Primary Tillers Research Articles

Free‐Air CO2 Enrichment Effects on Rate and Duration of Apical Development of Spring Wheat

Rates and durations of individual phases of wheat (Triticum aestivum L.) apical development are among the most important factors that determine yield components. Because atmospheric CO2 has been increasing steadily, it is important to evaluate the effects of elevated CO2 on wheat development. This study was conducted to determine rates and durations of leaf, spikelet, and floret primordium initiation in a Free‐Air Carbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two CO2 concentrations were 550 (elevated) and 370 (ambient) μmol mol−1 CO2. Individual plant samples were collected every 3 to 4 d. We dissected the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, Tll, and T12) and counted primordia. Apex primordium data were fitted to a four‐piece linear‐spline segmented regression model with the SAS proc NLIN. No influence of elevated CO2 (550 μmol−1 on leaf primordium initiation of MS was detected. Nevertheless, CO2 enrichment significantly increased rates of spikelet primordium initiation of MS, T1, T2, T10, and Tll, and diminished the durations of spikelet development phase of MS, TI, T2, T3, T10, and T11. Within the floret phase, CO2 enrichment significantly increased rates of floret primordium initiation of MS, TO, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

Winter Rye Leaf Emergence and its Relationship to the Phyllochron

Winter rye (Secale cereale L.) is a high‐tillering cereal crop. Understanding the relationship between the phyllochron for mainstem leaves and that of tillers is useful in adequately describing plant development and selecting crop management strategies. This study was conducted to determine the phyllochrons of conventional height (CH) and semidwarf (SD) genotypes of winter rye and the relationship of the phyllochron of mainstem leaves to that of primary tillers. Three CH and two SD genotypes were planted in a controlled‐environment growth room. Leaf stages were determined with the Haun scale and the phyllochron calculated as the inverse of the slopes of linear regressions of Haun stage to growing degree‐days (GDD). For both CH and SD genotypes, the Haun stage increased linearly with GDD, and the phyllochron was constant in the pre‐vernalization (0 < GDD ≤ 266) and vernalization (266 < GDD ≤ 566) periods. During post‐ vernalization (566 < GDD ≤ 914), the phyllochron for the mainstem increased with GDD. Leaves on the coleoptile tiller (TO), T1 (the tiller from leaf no. 1 of the mainstem), and T2 had mean phyllochrons similar to that for the mainstem. Leaves on higher positioned tillers (T4, T5) had greater phyllochron than the earlier tillers. The higher positioned tillers also required more thermal time units to emerge than the earlier tillers. To precisely describe winter rye development using the phyllochron, one should consider that the phyllochron changes with leaf and tiller position on the culm.

Effects of Combined Practice of Nitrogen Application Regime with Sparse Planting on the Growth and Yield of Rice.

Rice cultivars Akitakomachi and Hitomebore were cultivated in the field using an on-farm developed system ; no basal dressing of nitrogen combined with sparse planting (Exp plots). Their growth and yield were analyzed as compared with rice cultivated by general practice (Cont plot) with respect to the improvement of yield. In the Exp plots, nitrogen application was omitted at basal dressing but carried out as top dressing from 8th leaf age onward. Compared with the Cont plot, leaf expansion and tillering in the Exp plots were slower, the maximum leaf area index being about 4, whereas it was about 6 in the Cont plot. In the Exp plots, the percentage of fruitful culms was relatively large, but the panicle number m-2 was small, which resulted in a small spikelet number, less than 30, 000. The percentage of ripened grains was significantly larger, but the yield was 5-10% lower than that of the Cont plot. The panicle number per hill of primary tillers was not largely different among the plots, but that of secondary tillers was relatively large in the Exp plots. The fruitful culms of both primary and secondary tillers appeared to develop from upper node orders in the Exp plots as compared to the Cont plot. The panicles of secondary tillers in the Exp plots were larger than those in the Cont plot with respect to panicle weight, panicle length and leaf weight per panicle. Relative light intensity in the canopy was significantly larger at both booting and middle ripening stages in the Exp plots as compared to that in the Cont plot.

Growth and yield of winter wheat (Triticum aestivum) crops in response to CO2and temperature

SUMMARYCrops of winter wheat (Triticum aestivumL. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at eitherc.350 or 700 μmol mol−1CO2in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45% greater at elevated CO2in the first year due to more tillers, and was 30% greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO2treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6–31% greater at elevated compared with normal CO2and was also affected by a positive interaction between temperature and CO2in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO2concentrations. A 7–44% greater seed dry weight at elevated CO2in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72% at elevated CO2, because grain numbers per ear did not decline with an increase in temperature at elevated CO2. Grain numbers were reduced by temperatures > 31 °C immediately before anthesis at normal atmospheric CO2in 1992/93, and at both CO2concentrations in 1991/92. To quantify the impact of future climates of elevated CO2concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO2and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO2concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO2doubling are offset by an increase in mean seasonal temperature of only 1·0 °C to 1·8 °C in the UK.

Panicle emergence of tiller types and grain yield of tiller order for direct-seeded rice cultivars

Grain yield of rice ( Oryza sativa, L.) tillers is critical to rice crop yield and quality but relatively little is known about variations that occur among panicles and grains for tiller types and emergence orders of direct-seeded rice cultivars. The objective of research was to examine how tillering may affect yield and quality at low plant population densities with profuse tillering. Single rice plants were grown in pots in a greenhouse in 1990 and in 1992 and in the field in 1991. The aim was to maximize tillering and thus better see effects of tiller emergence order and type on yield and panicle emergence. Culm and panicle emergence dates were successively later for primary, secondary, and tertiary tillers but with a smaller delay among panicle emergence dates than was observed for tiller emergence. Grain yield of tillers was related more to emergence order than to tiller type. Secondary and tertiary tillers in sufficient numbers could cause delays in crop grain maturity. Specifically, the beginning of grain-filling (closely following top anthesis) was 1 to 5 d later for primary tillers and 3 to 9 d later for secondary tillers, compared to main stems. These data indicate direct-seeded rice cultivars have partial but not complete synchrony of panicle emergence. Consequently, production strategies that increase preflood N to increase tillering in thin (sparsely populated) rice stands, could potentially delay maturity of the crop as well as increase yields.

Growth and yield of modern deepwater rice: Comparisons with modern irrigated rice

Deepwater rice (DWR) is grown in flood-prone areas at water depths of 50 to 100 cm or more. Growth and yield of two modern DWR cultivars grown at a water depth of 80 cm were compared with high-yielding irrigated rice grown at 10 cm water depth during the wet season. Plant types of DWR which differed in tillering characteristics were produced by growing plants at different densities, and these were compared with irrigated rice cultivars to try and identify ideal plant types for DWR. Yield was higher in DWR plants (cv. HTA60) with large numbers of mainstems per unit area and no nodal tillers. HTA60 with many mainstems yielded more than 5 t ha −1 during the wet season, similar to the yield of irrigated rice (cv. IR 72) grown under the same nutrient inputs. Yield of DWR planted at different densities was positively correlated with LAI at flowering ( r 2 = 0.87), total dry matter at harvest ( r 2 = 0.82), number of spikelets m −2 ( r 2 = 0.90) and number of mainstems m −2 ( r 2 = 0.76). While nodal tillering ability is an important trait for DWR in the event of stem reduction due to damage, DWR crops with a large portion of nodal tillers always had smaller LAI and lower yields than crops with no nodal tillers. In experiments where there was no stem damage and differences in LAI were accounted for, nodal tillers had no effect on yield as indicated by (i) the same yield/LAI in one field experiment and (ii) the same yields when plants with different portions of nodal tillers were grouped into canopies at flowering at either small or large LAI (LAI = 3 or 6). Ideal DWR plant canopies shown here have high densities and large LAI, and this is associated with plants that have a large portion of mainstems or primary tillers and no nodal tillers. Results are compared with other research where productivity of DWR and irrigated rice are grown in the field.

Mow-kill Regulation of Winter Cereals for Spring No-till Crop Production

Field studies determined the influence of developmental stage on mow-killing of winter wheat and rye. Both crops were clipped at either three or four different growth stages in 1992 and 1993. When mowed at first node, wheat biomass was 4350 and 1970 kg/ha in 1992 and 1993, respectively. At this stage, primary tiller apices were below 10 cm and regrowth was vigorous. Mowing prior to 75% heading consistently yielded more than 1000 kg/ha regrowth 8 wk later. Wheat cut after flowering produced 15 460 and 9160 kg/ha dry matter in 1992 and 1993, respectively, but less than 30 kg/ha total regrowth. At first and second node, rye produced 4440 and 1800 kg/ha biomass in 1992 and 1993. When mowed belore boot, more than 50% of the total rye biomass was due to regrowth. Rye mowed at boot yielded 6940 and 3740 kg/ha in 1992 and 1993 respectively, and regrowth measured 780 and 910 kg/ha 8 wk later. Mowing after flowering resulted in no measurable regrowth. Soil temperature and PAR were affected by mow-kill date and biomass. Biomass at first mowings (first and second node) in both wheat and rye reduced seasonal soil temperatures 3.5 C compared to bare soil temperatures; while biomass at kernal-filling lowered temperatures 6.0 C. Measured 8 wk after mowing, first node mowings absorbed between 55% and 70% PAR, while plants mowed at kernal-filling absorbed less than 5%.

Annual Ryegrass Seed Yield Response to Grazing during Early Stem Elongation

AbstractSpring grazing annual ryegrass (Lolium multiflorum Lam.) seed fields with sheep (Ovis aries) is a common practice. The effects of grazing duration in early stages of stem elongation on seed yield and its components are not well known. We studied four durations of spring grazing annual ryegrass with sheep over a 2‐yr period on an Argiaquic Xeric Argialboll soil. Grazing was begun before onset of stem elongation. Treatments were no grazing (G0) and grazing until one‐third (G1), two‐thirds (G2), or all (G3) primary tillers had their apical meristems removed. Leaf area was progressively reduced by grazing duration. The number of fertile tillers increased with grazing duration in the first year, but the effect was not significant in the second year. Grazing did not affect the number of spikelets per spike or florets per spikelet in the first year. In the second year, G2 and G3 reduced spikelets per spike and had no effect on the number of florets per spikelet, whereas G1 did not affect either character. Both G2 and G3 decreased seed weight in the first year, while G1 had no effect; treatments did not affect seed weight in the second year. Grazing treatment did not affect total herbage dry matter at seed maturity, seed yield, or seed quality in either year. We conclude that, in western Oregon, grazing annual ryegrass in late winter and early spring up to the time when the apical meristem of all primary tillers are removed (G3) does not reduce seed yield. Grazing until about one‐third of primary tillers lose their apical meristem (G1) may actually improve seed yield.

Variation in Tillering and Geographical Distribution of Foxtail Millet(Setaria italica P. Beauv.).

Detailed analysis of tillering in foxtail millet (Setaria italica P. Beauv.) was carried out. The tiller development in 16 strains was observed throughout the growing season. Strains were classified into four tillering types, Type I, Type II, Type 111 and Type IV. Type I strains had the largest number of tillers with many primary tillers on the main culm, and further secondary and tertiary tillers. This tillering pattern is very similar to that of green foxtail (S. viridis P. Beauv.), the probable ancestor of foxtail millet. Strains of Type 11 produced only one or two primary tillers and no secondary tillers. Type 111 strains were non-tiller-ing and produced only one panicle on the main culm. It is supposed that Type I, which having high tillering capacity, was the first type domesticated from green foxtail. Types II and 111 subsequently differentiated from Type I by obtain-ing strong apical dominance.

Hypersensitive reaction and induced resistance in rice against the Asian rice gall midge Orseolia oryzae

AbstractRice seedlings of the resistant variety Phalguna showed premature tillering, browning of central leaf, and tissue necrosis at the apical meristem following artificial infestation with avirulent biotype 1 of the Asian rice gall midge, Orseolia oryzae (Wood‐Mason) (Diptera: Cecidomyiidae). Tissue necrosis representing a typical hypersensitive reaction (HR), accompanied by maggot mortality, was observed within 4 days after infestation. However, reinfestation of secondary tillers subsequent to HR in primary tiller, did not lead to HR in secondary tillers though maggot mortality was seen. Artificial infestation with the weed gall midge O. fluvialis did not result in HR either in gall midge susceptible TN 1 or resistant Phalguna rice varieties. Resistance in Phalguna against the virulent biotype 4 could be induced by either prior, simultaneous, or subsequent infestation with the avirulent biotype 1. The duration of effectiveness of such induced resistance varied with the sequence and time lag between infestations.

Morphological Studies on the Regularity of Shoot Development in Rice Plants. VI. The regular relationship between leaf primordia developments in the main shoot and primary tiller buds.

Rice cv. Koshihikari was seeded and grown for three years. Seedlings were dissected under a stereoscopic microscope for anatomical studies at the following stages; in n.1 age when the (n+1)-th lamina of the main shoot emerges from the n-th leaf sheath of the same main shoot, and in the middle of n.1 age and (n+1). 1 age through the vegetative phase. Appearance of a protuberance at the peripheral zone of the shoot apex was used as the sign of differentiation of a leaf primordium. Through 1.1 age to 10.1 age, the main shoot of the plant at n.1 age developed at the axil of its (n+1) leaf a hemisphere primordium which evolves into a primary tiller bud. This relationship was true for the development of the 2nd to 9th primary tiller buds. During the phyllochron (leaf emergence interval) of the (n+1) leaf, two leaf primordia for the prophyll and the 1st leaf were formed on the above tiller apex. During the three successive phyllochrons, the number of leaf primordia formed on the tiller apex was two, one and two, respectively. When the above last leaf primordium corresponding to the 6th leaf of the tiller differentiates in the third phyllochrons, the 2nd lamina of the tiller starts to emerge from its 1st leaf sheath. Generally, the 2nd to 9th tiller buds evolved into tillers.

Contribution of Individual Culms to Yield of Salt‐Stressed Wheat

Grain yield in wheat (Triticum aestivum L. emend. Thell.) is highly dependent upon the number of spike‐bearing tillers produced by each plant. Soil salinity can greatly decrease their number and productivity. Knowing the contribution of specific tillers is essential for breeding salt‐tolerant genotypes and for developing wheat growth simulation models. Our objective was to determine the effects of soil salinity on the contribution of individual culms to total grain and dry matter yields of two spring wheat cultivars, Anza and Yecora Rojo. Plants were grown in Pachappa fine sandy loam soil (mixed, thermic, Mollic Haploxeralf) in outdoor lysimeters for 2 yr. Three salinity treatments were imposed by irrigating with waters containing equal weights of NaCl and CaCl2 (electrical conductivities ≅ 1, 12, or 18 dS m‐1). Despite substantial losses in the number of tillers at moderate levels of salt stress, grain yields of the main stem (MS) and tillers Tl and T2 were as great or greater than those on nonstressed plants of both cultivars. The contribution of the MS to yield on a land area basis increased from about 25 to 35% in nonsaline treatments to over 80% with increasing salinity. The contribution of primary tillers ( ≅ 58‐65% in nonsaline conditions) decreased substantially only at the highest salinity levels. Salinity stress significantly decreased the number of spikelets per spike but the number of kernels per spike either increased or was unaffected except at the highest level of stress. Increasing salinity decreased total straw yields primarily because of fewer tillers, but dry weights of the MSs and remaining tillers were also smaller. Results show that loss of spike‐bearing tillers accounts for most of the yield reduction in salt‐stressed wheat.

Comparative Above-Ground Development Rates for Several Annual Grass Weeds and Cereal Grains

Above-ground seedling development was characterized for five annual grass weeds: downy brome, bulbous bluegrass, jointed goatgrass, Italian ryegrass, wild oat; and three cereals: winter wheat, winter barley, and winter triticale in field experiments over two years. The rate of leaf production on the main stem of each species was linearly related to cumulative growing degree days (GDD) since planting. Leaf production rates were faster for bulbous bluegrass, downy brome, Italian ryegrass, wild oat, and barley than for wheat, triticale, and jointed goatgrass. The main stem development stage when individual tillers appeared was similar in all species except under poor seedbed conditions in 1991, in which case lower-node tillers were delayed in the cereals and jointed goatgrass, but not in most of the weed species. Bulbous bluegrass, downy brome, and barley had the same percentage of plants produce the first four primary tillers on the main stem in both years; the other species showed more year-to-year variation. Seedling heights at full emergence were generally greater for large-seeded species. Small-seeded species compared to large-seeded species tended to have greater relative increases in plant height over time. Knowledge of comparative development rates between these weeds and cereals could provide information for development of growth models for each of the species and could also improve understanding of the competitive relationships between grass weeds and cereal grains.

Tiller Development in Salt‐Stressed Wheat

Wheat (Triticutna estivum L. emend Thell.) grain yields are highly dependent upon the number of spike‐bearing tillers produced per plant. Salinity, drought, and other environmental stresses can greatly affect the developmeanntd v iability of tillers. Wed eterminetdh e effects of soil salinity on the occurrence and rate of tiller development and the incidence of tiller abortion in spring wheat cultivars, Anza and Yecora Rojo. Plants were grown in Pachappa fine sandy loam soil (mixed thermic, Mollic Haploxeralf)in outdoor lysimeters. Three salinity treatments were imposed by irrigating with waters containing equal weights of NaCl and CaCl2 (electrical conductivities of ≈ 1, 12, or 18 dS m−1). Salinity significantly decreased the number of primary and secondary tillers in both cultivars. Soil waters salinities ≥7.5 dS m−1 (mean electrical conductivity of the soil water in the rootzone during tiller development SW) eliminated most of the secondary tillers and greatly reduced the number of TO, T3, and T4 tillers. However, the percentage of tillers producing spikes actually increased at SW up to 8 dS m−1. Higher salinities reduced the percentage of tillers with spikes, but not as much as the reduction in tillers. Tiller and spike production per plant decreasead bout 0.13 to 0.15 organs for each unit increase in SW. Of all the potential tillers these cultivars can produce, the primary tillers on Leaves 1 and 2 (i.e., T1 and T 2) were the least susceptible to salt stress, partly because they emerged before salinity builds up during the irrigation season. Adjusting planting densities to increase the number of anticipated spike‐bearing culms per unit area could help to maintain yields on salt‐affected soils.

Irrigation and Culm Contribution to Yield and Yield Components of Winter Wheat

AbstractWater is generally the limiting factor in U.S. Great Plains wheat (Triticum aestivum L.) production. With increasing demands for limited water, improving the efficacy of irrigation is critical. One technique is to irrigate during responsive stages of crop development, but few studies have examined this approach. This 2‐yr study on a Nunn clay loam soil (fine, montmorillonitic, mesic Aridic Argiustoll) was designed to examine the effects of irrigation, based on stage of crop development, on winter wheat yield, yield components (on a plant basis), and specific culm responses. In the first year, the treatments were control (dryland), and irrigation at late jointing. In the second year, the treatments were dryland, irrigation at late jointing, irrigation at anthesis, and irrigation at both late jointing and anthesis. Irrigation at late jointing or anthesis significantly increased grain yield and the most important yield component (spikes per plant), as well as spikelets per plant, number of kernels per plant, and kernel weight per plant. The increased spikes per plant in the irrigation treatments, particularly with late‐jointing irrigation, was due to reduced tiller abortion. Increased yield was primarily due to the contribution of more secondary tillers (T10, T11, T20, T21, T30, and T31) that produced spikes. The contribution of main stems to the total yield decreased from 92% to at most 86% with irrigation, although the dry weight of main‐stem spikes increased with irrigation. The contribution to total yield of the main yield‐producing tillers, Tl and T2, decreased from 20 to 15% and 19 to 15%, respectively, with irrigation. As with main‐stem spikes, irrigation also increased T1 and T2 spike dry weight. Therefore, the production of secondary spikes due to irrigation treatments was not at the expense of main stem or primary tiller spikes. If only one irrigation can be applied, irrigation at late jointing is recommended for central Great Plains conditions, due to its greater effect on tiller survival. This implies that developmental and physiological processes at late jointing are critical in determining final grain yield, and water stress should be avoided at this growth stage.

Effect of Tiller Trimming on Phyllochron and Tillering Regulation during Tall Fescue Development

Tall fescue (Festuca arundinacea Schreb.) seedlings grown in controlled‐environment chambers experience a rapid decrease in the rate of leaf and tiller appearance about 30 to 35 d after planting (DAP). A tiller‐trimming experiment was conducted to determine the cause of this decrease and to examine the interrelationship between leaf and tiller appearance and growth. Each primary tiller from three tall fescue populations differing in tillering capacity was trimmed 5 d following its appearance, then regrowth was removed twice weekly. Trimming tillers increased the number of tillers per plant by 29 to 134%. Plants with trimmed tillers had higher leaf appearance and elongation rates than controls after 30 to 37 DAP. Higher leaf appearance rates increased the potential number of tillers per plant by 185 to 273%. Tiller trimming did not affect the proportion of potential sites which produced tillers (site usage) in two of the three populations, but reduced site usage from 0.66 to 0.58 in the population with the highest tillering capacity. Increased tiller production was primarily due to increased production of potential tiller sites. Leaf appearance rate depended on duration of leaf tip elongation within the whorl, and on the timing of leaf initiation. Increasing the duration of leaf elongation increased the interval between initiation of successive leaves and decreased leaf appearance rate. The main stem was apparently able to support initiation of all tillers on the plant while maintaining high leaf elongation rates, suggesting that competition with main stem leaves was not limiting tiller appearance.

Epidermal Cell Division and the Coordination of Leaf and Tiller Development

Initiation and development of grass leaves and tillers are often described individually with little attention to possible interrelationships among organs. In order to better understand these interrelationships, this research examined epidermal cell division during developmental transitions at the apical meristem of tall fescue (Festuca arundinacea Schreb.). 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 determined for 0·5 mm segments along the basal 3 mm of each leaf and tiller. Primordia development and onset of rapid leaf elongation were characterized by an increase in the number of cells per epidermal file with mean cell length remaining near 20 μm per 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. Ligule formation, marking the boundary between blade and sheath cells, occurred prior to leaf tip emergence above the whorl of older sheaths, while the earliest differentiation between blade and sheath cells probably began when leaves were < 1 mm long. Major transitions in leaf and tiller development appeared to be synchronized among at least three adjacent nodes. At the oldest node, cessation of cell division in the leaf sheath was accompanied by initiation of cell division and elongation in the associated tiller bud. At the next younger node the ligule was being initiated, while at the youngest node cell division commenced in the leaf primordium, as elongation of a new leaf blade began. This synchronization of events suggests a key role for the cell division process in regulating leaf and tiller development.

Leaf Emergence of Spring Wheat Receiving Varying Nitrogen Supply at Different Stages of Development

We examined effects of nitrogen (N) supply on leaf emergence of spring wheat (Triticum aestivum L.) grown in sand with nutrient solution containing different N concentrations (9NO3: 1NH4). In expt 1, the cultivar 'Gamenya' received nutrient solution twice weekly containing a constant N supply ranging from 50 to 2400 microM N. In expts 2 and 3, cultivars 'Aroona' and 'Gamenya' were irrigated hourly with nutrient solution containing either low (L = 50 micrroM N) or high (H = 2000 microM N) N supply. In expt 2, the N supply to half of the plants receiving L and H was changed at the double ridge stage of apical development, producing plants receiving LL, LH, HL and HH. In expt 3, N supply was changed firstly when the main stem apex was vegetative (one to two leaves) and secondly when the main stem apex was at double ridge stage (four to five leaves), producing plants receiving LLL, LHL, HLH and HHH. Leaves on the main stem and primary tillers were counted. Rate of leaf emergence was estimated from regression of number of leaves against thermal time; the phyllochron was calculated as 1/ rate of emergence. Severely N-deficient plants (which had at least a 60 % reduction in shoot dry weight) had slower rates of leaf emergence (expt 1). Fluctuating N supply sometimes, but not always, changed the rate of leaf emergence (expts 2 and 3). The N supply before double ridge stage had bigger effects on the phyllochron than that afterwards (expt 3). The phyllocrons of the main stems were generally lower than those of tillers, with a greater difference between stems in N-deficient plants. Low N supply at the vegetative apex stage decreased the total number of leaves on the main stem, while low N supply after double ridge did not.

Leaf Emergence of Spring Wheat Receiving Varying Nitrogen Supply at Different Stages of Development

We examined effects of nitrogen (N) supply on leaf emergence of spring wheat (Triticum aestivum L.) grown in sand with nutrient solution containing different N concentrations (9NO3: 1NH4). In expt 1, the cultivar 'Gamenya' received nutrient solution twice weekly containing a constant N supply ranging from 50 to 2400 μM N. In expts 2 and 3, cultivars 'Aroona' and 'Gamenya' were irrigated hourly with nutrient solution containing either low (L = 50 μM N) or high (H = 2000 μM N) N supply. In expt 2, the N supply to half of the plants receiving L and H was changed at the double ridge stage of apical development, producing plants receiving LL, LH, HL and HH. In expt 3, N supply was changed firstly when the main stem apex was vegetative (one to two leaves) and secondly when the main stem apex was at double ridge stage (four to five leaves), producing plants receiving LLL, LHL, HLH and HHH. Leaves on the main stem and primary tillers were counted. Rate of leaf emergence was estimated from regression of number of leaves against thermal time; the phyllochron was calculated as 1/ rate of emergence.Severely N-deficient plants (which had at least a 60% reduction in shoot dry weight) had slower rates of leaf emergence (expt 1). Fluctuating N supply sometimes, but not always, changed the rate of leaf emergence (expts 2 and 3). The N supply before double ridge stage had bigger effects on the phyllochron than that afterwards (expt 3). The phyllocrons of the main stems were generally lower than those of tillers, with a greater difference between stems in N-deficient plants. Low N supply at the vegetative apex stage decreased the total number of leaves on the main stem, while low N supply after double ridge did not.

Epidermal Cell Division and the Coordination of Leaf and Tiller Development

Initiation and development of grass leaves and tillers are often described individually with little attention to possible interrelationships among organs. In order to better understand these interrelationships, this research examined epidermal cell division during developmental transitions at the apical meristem of tall fescue (Festuca arundinacea Schreb.). 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 determined for 0.5 mm segments along the basal 3 mm of each leaf and tiller. Primordia development and onset of rapid leaf elongation were characterized by an increase in the number of cells per epidermal file with mean cell length remaining near 20 microm per 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. Ligule formation, marking the boundary between blade and sheath cells, occurred prior to leaf tip emergence above the whorl of older sheaths, while the earliest differentiation between blade and sheath cells probably began when leaves were < 1 mm long. Major transitions in leaf and tiller development appeared to be synchronized among at least three adjacent nodes. At the oldest node, cessation of cell division in the leaf sheath was accompanied by initiation of cell division and elongation in the associated tiller bud. At the next younger node the ligule was being initiated, while at the youngest node cell division commenced in the leaf primordium, as elongation of a new leaf blade began. This synchronization of events suggests a key role for the cell division process in regulating leaf and tiller development.