Terminal Spikelet Research Articles

Responses of Leaf and Tiller Emergence and Primordium Initiation in Wheat and Barley to Interchanged Photoperiod

The influence of constant (9, 13 and 19 h) and reciprocally-interchanged photoperiods [at terminal spikelet (TS) or triple mound (TM)] on leaf, tiller and primordium development were examined using photoperiod-responsive cultivars of spring wheat, ‘UQ 189’ and spring barley, ‘Arapiles’. In both species, constant longer photoperiod reduced the duration from sowing (S) to double ridge (DR), as expected. However, photoperiod sensitivity was not restricted to this mainly vegetative phase. There was also a marked increase or reduction in the duration of reproductive phases between TS/TM and heading (H) when plants were transferred to shorter or longer photoperiods respectively, compared with controls. These responses were largely independent of the photoperiod during previous phases although minor effects of the previous photoperiod were observed. For both species, the time course of leaf emergence was linear, or bi-linear, depending on the final leaf number on the main stem. The rate of leaf emergence was faster for the first six to eight leaves than for the leaves appearing subsequently. The rate of emergence of early-formed leaves was independent of photoperiod whereas the rate of emergence of later leaves varied with photoperiod. Photoperiod also affected the dynamics of tillering. The rate of leaf primordium initiation was little affected by variation in photoperiod, but the rate of spikelet initiation increased with increases in photoperiod. The rates of leaf and spikelet primordium initiation were both substantially higher in barley than in wheat. The fact that the reproductive phase from TS/TM to H was largely independent of the duration of the previous phase provides evidence that this phase might be genetically manipulated to increase the time for floret development and hence grain number.

Apical development in oats predicted by leaf stage

Phenological development of the shoot apex in three oat cultivars was monitored and related to the appearance and growth of leaves. Because oat leaves appear and expand differently from wheat leaves, a new continuous decimal leaf scale was developed for this purpose. There were usually two visible laminae expanding at the same time, until the appearance of the flag leaf. Thus, leaf tip number n + 2 became visible after leaf number n had reached its maximum length. The leaf stages corresponding to the formation of the flag leaf primordium (FP), double ridge (DR) and the formation of the terminal spikelet (TS) were strongly and linearly related to the final number of leaves, even though the leaf stage at any of these events varied substantially with sowing date. However, the number of leaves still to emerge after the specified apical events was nearly constant, regardless of sowing dates. The study showed that apical events can be predicted from observations of the leaf stage, provided that the final leaf number can be predicted.

Duration of the stem elongation period influences the number of fertile florets in wheat and barley.

Yield increases in temperate cereals have been associated with increases in grain number. An experiment was conducted to investigate whether altering the duration of the stem elongation period in wheat and barley increases floret fertility and thereby grain number. A photoperiod-responsive spring wheat (UQ189) and spring barley (Arapiles) were grown in a naturally lit phytotron. Plants were grown at constant (9, 13 and 19 h) and reciprocally interchanged photoperiod [at terminal spikelet (TS, wheat) or triple mound (TM, barley)] to alter the duration of the stem elongation period. An increased duration of the late reproductive phase from TS to heading in wheat resulted in more fertile florets per spike. A similar relationship was observed in barley but only for a limited range of duration of the stem elongation period. Shorter photoperiods reduced the rate of floret development and extended the time to reach the fertile floret stage. The fact that the duration of the late reproductive phase during which the spike and stem competing for assimilates was associated with the number of fertile florets per spike suggests that extending the stem elongation period in cereals could be a way to reduce assimilate competition and thereby increase the number of fertile florets and grain yield.

Free‐Air CO2 Enrichment Effects on Apex Dimensional Growth of Spring Wheat

Although primordium initiation in wheat (Triticum aestivum L.) has been extensively researched, a complete description of the growth dynamics of the apex at elevated CO2 concentrations is lacking. This study determined the rates of main stem and tiller apical elongation and widening in plants grown under two levels of CO2 concentration. Spring wheat was grown at the University of Arizona's Maricopa Agricultural Center at elevated (550 μmol mol−1) or ambient (370 μmol mol−1) CO2 concentrations. Individual plant samples were collected at different developmental stages and dissected. After dissection, the lengths and widths of the apices of the main stem (MS), coleoptile tiller (TO), primary tillers (T1, T2, and T3), and secondary tillers (T00, T01, T02, T10, Tll, and T12) were measured with a stage micrometer. Apex dimensions were fitted to an exponential model. Elevated CO2 increased the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikelet stages, and the apex widths of T2 at double ridge stage, and of T2, T3, T10, and Tll at the flag leaf appearance stage. Combining these results with a parallel study, the longer apices did not have more spikelet primordia, but wider apices had more floret primordia. Elevated CO2 changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and laterformed tillers. Earlier‐formed tillers were less responsive to elevated CO2 levels. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

A study of wheat development in the field: analysis by phases

The development of several winter and spring wheat varieties was investigated at two sites with up to eight sowing dates from 1989 to 1992. The life cycle from sowing to ear emergence was considered in phases from sowing to double ridge stage, double ridge to terminal spikelet stage and terminal spikelet stage to ear emergence, and explanations for the durations of each phase were sought in terms of thermal time, effective vernalization days and photoperiod.The life-cycle duration in thermal time from sowing until ear emergence declined as the sowing date became later. Assessed using a model function, vernalization was a major factor affecting the duration of the phase from sowing to double ridge stage for winter varieties. Some spring varieties showed small responses to vernalization. Photoperiod affected the duration of both the double ridge to terminal spikelet and the terminal spikelet to ear emergence phases. Some differences among extreme types were detected. The duration of the double ridge to ear emergence phases responded similarly to mean photoperiod in two successive years. This finding should prove useful in predicting ear emergence dates. However, the duration of double ridge to terminal spikelet and terminal spikelet to ear emergence phases at comparable photoperiods differed between years. Such differences may arise because the duration of later phases may also be affected by the environment during earlier phases, particularly the sowing to double ridge phases. Also, earlier phases affected the conditions when subsequent stages were attained; for example, the photoperiod during the double ridge to terminal spikelet phase was substantially modified by duration of the sowing to double ridge phases.In view of the importance of early stages of development in crop management techniques, the characterization of differences in response to vernalization among varieties is a priority for future research. However, progress depends on a fuller understanding of the fundamental mechanisms of response to low temperature.

Growth of Near-isogenic Wheat Lines Differing in Development—Plants in a Simulated Canopy

Abstract An understanding of the principal factors regulating the growth of temperate cereals will identify opportunities to manipulate crop growth. In an accompanying paper (Gomez-Macpherson, Richards and Masle, Annals of Botany 82 : 315–322, 1998), growth around the start of floral initiation was studied in isogenic wheat ( Triticum aestivum L.) lines grown as spaced plants. In this paper, two of the same near-isogenic wheat lines were grown as mini-canopies in a growth chamber. The objective was to determine whether results obtained using spaced plants also apply to plants grown in a simulated canopy as a first step to emulate field conditions. Biomass of plant organs, leaf area and leaf and tiller appearance were determined from sowing to ear emergence of the early developing line. Contrary to results obtained using spaced plants, lines differed in their above-ground biomass accumulation, although total plant biomass accumulation was similar. After the early line reached terminal spikelet stage (TS), biomass partitioning to the roots and leaves decreased, whereas partitioning to the stem and ear increased. This resulted in a lower root:shoot ratio in the early flowering line than in the late line which remained vegetative. Tiller senescence also began after TS in the early line whereas no tiller senescence was observed in the late line during the experiment. Furthermore, after TS, net assimilation rate was greater and leaf area ratio was lower in the early line. It is suggested that, after reaching TS, plants grown in a canopy become source limited compared to widely spaced plants, or compared to plants that have not reached TS, and this results in less root growth.

Canopy development and tillering of field‐grown crops of two contrasting cultivars of winter wheat (Triticum aestivum) in response to CO2 and temperature

Summary.Elevated CO2 (691 cf. 371 /miol CO2 mol‐1 air) and warmer temperatures (over the range 1.0UC below to 1.6oC above ambient) increased light interception by crops of two contrasting cultivars (Hereward and Soissons) of winter wheat (Triticum aestivum L.) during winter growth in the field. The fractional interception of light by the canopy increased more rapidly initially in Soissons than in Hereward, but Hereward showed a much greater response to CO2 (35% increase in Hereward but only 7% in Soissons) at 500oCd after sowing. By terminal spikelet formation, in contrast, fractional interception was greater in Hereward than in Soissons, while the effect of CO2 was the same in both cultivars (9%). Thus, although differences in the relative response of canopy development to CO2 were detected between cultivars initially, differences were negligible during later development. The greater interception of light by the canopy in elevated CO2, at any one temperature, resulted from increased tillering. The number of tillers plant“‘ at terminal spikelet was a linear function of main stem dry mass at this developmental stage but with a greater response in elevated CO2, viz 2.3 and 3.8 tillers g‐1 main stem dry mass at 371 and 691 /μmol CO2 mol‐1 air, respectively; these relations were unaffected by cultivar.

Plant development of triticale cv. Lasko at different sowing dates

The progress of leaf emergence, external morphology and apical development stages were recorded in sowings of triticale (cv. Lasko) made from February to November 1990 at Aberdeen (57° N). Leaf appearance and the number of primordia were related to thermal time (above a base of 0°C) except when photoperiods were <c. 11 h. The thermal time per phyllochron varied between leaves and the combined times for all the phyllochrons at a particular sowing accounted for the apparent response of average phyllochron to sowing date. The thermal time requirements for progression to the double ridge stage, terminal spikelet stage, onset of stem elongation and anthesis were similar except where photoperiods of <11 h occurred. The rate of grain primordium production was constant when photoperiod had been increasing at seedling emergence but the rate was reduced when the seedling experienced shortening photoperiods at emergence.

Root growth and water uptake during water deficit and recovering in wheat

Root growth and soil water content were measured in a field experiment with wheat subjected to two periods of water deficit. The first period was induced early in the season between the early vegetative stage (22 DAS) and late terminal spikelet (50 DAS), the second period at mid-season between terminal spikelet (42 DAS) and anthesis (74 DAS). Total root growth was reduced under water deficit by a reduction in the top 30 cm, while the root system continued to grow in the deeper soil profile between 30 and 60 cm. Shortly after rewatering, the growth pattern reverted to fastest root growth rates in the shallow soil layers. In relative terms, the total root system increased in relation to the above ground dry matter under water shortage. The early-, the mid-season water deficit treatments, and the control treatment had total root length of 27.4, 19.4 and 30.6 km m-2, respectively, about 2 wk before maturity. Evapotranspiration declined under water deficit, but water uptake in deeper layers increased. Water uptake per unit root length was reduced with water deficit and was still low shortly after rewatering. Remarkable was the increase in water uptake at 2–3 weeks after rewatering, both deficit treatments exceeded the control by almost 100%. This increase in water uptake followed the burst of new root growth in the upper regions of the soil. However, water uptake rates subsequently declined towards maturity, being between 0.15 L km-1 d-1 and 0.17 L km-1 d-1 for the early and mid-season water deficit treatments, slightly higher than the control, 0.12 L km-1 d-1. The results showed that the crop subjected to early water deficit could compensate for some of the reductions in root growth during subsequent rewatering, but the impact of the mid-season water deficit treatment was more severe and permanent.

Making sense of wheat development: a critique of methodology

Development in wheat is traditionally described in terms of durations of phases between observable events on the apex. The most commonly used events are seedling emergence, the formation of double ridges, and the terminal spikelet on the main stem, and the onset of anthesis. Responses of development to environmental variation is then described in terms of changes in the durations of the phases. We claim that the description itself causes confusion in describing plant responses. This is particularly because the double ridges event is not well coupled to the timing of floral development, and although the formation of the terminal spikelet is an event important for the early development of the ear, it is not a prime determinant of anthesis time. An alternative framework based on the rate of production and numbers of leaves and leaf primordia on the main stem apex, and the coordination of leaf and leaf primordium appearance, provides a simpler and more mechanistic description. We use simulations to show that such a framework explains simply the apparently complex responses of phenophase durations to the environment, and provides a basis for explaining such concepts as ‘basic development rate’ and ‘intrinsic earliness’.

Analysis of Spike Development of Three Spring Wheat Genotypes under Various Cultural Conditions

The spike development in three spring wheat genotypes was studied under various cultural conditions. Two genotypes weakly responsive to cultural conditions in spikelet number per spike (T1 from Nepal and Haruyutaka from Japan) and one weakly responsive to cultural conditions in spike length (U6 from Xinjiang Uygur district of China) were grown under three cultural conditions with different seeding density and fertilization levels : 680 seeds m−2 without fertilizer (unfavorable), 340 seeds m−2 with common fertilizer (common) and 170 seeds m−1 with double fertilizer (favorable). The durations of the vegetative phase, spikelet phase and the spike elongation phase were scarcely influenced by these cultural conditions, although the leaf number was influenced. The development of spikelets seemed to be determined by several factors other than those affecting the developmental processes of the spike. In U6, the increase in shoot apex length during the floral initiation period under the favorable condition was accompanied with an increase in double ridge number and spikelet number per spike, but such a relationship was not observed in T1 and Haruyutaka. T1 and Haruyutaka had a higher rate of spikelet formation under the favorable condition than under the unfavorable condition, but U6 showed a rather lower rate of spikelet formation under the favorable condition. Thus, the effects of the cultural conditions on the spikelet number per spike differed with genotype. At the time of terminal spikelet formation, U6 tended to have a longer spike than T1 and Haruyutaka. However, since the rate of spike elongation was higher in T1 and Haruyutaka than in U6, the spike length at anthesis was shorter in U6.

Effect of early sowing on development in wheat isolines differing in vernalisation and photoperiod requirements

The practice of sowing in early Autumn is increasing in southern Australia. For these crops, the vegetative and the spikelet initiation phases occur under higher temperature than in later sowings, whereas the period from terminal spikelet to anthesis occurs under lower temperatures. This paper studies how changing sowing time affects preanthesis phenological phases and how it can be predicted. Experiments were carried out at Condobolin and Wagga Wagga in the southern Australian wheatbelt. Five groups of isopopulations differing in phenological development were sown early (mid-April and early May), normal (late May) and late (June or later). Early sowing increased time to anthesis. Thermal time to anthesis (calculated to a base temperature of 0°C) failed to explain the differences in time to anthesis of early sown wheats. A parallel experiment carried out in growth chambers showed that the time to ear emergence of two of the isogenic groups was predominantly controlled by photoperiod, whereas in the other three groups it was predominantly controlled by vernalisation. An assessment of the cardinal temperatures used in the calculation of thermal time was carried out. By varying base and optimum temperatures of each period, it was possible to explain most variation in development of early sown spring wheats. In the lines with the strongest response to photoperiod, thermal time to anthesis increased with sowing date mainly due to a longer time to terminal spikelet stage, TT TS. A model to predict the anthesis date of these lines was proposed, based on the association between TT TS and photoperiod at double ridge. In the lines with vernalisation requirements, thermal time to anthesis increased with early sowing due to a longer vegetative phase estimated as thermal time to double ridge stage. In most of these lines, the use of photovernalising time rather than thermal time eliminated the sowing date effect on the duration of the vegetative phase.

Timing of critical developmental stages and leaf production in field-grown spring wheat for use in crop models

Detailed information on the timing of terminal spikelet formation, anthesis, maturity and the rate of leaf appearance is crucial to the predictive accuracy of the AFRCWHEAT2 growth simulation model for wheat. To obtain appropriate data under different growing conditions for two spring wheat (Triticum aestivum L.) cultivars (cvs Minaret and Canon), a main field experiment was conducted comprising eight sowing dates between mid-March and late June 1994; data from single sowings of Minaret in 1992 and 1995 were also included in the analysis. Minaret is the focus of a major European study of the impact of climate change factors on the growth and development of wheat, and data of the type reported here were essential to support the modelling aspects of the project involving AFRCWHEAT2.The accumulated thermal time from emergence to critical developmental stages was similar for all sowings of both cultivars, even though biomass was greatly reduced in the later sowings. Although final leaf numbers were comparable for all sowing dates, the rate of leaf appearance was correlated with the rate of change of day length at crop emergence in Minaret. The unmodified AFRCWHEAT2 model did not predict the timing of critical growth stages and leaf numbers well, but removal of the vernalization and photoperiod factors from the developmental sub-model greatly improved the accuracy of such predictions. These results strongly suggest that fixed quantities of thermal time may be employed successfully to predict the timing of critical developmental stages of these spring wheat cultivars over a range of sowing dates, geographic locations and climatic conditions, since development appeared to be a linear function of temperature.Despite removing the photoperiod and vernalization functions, the model consistently over-predicted final leaf number because leaf production by the model continued until 1·8 phyllochrons before anthesis, as compared to the three phyllochrons actually recorded for Minaret. AFRCWHEAT2 could therefore be further modified to reproduce more accurately the smaller number of leaves typical of these spring cultivars.

Early prediction of spring wheat yields in Saskatchewan from current and historical weather data using the CERES-Wheat model

Wheat yields were simulated at three locations in Saskatchewan (Swift Current, Saskatoon and Melfort) using the CERES (crop estimation through resource and environment synthesis-wheat)-Wheat model. The simulations were made using climatic data of selected (base) years from the start of the growing season up to the prediction date; data for the remainder of the season (runout data) were taken from 1960–1990 climate records. Years corresponding to the first, second, and third quartile yield values were selected for the three study sites. Predicted yields were calculated as the means of the yields for the runout years, and were made at five growth stages: (i) emergence; (ii) terminal spikelet initiation; (iii) end of vegetative growth; (iv) start of ear growth; and (v) start of grain filling. Predictions using this method were found to agree well with measured data, suggesting that simulations made using a combination of historical climate records and current weather data as inputs provide good indications of yield. Use of these predictions would allow producers and those in agribusiness to choose alternative actions for minimizing losses when yield prospects are poor.

CO2Effects on Phasic Development, Leaf Number and Rate of Leaf Appearance in Wheat

It has been predicted that the concentration of CO 2 in the air could double during the 21st century. Though it is recognized that CO 2 -doubling could increase yield through its effects on plant photosynthesis and stomatal behaviour, it is unclear whether CO 2 -doubling will change phasic development in wheat. A phytotron study was conducted with two contrasting cultivars of wheat, Condor (spring) and Cappelle Desprez (winter), to determine whether development is affected by a season-long exposure to 360 and 720 ppmv CO 2 . Plants were vernalized for 50 d (8/4 °C, 8 h photoperiod) before their exposure to the CO 2 treatments. There were significant differences between cultivars in the duration of different phenophases as well as in the final number of leaves. However, CO 2 concentration had no effect in either cultivar on the duration of the early developmental phase to terminal spikelet initiation, or on the final number of leaves, though CO 2 -doubling did slightly increase the later phase from terminal spikelet initiation to heading in Cappelle Desprez. Condor and Cappelle Desprez also differed markedly in the dynamics of leaf appearance. While the former had a constant rate of leaf appearance throughout development, the latter had a fast rate initially (between leaves 1 and 7), similar to that of Condor, which was followed by a slower rate after the appearance of leaf 7. Overall, CO 2 -doubling did not significantly affect the rates of leaf appearance nor the shape of the relationship. Phyllochron for the first seven leaves was the same for both CO 2 concentrations. However, the change in phyllochron associated with CO 2 -doubling for leaves 7–12 in Cappelle Desprez, although quite small (4%), accounts for part of the slightly increased duration of the phase from terminal spikelet initiation to heading under high CO 2 concentration in that cultivar. We conclude that CO 2 concentration does not influence development in wheat to a degree relevant to agronomy.

Developmental and tillering responses of winter wheat (Triticum aestivuni) crops to CO2and temperature

SUMMARYWinter wheat (Triticum aestivumL., cv. Hereward) was grown in the field within four double-walled polyethylene-covered tunnels along which near-linear temperature gradients were imposed at normal atmospheric or at an elevated CO2concentration (c.700 μmol mol−1CO2) in 1991/92 and in a further experiment in 1992/93. Development was more rapid the warmer the temperature. In 1991/92 an increase in mean seasonal temperature of 3·5 °C reduced the duration from sowing to harvest maturity (the stage when grain moisture content reduced naturally to 15–18%) byc.38 days, and reduced the duration from the double ridge stage to harvest maturity byc.34 days. A similar difference resulted from only 1·6 °C warming in 1992/93. Although the range of mean seasonal temperatures differed between years, the relation between temperature and rate of development from sowing to harvest maturity was common to both years (base temperature, −0.8 °C; thermal time 2410 °C d). Carbon dioxide concentration had no effect on this relation or on that between temperature and the rate of development from sowing to the double ridge stage and from the double ridge stage to harvest maturity. Carbon dioxide enrichment increased tillering substantially in 1991/92; there were 200 more shoots m−2at terminal spikelet formation in crops grown at elevated compared to normal CO2(additional shoots were principally coleoptile tillers and those developing after tiller 2) and this difference was reduced to 100 shoots m−2approaching harvest maturity (additional shoots remaining were those developing after tiller 2). In contrast, no effect of CO2enrichment on tillering was detected at any stage of development in 1992/93. The number of tillers per plant at terminal spikelet formation was a linear function of main stem dry weight at this developmental stage; this relationship was not affected by year or CO2. As CO2enrichment increased main stem dry weight in the first year only, when main stem dry weights at normal CO2were only one half of those values determined in the following year, it is concluded that any benefit of increase in CO2concentration to tillering in winter wheat may be greatest in those crop production environments where main stem dry weights at terminal spikelet are least andvice versa.

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.

Responses to photoperiod change with phenophase and temperature during wheat development

This paper describes responses of four wheat genotypes to photoperiod in terms of several numerical parameters and examines how they are changed by temperature and stage of development. The cultivars are an awned selection of Sunset, Condor, Rosella and Cappelle Desprez. The three phenological phases were to double ridge (Phase I), from then to terminal spikelet (Phase II) and from then to heading (Phase III). Photoperiod regimes included a 9-h sunlit treatment and five longer photoperiods achieved by extension with low-intensity incandescent lamps to 12, 15, 17, 19 and 21 h. Temperature regimes were sinusoidal with daily maxima/minima of 16 12 and 21 17 ° C . The parameters were adapted from those used in models by Major and Roberts et al. and partitioned responses into one or two photoperiodic sensitivities (Ps and Ps 2), an actual maximum length of the phase (Lm a), which occurs at the critical photoperiod (Pc), a potential maximum length (Lm p) and a basic length (Lb) that occurs at and above the optimum (Po) photoperiod. Development in all phases was modified by photoperiod, temperature, cultivar and their interactions. Regardless of phase, Po was always longer at the higher temperature though it differed among cultivars and tended to be longer in late development. Photoperiod sensitivity could be described by a single parameter (Ps) during Phase I when all responses were quantitative. However, as development progressed, sensitivity also increased, particularly at short photoperiods and in the most sensitive cultivars, for which the model required a second sensitivity parameter (Ps 2) 3–5 fold larger than Ps. During the last phase, some photoperiodic responses became qualitative. It is concluded that (i) differences among cultivars in response to photoperiod can be conveniently partitioned into parameters to describe photoperiodic sensitivity, (ii) the parameters appear to be unrelated, suggesting that plant breeders could manipulate them independently to tailor cultivars for particular environments, (iii) the parameters are sensitive to temperature, thus precluding extrapolations from one thermal environment to another and (iv) the lengths of all three phenological phases examined were affected by photoperiod, with that of the final phase being more sensitive than the early phase to double ridge.

Effects of shading in different developmental phases on biomass and grain yield of winter wheat at ambient and elevated CO2

ABSTRACTWinter wheat (Triticum aestivuin cv. Mercia) was grown in a controlled‐environment facility under simulated Held conditions at ambient (360μmol mol−1) and elevated (690 μmol mol−1) CO2 concentrations. Some of the plants were shaded to mimic cloudy conditions during three periods of about 20d duration between terminal spikelet and start of grain‐fill, giving 16 treatments in all. Elevated CO2, increased grain yield by about 20%, while shading in any period decreased yield, with the greatest effect in the last period, encompassing anthesis. No interactions between these effects were significant for grain yield, but there were complex interactions for mean grain size. Observed effects of shading and elevated CO2 on biomass production were well predicted by a simulation model. Observed effects of treatments on yield could be related to effects on biomass using a simple model which assumes that yield is proportional to biomass production, with coefficients of 0.42 (g grain yield g−1 biomass) for the first two periods and 0.74 for the last period. Wheat models should therefore include developmental changes in sensitivity of yield to biomass production, but biomass changes induced by different CO2 concentrations or light environments can be treated as having equivalent effects on grain yield.

Temperature, Nitrogen, and Carbon Dioxide Effects on Spring Wheat Development and Spikelet Numbers

Spring wheat (Triticum aestivum L.) responds favorably to elevated atmospheric carbon dioxide concentration ([CO2]) at optimum temperatures. Predictions are for air temperatures to increase as global [CO2] increases. Since spring wheat grain yields generally decline as temperature increases, there is a need to understand the effects of both [CO2] and temperature on spring wheat growth, development, and yield potential. Objectives were to evaluate combinations of [CO2], air temperature, and applied N levels on leaf and apex development, spike components, tiller numbers, dry matter, plant height, and water use in spring wheat. ‘Amidon‘ spring wheat was grown in controlled environment chambers at all combinations of 350, 650, and 950 μL L−1 [CO2], 0, 100, and 300 kg N ha−1, and 14/18°C and 22/26°C night/day air temperatures. Temperature affected the Haun stage by growth degree‐days (GDD) relationship more than N or [CO2]. The phyllochron in GDD was greater for plants grown at 22/26°C (433 GDD) than at 14/18°C (345 GDD). The Haun stage at apex double ridge and terminal spikelet increased as applied N and [CO2] increased. Fertile spikelet numbers increased as [CO2] and N level increased at 14/18°C, but at 22/26°C, spikelets increased as N increased and decreased as [CO2] increased. Fertile spikelets were greatest at 14/18°C 18°C and 650 μL L−1 [CO2]. Results suggest that at elevated [CO2] and adequate soil water, air temperature is more important than [CO2] in controlling grain yield potential. Because wheat yield potential at higher temperatures decreased as [CO2] increased, a northly shift in the spring wheat growing areas may occur if global temperatures increased in concert with [CO2].