leaf had lengthened to 1-1·5 mm,cells near the leaf tip ceased dividing and increased in length,at which time leaf elongation rate increased rapidly. Liguleformation, marking the boundary between blade and sheath cells,occurred prior to leaf tip emergence above the whorl of oldersheaths, while the earliest differentiation between blade andsheath cells probably began when leaves were < 1 mm long.Major transitions in leaf and tiller development appeared tobe synchronized among at least three adjacent nodes. At theoldest node, cessation of cell division in the leaf sheath wasaccompanied by initiation of cell division and elongation inthe associated tiller bud. At the next younger node the ligulewas being initiated, while at the youngest node cell divisioncommenced in the leaf primordium, as elongation of a new leafblade began. This synchronization of events suggests a key rolefor the cell division process in regulating leaf and tillerdevelopment.Copyright 1994, 1999 Academic Press Festuca arundinacea Schreb., tall fescue, cell division, leaf initiation, tillering, ligule development