Terminal Spikelet Research Articles

The inflorescences ofPaspalum (Poaceae, Paniceae): TheQuadrifaria group and the evolutionary pathway towards the fully homogenized, truncated common type

The inflorescences ofPaspalum are composed of a main axis and 1 to more than 100 raceme-like lateral branches arranged along it. Each branch bears two rows of homogeneous subunits composed either of one or two consecutive-ordered axes, each one ending with a spikelet. In terms ofTroll's descriptive and typological system, such lateral branches were regarded as long paracladia which bear homogeneous bi-axial short paracladia. The structural pattern of these long paracladia is considered to be a recapitulation of the distal main-axis structure which was lost by evolutionary truncation. — The occurrence of a main florescence (= terminal spikelet) and a short paracladia-bearing zone at the distal portion of the main axis in several species of the genusPaspalum, as it is exemplified by species belonging to the so-called ‘Quadrifaria group’, seems to support the hypothesis that the usual inflorescence ofPaspalum actually derived from a paniculate structure by evolutionary homogenization and truncation processes. This ‘Quadrifaria-type inflorescences’ would be regarded as an intermediate step in the evolutionary pathway. Nevertheless, the phylogenetic implications of this interpretation remains obscure because at the present time there is not any hypothesis about the phylogeny of the genus available.

Control of early development in winter and facultative wheats in contrasting field environments

The major factors influencing the development of wheat are responses to vernalisation and to photoperiod, and intrinsic earliness. This study sought to determine how these factors influence the development of field-grown winter and facultative wheats of Australian origin, which tend not to be highly responsive to photoperiod. Of particular interest was the relationship between response to vernalisation and the switch from vegetative to reproductive growth. The effect of these developmental factors in influencing field development was established by correlating measurements from controlled and field environments. Three field environments were studied at 2 sites, a February and an April sowing at Temora (NSW, Australia), and a November sowing at Tel Hadya (Syria). Both sites were around 35� latitude. These environments differed in the duration from sowing to the onset of vernalising temperatures in winter. The onset of vernalisation was most delayed in seedlings for the February sowing at Temora. Vernalisation commenced earliest in seedlings for the November sowing at Tel Hadya, and was then presumed to proceed most rapidly. The 3 development factors were measured in 17 wheat genotypes. These data had been published previously; however, measurements of integrated response to vernalisation were re-expressed in new units, and the experiment was repeated, to attain greater precision. Measurement of each developmental factor was correlated with the timing of double ridge, terminal spikelet, and the beginning and end of spikelet site accumulation in each field environment. Where vernalisation was most delayed after sowing, the strongest correlation was between integrated response to vernalisation and the duration from sowing to double ridge. Where vernalisation was most rapid after sowing, the strongest correlation was between intrinsic earliness and the duration from sowing to the beginning of spikelet site accumulation. This study suggests lack of vernalisation most strongly delays the timing of double ridge in winter wheats, and masks the effect of intrinsic earliness which otherwise influences early development. These findings reconcile the significance of the timing of double ridge with previous quantitative studies of early development in winter and facultative wheats.

Wheat Development as Affected by Radiation at Two Temperatures

A wheat cultivar (Condor) was grown in two experiments (thermal regimes 18/13 and 21/16°C) under low (298 μE m-2: s-1) radiation regimes during either an early phase from seedling emergence to terminal spikelet initiation (S2), a late phase from terminal spikelet initiation to anthesis (S2), or for the full period from seedling emergence to anthesis (S12), or high (560 μE m-2s-1) radiation throughout the growing period (S12) to determine whether developmental events are affected by radiation. The main developmental events considered in this study were the timing of terminal spikelet initiation and anthesis, the final number of leaf and spikelet primordia initiated in the apex and the rate of leaf appearance. Number of grains per spike and culm height were also measured. The duration of each phenophase was not affected by radiation intensity. Temperature affected the rate of wheat development, but the acceleration of development due to temperature during the seedling emergence - terminal spikelet initiation phase only slightly reduced (from 24.8 to 23.2 days). Differences in time from terminal spikelet initiation to anthesis were greater than in the earlier phases, having been the duration reduced from 24.6 to 20.0 days due to high temperature. Associated with the lack of effect of radiation on phasic development and the negligible effect of temperature on the duration of the early phases of development, final Leaf number was practically unchanged in this study by either the radiation level or the growing temperature. Thus, radiation did not affect the rate of leaf initiation. The number of spikelets was affected by neither the treatments nor the thermal environment. The rates of leaf appearance were accelerated by temperature. Radiation, on the other hand, did not significantly alter the rates of leaf appearance in any of the treatments. As expected from many sources in the literature, the number of grains per spike was significantly affected by radiation during the phase from terminal spikelet initiation to anthesis. Due to the lack of significant effects of radiation on the developmental patterns of wheat, the changes in number of grains per spike were due to changes in the number of grains born in each spikelet. The results of the present study were compared with others available in the literature on the effects (or lack of them) of radiation and CO2 concentration on phasic development, plastochron and phyllochron in wheat to reach the general conclusion that the rate of developmental events in wheat, in contrast to other plants, is almost completely independent of the availability of assimilates, with a possible exception for the Equatorial latitudes.

The influence of daylength on final leaf number in spring wheat

The influence of daylength on final leaf number was determined in four field-sown wheat cultivars with no vernalisation requirement. Leaf and primordium appearance was monitored in plots sown at two-month intervals during an annual cycle. The timing of the response to daylength varied substantially among cultivars. In one, final commitment of the last leaf primordium occurred close to the time of initiation of that primordium while, in another cultivar, commitment did not occur until terminal spikelet or later. In the other two cultivars, commitment occurred midway through spikelet initiation. Late timing of response to daylength is a useful adaptation that allows cultivars with no vernalisation response sown autumn to set more leaves than when sown in spring, and hence to delay flowering. Based on the analysis, a simple iterative procedure was developed that successfully predicted final leaf number, the dates of appearance of the flag ligule and anthesis for one of the cultivars grown in an independent experiment.

The effects of radiation and nitrogen on number of grains in wheat

SUMMARYThe possible interacting effects of shading and N supply on number of grains ofTriticum aestivumL. (cv. Buck Ñandú) were investigated at Balcarce, Argentina, during the 1988/89 and 1989/90 growing seasons. Shading was imposed fromc.13 days before anthesis to 6 days after, and four rates of N fertilization were supplied within each shading treatment around the date of terminal spikelet formation. Water and other nutrients were not limiting.Total grain yield was strongly correlated with grain number/m2, regardless of shading or N supply. At the highest N rates, grain number and dry weight of spikes at anthesis were linearly related to a photothermal quotient, i.e. the ratio of intercepted photosynthetically active radiation (PAR) to mean temperature minus 4·5 °C, during the period from 20 days before anthesis to 10 days after. The response of grain number to the photothermal quotient was interpreted in terms of the supply of assimilates to the spike at anthesis, which determined flower survival. The response of dry weight of spikes to photothermal quotient was interpreted in terms of crop growth rate since there was a linear relationship between crop growth rate and intercepted radiation. The lowest N rates reduced the number of grains/m2, at any given photothermal quotient. Since the reduction in grain number also occurred at any given dry weight of spikes, it cannot be explained by a reduced supply of assimilates to the spikes. Grain number responded directly to the supply of N to the spike, probably through the survival of differentiated flowers. The relationship between spike growth rate and crop growth rate was not affected by N supply. Crop growth rate was reduced by reduced N supply, because less radiation was intercepted and because radiation-use efficiency was lowered. These results indicate that current models for determining yield and number of grains/m2, based on crop growth, are not adequate when N is deficient.

Base and optimum temperatures vary with genotype and stage of development in wheat

ABSTRACTSome assumptions concerning development in wheat (Triticum aestivum, L.) were examined. These are that (i) the rate of development towards anthesis increases linearly with temperature, (ii) the base temperature is 0°C, (iii) the optimum temperature is above the range at which wheat is normally grown, (iv) base and optimum temperatures do not change with development, and (v) the relationships for different cultivars are similar. We tested these assumptions in studies using a naturally lit phytotron with four cultivars and six temperature regimes between 10 and 25°C. Seedlings were vernalized for 50 d and then grown under a photoperiod of 18 h to avoid confounding the responses to vernalization and photoperiod with those to temperature. In cultivars Sunset and Rosella, the rate of development for the full period to anthesis increased linearly between base and optimum temperatures. However, in cultivars Condor and Cappelle Desprez, a linear fit was not statistically acceptable. For these cultivars, the rate of development towards anthesis increased rapidly with increase in temperature from 10 to 19°C, but temperatures higher than 19°C had little or no fürther accelerating effect. When a linear relationship was fitted by ignoring data for temperatures above 19 7deg;C, base temperatures calculated for the full period to anthesis were c. 5.5, 5.5,4.0 and 2.5°C for Sunset, Condor, Rosella and Cappelle Desprez, respectively (i.e. an average value of c. 4 7deg;C). The full period to anthesis was subdivided into three phases for fürther analysis. These were (i) from the beginning of the experiment to terminal spikelet initiation, (ii) from terminal spikelet initiation to heading, and (iii) from heading to anthesis. When these sub‐phases were analysed a linear relationship was found to be appropriate for all combinations of cultivar and developmental phase. However, both base and optimum temperatures calculated from the relationships increased as development progressed from (i) to (iii). Averaging across cultivars, base temperatures for the three phases were ‐1.9, %1.2 and %8.1°C, respectively, while optimum temperatures were <22, 25 and >25°C, respectively. Cultivars differed substantially in all these parameters. The progressive increase in optimum temperature with phasic development was apparently the main reason why linear fits for the three sub‐phases became a curvilinear fit for the full phase to anthesis.

Influence of photoperiod on culm length in wheat

The effects of photoperiod on culm length (CL) were examined in a semi-dwarf (Condor) and a standard-height (Thatcher) wheat cultivar under five photoperiod regimes (natural photoperiod, two constant photoperiods, and two under which photoperiod was artificially increased over natural photoperiod by 9.8 and 13.1 min/d). The five photoperiod treatments were randomly assigned at sowing and re-randomised at terminal spikelet initiation (TS) to give five different photoperiod treatment combinations before and after TS. The cultivars differed significantly in final CL, Thatcher being taller than Condor. Culm length was related to the average photoperiod during the period between seedling emergence (SE) and double ridge (DR). There appeared to be an indirect effect of photoperiod during the vegetative phase on subsequent culm elongation, which was much stronger in Thatcher than in Condor, but the differences in CL between the two cultivars were smaller under long compared with short photoperiods. The effect of photoperiod on CL appeared to be closely related to the final number of leaf primordia on the main culm and to the number of elongated internodes, both increasing with short photoperiods. In contrast, differences in CL between cultivars were mainly due to the lengths of the internodes.

Development in wheat as affected by timing and length of exposure to long photoperiod

Seeds of a spring wheat (Triticum aestivum L. cv. 'Condor') were vernalized and then grown at 19°C in two naturally-lit environments, one with a moderate (12 h) and the other with long (18 h) photoperiod. Treatments consisted of transfers of plants from the moderate to the long photoperiod chamber on different occasions, or for periods of different durations. The main objectives were to determine whether wheat development responds to current and previous photoperiodic environments and whether there is a juvenile phase when the plants are insensitive to photoperiod. Plants under constant 18 h photoperiod had fewer leaves which appeared faster than those under constant 12 h photoperiod (i.e. phyllochron was increased from 4.4 to 5.1 d leaf -1 ). Plants transferred from 12 h to 18 h photoperiod at terminal spikelet appearance (TSA) reached anthesis 4 d earlier than plants retained at 12 h, while plants under continuous long photoperiod (18 h) completed this phase most rapidly. Thus, there was some evidence for a historic effect of photoperiod on development. Exposure to long photoperiod during the first 5 d after plant emergence accelerated the rate of development towards anthesis, suggesting that there was no juvenile period of photoperiodic insensitivity. There were, however, changes during ontogeny in the degree of sensitivity to long photoperiod, increasing from seedling emergence to a maximum c. 15 d later, and then decreasing again. Although all treatments were imposed before TSA, the response was not limited to the pre-TSA phase, suggesting that well before the terminal spikelet appeared, the plant was already committed to the initiation of this spikelet. Spikelet number decreased with delayed transfer to long photoperiod with a minimum for plants transferred to long days from 16-20 d after seedling emergence. Additionally, there was a trend for an increase in the rate of leaf appearance (decrease in phyllochron) when the plants were exposed to long days between 10 and 35 d after seedling emergence. Although the differences were small, when considered in conjunction with the effects on final leaf number they become important in explaining differences in time to anthesis.

Does temperature affect final numbers of primordia in wheat?

Photoperiod and vernalisation both affect the number of leaf and spikelet primordia and, hence, the duration of the early phases of development in wheat. Temperature also affects duration of developmental phases but it is not clear whether temperature-related changes in duration are similarly associated with final numbers of primordia. The objective of this study was to examine these temperature-related associations. A phytotron study was conducted in naturally-lit cabinets with four cultivars (Sunset, Condor, Rosella and Cappelle Desprez) and six temperature regimes between 10 and 25°C. Seedlings were vernalised for 50 days and then grown under a photoperiod of 18 h to avoid confounding the responses to vernalisation and photoperiod with those to temperature. The duration of the period of terminal spikelet initiation was reduced by increases in temperature from 10 to 19°C, but extended at temperatures above 19°C. Cultivars differed in the time taken to the terminal spikelet stage. However, final numbers of leaf and spikelet primordia were affected only marginally by temperature. Final leaf number increased slightly with temperature, but this trend was only significant in Cappelle Desprez, and in that case accounted for only 1 leaf over the 15°C range. There was a curvilinear association between final spikelet number and temperature, with an optimum at about 19°C. However, temperature changed spikelet number by a maximum of only 3 per ear. Although significant correlation was only found for leaf number, there was a general trend for a reduction in number of primordia with longer duration to terminal spikelet initiation. However, these trends were all very small. This suggests that the effects of temperature on the rate of apex development towards terminal spikelet initiation and on the rate of primordia initiation are similar. Cultivar differences in duration of primordia initiation were translated directly to differences in number of primordia initiated. The relative impact of temperature and other factors on the rates of primordia initiation and apex development towards terminal spikelet initiation were assessed using a simple model.

Rate of Leaf Appearance and Final Number of Leaves in Wheat: Effects of Duration and Rate of Change of Photoperiod

This study was conducted to test the hypothesis that photoperiod or its rate of change significantly affects the rate of leaf appearance (RLA) and final number of leaves (FNL) in wheat, as suggested from several time-of-sowing experiments. Two wheat cultivars (Condor and Thatcher) were sown in the field on 2 Sep. 1992 at Melbourne (38°S). Photoperiod was extended artificially to give five treatments up to terminal spikelet initiation (TS) viz.: natural photoperiod (rate of change of photoperiod = 2 min d-1), two faster rates of change (8·5 and 13·3 min d-1) and two constant photoperiods of 14·0 and 15·5 h. After TS, the two constant photoperiods were extended to 15·0 and 16·5 h, respectively, and treatments were re-randomised, i.e. some plots received different photoperiod regimes before and after TS.The rate of leaf appearance maintained strong linear relationships with thermal time. It was greater for Condor [0·012-0·013 (°C d)-1] than for Thatcher [0·011-0·012 (°C d)-1] and did not alter during plant development or in response to the change in photoperiod at TS. Rate of leaf appearance on the main culm was not influenced by the rate of change of photoperiod nor by the average photoperiod.Cultivar and photoperiod significantly affected FNL on the main culm. Condor produced more leaves than Thatcher under long but not under short photoperiods. The rate of change of photoperiod did not affect FNL independently of the effect of average photoperiod. Most of the variation in FNL due to photoperiod resulted from differences in duration of leaf initiation.The lack of effects of the photoperiod treatments on RLA contrast with previous reports of its effects on the rate of phasic development from seedling emergence to double ridge. Therefore, the number of visible leaves on the main culm (NL) at double ridge and at TS were not constant. However, NL on the main culm at double ridge was closely correlated with FNL.

Testing the root growth subroutine of the CERES-wheat model for two cultivars of different cycle length

Abstract The objective of this study was to test the root growth subroutine from the CERES-Wheat model during a growing season. The study involved observation and analysis of root growth and distribution throughout the growing season, and thier simulation, using two wheat cultivars of different cycle length and two water regimes. The model accurately predicted crop development and yield, but overpredicted root depth by 90 cm at terminal spikelet and by 50 cm booting, anthesis and mid grain-filling period. In addition, the model underpredicted root mass, presumably because of the way it handles root—shoot partitioning. There was good agreement between observed and simulated values of root-length density and soil water content ( R 2 = 0.66 and 0.86, respectively). The value of the specific root-length parameter in CERES-Wheat lies closer to data reported from a winter wheat crop experiment than to data from spring wheat reported in this and other studies. The model's ability to predict these attributes is discussed.

Development Rate in Wheat as Affected by Duration and Rate of Change of Photoperiod

A field study was conducted to test the hypothesis that wheat development rate responds to the rate of change of photoperiod. Two wheat cultivars (Condor and Thatcher) were sown on 18 Aug. 1992 at Melbourne (38° S). Photoperiod was extended artificially to give five treatments up to terminal spikelet initiation (TS) viz.: natural photoperiod (rate of change of photoperiod, 2·3 mind d-1), two faster rates of change (9·8 and 13·1 min d-1) and two constant photoperiods of 14·0 and 15·5 h. After TS, the two constant photoperiods were extended to 15·0 and 16·5 h, respectively and treatments were randomly re-allocated, i.e. some plots received different photoperiod regimes before and after TS.There were no significant differences among treatments in the length of the period from sowing (S) to seedling emergence (E) phase, ranging from 15 to 16·3 d. The rate of development from E to TS responded to increases in photoperiod in both cultivars, increasing with average photoperiod across all treatments but there was no effect of rate of change of photoperiod independent of its average photoperiod. The rate of development from TS to anthesis (A) did not show any trend with average photoperiod. This lack of effect of photoperiod on the period from TS to A contrasts with other results from the literature and possible reasons for this conflicting result are discussed. Rate of change of photoperiod did not affect the duration of the phase from TS to A either. Therefore, the effect of photoperiod on the duration of the S-A period was strongly and positively correlated to that of the length of the E-TS phase.

Variation in temperate cereals in rainfed environments II. Phasic development and growth

Barley yields more grain and total biomass than does triticale which in turn yields more biomass than do bread wheat, durum wheat and oats when sown at the same time in rainfed environments in southern Australia. To determine reasons for these differences, cultivars of each species were grown at five field sites and variation in their phenology and both pre- and post-anthesis growth was measured. Barley achieved a higher yield of grain and biomass in a shorter duration than the other species. It reached physiological maturity about 10 days (180 thermal units) before the other species, and reached double ridge and anthesis earlier. Triticale was also earlier to reach double ridge and terminal spikelet than the mean for the other species, although it had a similar physiological maturity to the wheats. Barley and triticale developed a greater leaf area and dry mass faster than the wheats and oats. The differences in leaf area was established from the time the first leaf had fully expanded. Barley also developed mainstem leaves and tillers faster than the other species whereas triticale was slower in this respect. Crop growth rate was greatest in barley and triticale up to anthesis, but no differences between species were found in their relative growth rates. The growth rate of individual grains and of total grain per unit ground area were substantially greater in barley than the other species. Oats and durum wheat had the slowest individual grain and total grain growth rates. Grain growth rate per unit ground area was significantly associated with grain yield at one site where this was examined. The change in stem mass between anthesis and physiological maturity, which was determined to assess the possible contribution of stem reserves to grain, was also positively associated with grain yield at the two sites where it was determined, and more so at the drier site. The change in stem mass averaged 76 g m −2 at the two sites and this represented 25% of the total grain yield. However, the range varied from 13 to 39% of grain yield (corrected for husk mass in barley and oats). The loss in leaf sheath mass averaged 68 g m −2 at both sites; this was not associated with grain yield.

Responses of spring wheat exposed to pre-anthesis water stress

Spring wheat cv. Yecora 70 was exposed to soil water deficits during three phases between emergence and anthesis: early (22 days after sowing to terminal spikelet), mid (terminal spikelet to anthesis) and late (early boot to anthesis). The objective was to quantify the effects of water stress on partitioning of above-ground biomass to the spike, the ratio between kernel number and anthesis spike weight, canopy expansion, radiation interception and phenology. This information can be used to test the assumptions used when modelling wheat growth and yield under water-limiting conditions. The extension rate of the lamina and pseudostem was reduced when more than 50% of the extractable soil water had been extracted from the root-zone, independent of the stage when stress was imposed. Stress reduced biomass accumulation more through a reduction of the amount of radiation intercepted than reduced radiation-use efficiency. The reduction in the amount of radiation intercepted was due to lower leaf area index, as the radiation extinction coefficient was similar under stress and non-stress conditions. Stress treatments reduced spike biomass at anthesis to 58-94% of that in the well-watered control, but had little effect on the pattern of biomass partitioning to the spike and the proportion of anthesis biomass as spike. Stress after terminal spikelet reduced the ratio of kernel number to anthesis spike weight by 50%, suggesting that reduced kernel number under stress may not be solely due to a restricted assimilate supply. This study showed that current assumptions are valid regarding the response of wheat to pre-anthesis stress in terms of canopy expansion, radiation interception and biomass partitioning to the spike. However, the constancy of the ratio of kernel number to anthesis spike weight was shown not to hold under water stress.

Time of Salt Stress Affects Growth and Yield Components of Irrigated Wheat

AbstractSalt tolerance of wheat (Triticum aestivum L.) is known to change during different stages of growth. The effects of salinity on growth and yield components of wheat at different stages of growth were determined in a 2‐yr field plot study at Brawley, CA. Four salinity levels were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl2(1:1 w/w). Electrical conductivities of the irrigation waters were 1.4, 10.0, 20.0, and 30.0 dS m−1 in 1989, and 1.4, 8.0, 16.0, and 24.0 dS m−1 in 1990. The three irrigation treatments were (i) salinity imposed throughout the growing season, (ii) saline irrigation initiated after terminal spikelet differentiation (TSD), and (iii) saline irrigation discontinued at TSD. Growth and yield components measured were straw yield, total above ground biomass, number of spikelets per spike, number of kernels per spike, individual kernel weight, number of tillers per plant, and number of tiller spikes. Continuous salinity throughout the growing season significantly reduced all growth and yield components. Salinity imposed prior to TSD reduced the number of spikelets per spike and the number of tillers per plant, whereas salinity imposed after TSD significantly reduced only kernel number and weight. In general, the effect of salinity appears to be most pronounced on the yield components that are growing or developing at the time the salt stress is imposed. Total grain yields were maintained when moderately saline irrigation waters were substituted for good quality water during part of the growing season.

Sensitivity analyses of the ARCWHEAT1 crop model: the effect of changes in radiation and temperature

SUMMARYThe sensitivity of predicted final grain yield to changes in the mean and variance of daily temperature and daily log(radiation) was studied for the arcwheat1 crop model of winter wheat. These two climatic variables were each simulated by each of two stochastic models, the parameters of which were estimated from 12 years' data from Rothamsted Experimental Station.When arcwheat1 was run with systematic changes in daily temperature from – 2 °C to +2 °C in steps of 0·1 °C, there were abrupt changes in predicted final grain yield which coincided with predicted increases in leaf number. These effects were smoothed out when the stochastic climate models incorporating simulated daily variation were used as inputs, in multiple runs of arcwheat1.In such runs, the response of predicted yield to changes in the means of temperature and log(radiation) was studied both for individual developmental stages and over the entire growing season. Yield was insensitive to changes in temperature and radiation during the stage between sowing and emergence, and to changes in radiation before terminal spikelet formation.

Simulation models for strategic and tactical management of crops and pastures

Australian crops and pastures are grown in climates which are relatively variable at present and may become more variable if the. global climate changes. Optimal management in relation to this variability has two strands. The best-bet management strategy must be identified for the long-term climate and modified with any climate change. Variation in weather between years, however, is already greater than changes in the mean expected from climate change, so improved management tactics to cope with current variability will lead to systems with long-term resilience.Examples using the SIMTAG and maNage models are described for improved strategic and tactical management of rainfed wheat. SIMTAG is used to clarify the extent to which regional yields are currently limited by weather and to make a strategic assessment of optimal sowing date. The maNage model is used for tactical management of supplementary N fertiliser for dryland wheat. maNage shows that the reliability of yield response is increased if the N is applied at the terminal spikelet stage but only if the amount of stored soil water is above a defined threshold.Future integration of crop models with pasture models is discussed. Pastures make up the largest landuse on farms in the region. They have special importance because they influence the growth of crops grown in sequence. Modelling the interaction of pastures-crop sequences and crop-crop sequences in relation to weather is important for increasing yields of both crops and pastures.

Growth and Development of Uniculm and Conventional‐Tillering Barley Lines

AbstractBarley (Hordeum vulgare L.) producers in northern regions require genotypes that develop and mature rapidly. Although the phenological development of barley has been studied extensively, the effect of the uniculm character on rate of growth and development has not been investigated. The objective of this study was to compare the growth and development of uniculm and conventional‐tillering near‐isogenic barley lines. Three pairs of near‐isogenic lines that differed by the presence of the uc2 (uniculm) gene were evaluated at Palmer and Fairbanks, AK during the 1990 and 1991 growing seasons. Averaged over four environments, uniculm genotypes required more growing degree days (GDD) to reach double ridge formation, but there were no differences for GDD to terminal spikelet formation (P < 0.01). Uniculm genotypes had 0.3 more leaves per main culm, required 12 fewer GDD to reach full flag leaf extension, and had a leaf appearance rate that was 0.12 leaves (100 GDD)−1 faster than conventional genotypes (P < 0.01). Uniculm genotypes matured 23 GDD earlier and were 10.9 cm taller than their conventional counterparts (P < 0.01). The restriction of a single culm per plant decreased kernels per spike by 2.2 kernels and increased kernel weight by 8.4 mg (P < 0.01). Our results suggest that the uniculm phenotype results in several favorable modifications of phenological development, which may be of practical value in regions where early maturity is important.

Leaf Emergence, Tiller Growth, and Apical Development of Nitrogen‐Dificient Spring Wheat

Conflicting reports exist about the effect of N supply on the rate of leaf emergence. We examined effects of N deficiency on leaf and tiller emergence, tiller initiation and apical development in ‘Aroona’ and ‘Gamenya’ spring wheat (Triticum aestivum L.). Four levels of N (e.g., 50 μM N = N50) were supplied by hourly irrigation with complete nutrient solution of plants growing in sand. The control plants in Exp. 1 (N1600) had 64 g kg‐1 N intheshoots at the two‐leaf stag e, compared with 33 in N50, 50 in N300, and 58 in N800. Compared with control plants, dry matter of N50 plants was 10%, N300 50%, and N800 80%. Results in Exp. 2 were similar. The rate of leaf emergence was decreased in all N50‐treated and some N200‐treated plants, but not or N300‐treated plants. Tiller bud initiation was decreased in the treatment. The number of tiller buds was correlated with total number of leaves; if a leaf emerged, N deficiency did not affect tiller initiation. Nitrogen treatment did not alter the sequence of tiller emergence, but tiller emergence was delayed or did not occur in N50, N200, and N300 plants. Nitrogen treatment had little effect on the rate of apical development. The double‐ridge stage of development was delayed ≈2 d for both cultivars at the two lowest N treatments. Terminal spikelet production was also delayed by ≈2 d at these N treatments in Aroona, but not in Gamenya spring wheat. The rate of primordia initiation was decreased in N50 and N300 plants, resulting in fewer spikelet primordia. The level of N deficiency affected plant response to the stress.

Effect of temperature, vernalization and water stress on phyllochron and final main-stem leaf number of HY320 and Neepawa spring wheats

An understanding of the effect of environment on leaf growth is needed to accurately simulate phenological development of a cereal crop. This study was conducted to determine the effect of temperature, cold (vernalization) and water stress on the phyllochron (degree-days leaf−1) prior to the terminal spikelet stage and on the final leaf number produced by the main stem (FLN) of two spring wheat varieties (Triticum aestivum L.), Neepawa and HY320, grown on the Canadian prairies. Within each of five day/night temperature regimes (30/25 °C, 24/19 °C, 21/12 °C, 16/7 °C and 7/2 °C, with means of 28 °C, 22 °C, 18 °C, 13 °C and 5 °C, respectively), the varieties were grown under two cold (not vernalized and vernalized) and two water (wet and dry) treatments. Within a given temperature regime, both varieties responded similarly to the cold treatments. Vernalization reduced phyllochron and FLN in all but the lowest temperature regime, where phyllochron increased and FLN was unaffected. When effective, severe water stress increased phyllochron and decreased FLN. HY320 was relatively more affected by vernalization and less affected by severe water stress than Neepawa. For both varieties, phyllochron was curvilinearly related to temperature and increased as temperature increased. The relationships were noticeably altered by vernalization and severe water stress. When not vernalized, FLN for HY320 increased as temperature increased; FLN for Neepawa reached a maximum at 20 °C. When vernalized, FLN was independent of temperature under optimum water; the reduction of FLN by severe water stress increased as temperature increased. The results of this study suggest that the effect of environmental change on both phyllochron and FLN must be accounted for when accurate and reliable modelling of the early development of spring wheat is required.Key words: Spring wheat, phyllochron, leaf number, temperature, water stress, vernalization