Variation In Number Of Grains Research Articles

Associations between endogenous spike cytokinins and grain-number traits in spring wheat genotypes

Genetic variation in grain number has been positively associated with levels of cytokinins in inflorescences in cereals, although studies quantifying endogenous levels in the field are currently lacking. The present study, using a spring wheat association mapping panel (HiBAP II) of 150 lines, quantified associations between spike hormone levels and grain number and associated traits. The HiBAP II panel was grown in the field in NW Mexico under irrigated conditions for one year and a subset of ten genotypes in the glasshouse under well-watered conditions for three years. The spike levels of four cytokinins (trans-zeatin riboside, trans-zeatin, isopentenyladenosine, and isopentenyladenine) were measured by using ultra-high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. In the glasshouse experiments, spike hormone levels were measured at booting and anthesis, and in the field experiment at anthesis. In the glasshouse experiments, cytokinin levels were also measured in the basal, central, and apical spikelets separately in addition to at the whole spike level. The spike cytokinin levels did not differ significantly between the basal, central and apical sections of the spike. or show a spike position × genotype interaction. In the glasshouse experiments, significant genetic variation was detected for the expression of the four cytokinins in spikes at booting. At booting, spike trans-zeatin concentration ranged amongst genotypes from 4.5 to 16.0 ng g−1 FW and was positively correlated with grain number per main shoot (r = 0.77, P < 0.05). In the field at anthesis, the spike levels of each of trans-zeatin, trans-zeatin riboside and isopentenyl adenosine were positively correlated with grains per m2 (r = 0.17–0.19, P < 0.05). Our results indicated that selection for high spike cytokinin levels in wheat germplasm offers scope to raise grain number and yield potential in wheat.

High responsiveness of maize grain yield to nitrogen supply is explained by high ear growth rate and efficient ear nitrogen allocation

Increasing the response of maize yield to nitrogen (N) application is essential for food security and economic benefits of the farmers. However, the physiological mechanism underlining N responsiveness is unclear. Three maize cultivars with different N-responsiveness, BMY (the low), ZD2 (the medium) and ZD958 (the high) were grown in the field under a wide range of N supply (from 0 to 240 kg N per ha) in two years. Plant growth rate, plant N uptake rate, ear growth rate and ear N allocation rate, and their relationship to grain yield formation were investigated during the early critical period (14 days before silking). The direct path coefficient of grain number to grain yield was 0.82, which explained 96% of the variation in grain yield (R 2 = 0.91). There was not a trade-off between grain number and other yield components. ZD958 got more grains per ear than the other cultivars in response to N supplies. The variation in grain number was mostly explained by the number of floret primordia (57% for BMY, 93% for ZD2 and ZD958). When N supply increased from 0 to 240 kg N ha -1 , ZD2 and ZD958 did not differ in nitrogen nutrition index, and were 7.2–32.8% higher than BMY. The number of grains and floret primordia was independent of plant growth rate and plant N uptake rate, although these rates increased with N supply. Ear growth rate and ear N allocation rate of ZD958 were higher compared with the other cultivars, especially under high N supply. Except BMY, the number of floret primordium and grain per ear depended on ear growth rate and ear N allocation rate. There was a positive correlation between ear growth rate and ear N allocation rate in ZD2 and ZD958. However, ear N allocation rate of BMY did not increase when its ear growth rate was greater than 19.2 mg o C -1 . It is concluded that, with increasing N supply, N-responsive maize cultivars had high ear growth rate and allocated more N into the ear during the early critical period, which enhanced the differentiation of floret primordia, hence increasing grain number and final grain yield. • High N-responsiveness of grain yield depends on grain number per ear. • Genotypic variation in grains number is explained by floret primordium development. • Floret primordium number in response to N depends on ear growth and ear N allocation.

Wheat grain number and yield: The relative importance of physiological traits and source-sink balance in southern Australia

Grain number (GN) is determined by spike growth rate (SGR), fruiting efficiency (FE) and the duration of spike growth period (Ds). However, these three traits are not independent of each other and therefore quantifying their relative contribution to GN is important for improving yield potential. This study aimed to model GN as a function of SGR, FE and Ds in bread wheat and investigate the relative importance of these three traits in determining GN. A large number of commercial varieties, elite wheat breeding lines, and a Multiparent Advanced Generation InterCross population were evaluated for GN, SGR, Ds, and FE in six Australian environments in 2014 and 2015. The model explained 43–98% of the variation in GN in individual environments and 88% of the variation in GN across the six environments. The percentage of GN variance explained by the model was significantly higher than those explained by correlating GN to individual traits. The relative importance of the contribution of the three traits to GN was different and ranked as SGR > FE > Ds. The negative correlation between FE and spike dry weight at anthesis (SDWa) appears to be spurious, suggesting that there was no causality between high FE and low SDWa and vice versa. Thus, FE can be used as an independent trait to increase GN in addition to SGR and Ds. We also investigated if the wheat crop had enough source to fill the increased sink size in the southern Australian high rainfall environment. The source-sink balance analysis indicates that the available source, consisting of concurrent photosynthetic assimilate and stored water-soluble carbohydrate at anthesis, was sufficient to fill the established sink but no surplus assimilates were available to fill a larger sink in southwestern Australia. However, the opportunity to increase yield potential by further increasing grain number might exist in south-eastern Australia environments.

Grain yield and grain protein of old and modern durum wheat cultivars grown under different cropping systems

A five-year field trial was performed in a typical Mediterranean environment to compare grain yield (GY) and GY stability, grain protein percentage (GP) and GP stability resulting from different cropping systems: two based on 14 old durum wheat landraces/cultivars grown in low-fertility soils; and one based on 14 modern cultivars grown in high-fertility soils. Cropping systems were also differentiated in terms of sowing date, sowing rate (250 vs. 350 viable seeds m−2 for the modern cultivars only) and nitrogen rate (36, 76 and 112 kg N ha-1 on average for the ‘OLDlow’, ‘OLDmedium’ and ‘MODERN’ cropping systems, respectively). Depending on the year, the GY of the OLDlow system ranged from 22% (2017) to 74% (2016) of that obtained in the MODERN system. The maximum GY obtained in the OLDlow system was 4.18 t ha-1. The average GY obtained with modern cultivars varied from 5.6 to 6.6 t ha-1; with the exception of that obtained in 2016 (only 3.37 t ha-1). The higher GY of the modern cultivars was the main cause of higher rainfall productivity, reaching a maximum value of 23 kg ha-1 mm-1. In all the systems, the between-year variation in GY was associated with the corresponding variation in grain number m−2 (GNO), but anthesis date was only negatively associated with GY for the old cultivars, while GP was negatively associated with GY and GNO only in the modern cultivars. GP was always higher in the OLDlow (11.9–14.0 %) and OLDmedium (13.4–15.7%) systems compared with the MODERN one (10.5–12.1 %) in spite of the lower nitrogen fertilization rate, which also assured a higher nitrogen fertilizer recovery efficiency.The three systems were comparable in terms of GY stability, in spite of the later anthesis of old cultivars, which was expected to exacerbate the impact of the terminal drought typical of Mediterranean environments. With regard to GP stability, the old cultivars were less stable than the modern ones. The greatest GxY interaction was generated by the more favourable years, whereas the least interaction occurred in the year with the most severe drought stress. Rainfall, during post-anthesis in particular, but also after sowing, was the main driver of GxY interaction for GY and GP, either directly or via its interaction with nitrogen availability.

The impact of variation in grain number and individual grain weight on winter wheat yield in the high yield potential environment of Ireland

Abstract Previous studies from regions that produce high proportions of global winter wheat have highlighted that difference in sink size influences the majority of variations in winter wheat yield. However, the potential for source limitation due to environmental differences in regions that consistently produce a large sink capacity (i.e. >20,000 grains/m2), such as Ireland, have not been widely studied. The aim of this study was to characterise the variation in growth pattern and yield components that contribute to variations in grain yield in regions of high yield potential, and to identify the periods of development that are most likely to influence yield in these regions. Monitor crops of winter wheat were grown at three sites with contrasting latitudes on the island of Ireland, during three growing seasons (2013–2015). Crops were assessed regularly for measurements of crop growth and development, including biomass accumulation, canopy development and light interception. Grain yield ranged between 10.7–15.8 t/ha at 15% moisture content, with a grand mean of 12.7 t/ha. Results indicated that variations in grains/m2 had a larger effect on winter wheat yield than variations in individual grain weight. Variability in grains/m2 was influenced by changes in spikes/m2 more than the number of grains/spike. While spikes/m2 at harvest was significantly related to the number of shoots/m2 at GS59, no significant relationship was observed between the shoots/m2 at the time of maximum tillers/plant and spikes/m2 at harvest. Furthermore, a significantly negative linear relationship was observed between shoots/m2 at the time of maximum tillers/plant and grains/spike. Therefore, high rates of tillering were not beneficial to yield formation in the majority of crops monitored. A strong effect of individual grain weight was observed at one site of the nine evaluated in the study, indicating that a partial source limitation of yield is possible in certain Irish environmental conditions. However, variations in grain yield of crops of winter wheat grown at different locations in Ireland in different seasons were primarily driven by variations in grain number, and therefore were generally sink-limited.

Genetic variation for wheat spike fertility in cultivars and early breeding materials

SUMMARYGrain yield in bread wheat is often tightly associated with grain number/m2. In turn, spike fertility (SF), i.e., the quotient between grain number and spike chaff dry weight, accounts for a great proportion of the variation in grain number among cultivars. In order to examine the potential use of SF as a breeding target, (1) variation for the trait was assessed in six datasets combining commercial cultivars under different environmental conditions, (2) trait heritability was estimated in a set ofF1hybrids derived from controlled crosses between cultivars with contrasting SF and (3) SF distribution pattern was analysed in twoF2segregating populations. Analysis of commercial cultivars revealed considerable variation for SF, under both optimal and sub-optimal conditions. In addition, genotypic variation was consistently larger than genotype × environment interaction variation in all datasets. Narrow sense heritability, estimated by the mid-parent-offspring regression of 20F1hybrids and their respective parents, was 0·63. Data from twoF2populations exhibited bell-shaped and symmetric frequency distributions of SF, with a SF mean intermediate between the parental values. Substantial transgressive segregation was detected in bothF2populations. In conclusion, SF appears to be a heritable trait with predominantly additive effects. This warrants further investigation on the feasibility of using SF as an early selection criterion in wheat breeding programs aimed at increasing grain yield.

Fine mapping a domestication-related QTL for spike-related traits in a synthetic wheat

QTL analysis using a BC5F2:3 mapping population derived from a cross between Am3, a synthetic hexaploid wheat as a donor parent, and Laizhou953, a Chinese winter wheat cultivar as a recurrent parent, showed that variation at the microsatellite locus Xgwm113 on chromosome 4B was associated with variation in grain number per spike (GN), spike length (SL), and spikelet number per spike (SPI). The Qgn.caas-4B, Qsl.caas-4B, and Qspi.caas-4B were responsible for 16.6%-35.6%, 18.0%-32.3%, and 23.7%-25.9% of the phenotypic variation present in two environments, respectively. Segregation for GN fit a Mendelian monogenic ratio. A subpopulation consisting of 497 plants was used to map the QTL to a 1.2cM interval between Xgwm113 and Xgwm857. The three spike traits, GN, SL, and SPI, were correlated and were thus probably under the pleiotropic control of the QTL. The Am3 allele had a reduction effect on all three spike traits. Evidence for positive selective history on SSR locus Xgwm113 was supported using Ewens-Watterson's statistic test on a germplasm panel of wild and landrace entries, suggesting that this genomic region may contain genes under selection during wheat domestication.

Constitutive modelling of microstructured components fabricated by micro powder injection molding

A constitutive model based on Besson and Abouaf’s constitutive equation was established to simulate densification of 316L stainless steel microstructured components fabricated by micro powder injection molding. A new sintering stress expression for final stage sintering was established by including the variation in grain number during grain growth. Different diffusional creep, sintering stress and internal gas pressure were assumed for the substructure, in the millimeter regime, and the microsize structures, respectively. The predictive capability of the model was verified by comparing the theoretical calculations with the experimental results. The calculations agreed reasonably well with the experimental results. Neglecting the variation in grain number in the sintering stress was found to yield lower predicted densities of the microsize structures.

Genetic variation in grain-filling ability in dwarf pearl millet [Pennisetum glaucum (L.) R. Br.] restorer lines

The d2 dwarfing gene in pearl millet [Pennisetum glaucum (L.) R. Br.] carries a yield penalty due to an associated reduction in individual grain mass. This reduction, however, varies with genetic background, indicating that it may be possible to select against poor grain filling in d2 dwarfbackgrounds, given an effective measure of grain filling. This study was conducted to assess genetic variability forgrain-filling ability (in contrast to simply grain size),and its relationship to grain yield,indwarf pearl milletrestorer (R) lines. The grain-filling ability (GFA) of an individual R line was defined as the least squares estimate of its effect on individual grain mass in the analysis of variance, following a linear covariance adjustment for grain number. The study was based on 93dwarf hybrids involving31 d2 dwarfR-lines, evaluated over 3 years. Half of the variation in individual grain mass in the 93 hybrids was related to variation in grain number. Covariance adjustment in individual grain mass for grain number resulted in highly significant differences among hybrids and R lines in GFA. The R-line combining ability for GFA accounted for 26% of the variation in the R-line combining ability for yield, compared to 46% for the combining ability for grain number, and just 8% for the combining ability of individual grain mass. The combining ability for GFA was independent of the combining ability for various pre-flowering effects, including grain number, but was related to the combining ability for individual grain mass and harvest index. Improvement in individual grain mass achieved through selection for GFA should translate directly into yield improvement, whereasimprovement by direct selectionfor individual grain mass is less-likely to do so.

On-farm assessment of regional and seasonal variation in sunflower yield in Argentina

Using an on-farm approach, we investigated constraints to actual yield of sunflower in six agroecological zones within the Argentine Pampas during three growing seasons. In 249 large, grower-managed paddocks, we quantified a series of variables related to: (1) crop phenology, growth, and yield; (2) the physical and biological environment; and (3) management practices. Variation in yield among zones and seasons was analysed on the basis of four biologically-founded assumptions: (1) grain number accounts for a large proportion of the variation in yield; (2) grain number is associated with a photothermal coefficient, Q= R ( T- T b) −1, where R and T are average solar radiation and air temperature respectively, during the 50-day period bracketing anthesis; and T b is a base temperature; (3) crop growth and yield are proportional to light interception, and therefore proportional to canopy ground cover; and (4) yield is proportional to the fraction of seasonal rainfall that occurs after anthesis. Average yield ranged from 1.1 to 2.7 t ha −1, grain number from 2400 to 5400 m −2, individual grain mass between 40 and 69 mg and grain oil concentration between 42 and 52%. Grain number accounted for 43% of the variation in average yield while Q accounted for 23% of the variation in grain number. Low yield was associated with deficient ground cover in 25% of the crops; part of the remaining variation in yield was accounted for by sets of measured variables particular to each zone, including soil shallowness, low available P, low initial water content, weeds and diseases — chiefly Verticillium wilt ( Verticillium dahliae) and Sclerotinia head rot ( Sclerotinia sclerotiorum). Across zones and seasons, the proportion of seasonal rainfall occurring after anthesis accounted for 28% of the variation in crop yield. A trade-off is highlighted whereby beneficial effects of rainfall that favours growth and yield may be offset by the detrimental effect of abundant moisture that favours major fungal diseases. We emphasised the value of combining experimental studies — which provide biological background in the form of working hypotheses — with on-farm research that realistically quantifies yield response to key factors.

Grain yield in wheat: Effects of radiation during spike growth period

The effect of radiation on yield formation in irrigated and fertilized spring wheat was quantified, focusing on the crop growth and partitioning during the spike growth period, critical for the determination of number of grains. Most of the data were obtained from five experiments at Balcarce, Argentina, with cv. PROINTA Oasis. Additional data were obtained from an experiment in Sonora, Mexico. A wide range of incident radiation during spike growth was achieved, both by natural variation among experiments and by applying shading nets. Spike growth period was defined as the interval during which spikes achieved from 5% to 100% of the dry weight they accumulated by day 7 after anthesis excluding grain weight. Radiation level during this period affected yield mainly through variation in number of grains m −2. Differences in grains m −2 were related to differences in dry weight of spikes m −2 measured 7 days after anthesis excluding grain weight. Above 106 g m −2 of spikes, the relationship between grains m −2 and dry weight of spikes m −2 was approximately linear with positive slope and intercept. The slope obtained at Balcarce (58 grains g −1 spike) was not different from those obtained in Sonora (58–62). For low weight of spikes (< 106 g m −2), the slope increased and the intercept decreased. Thus, the relationship was not linear and the number of grains g −1 spike was not constant, reaching its maximum value at 106 g m −2 of spikes. The cause of the variation in number of grains g −1 spike due to radiation does not seem to operate through a change in spike rachis proportion. Nevertheless, variation in radiation level caused greater variation in dry weight of spikes m −2 than in number of grains g −1 spike. For Oasis at Balcarce, the duration of the spike growth period (27 days) was steady between shading levels and experiments. Thus, the smaller dry weight of spikes m −2 induced by low radiation was due mainly to the lower spike growth rate. Crop and spike growth rate were positively related although low radiation increased mean and maximum partition to spikes. Crop growth rates, during the spike growth period, was linearly related to intercepted PAR (photosynthetically active radiation), and radiation-use efficiency was little affected by radiation level. Shading increased green area ratio (i.e., the ratio of green area index to crop dry weight) but it slightly affected green area index and extinction coefficient. Therefore, the percentage of intercepted PAR was not affected by radiation level. Intercepted radiation was the main factor determining both crop and spikes growth during spike growth period, and grain number m −2 was linearly related to accumulated intercepted PAR during this period.

Effects of Radiation and Temperature on Tiller Survival, Grain Number and Grain Yield in Winter Wheat

Effects of the environment on shoot survival were studied in winter wheat cv. Avalon grown in microplots at a density of 247 plants m−2. The incident radiation and mean temperature were altered during one of three periods of between 14 and 29 d duration, the first (P1) starting at the end of tiller production and the last (P3) finishing near the end of the tiller death phase, about three weeks before anthesis. Plants were given temperature and radiation treatments in growth rooms in two experiments and extra light outdoors in a third experiment: they were at other times grown outdoors. Increasing radiation by between 60 and 100 per cent during P1 had negligible effects on shoot number; during P2 it always delayed tiller death but increased final ear number in only one experiment; during P3 it consistently increased ear number by up to 100 m−2. Increased radiation always increased crop dry weight immediately after treatment but only sometimes did this increase persist to maturity. Grain dry weight was increased by treatment during P3 of one experiment. Increasing the temperature by 4 °C decreased shoot number, usually only temporarily, by hastening death of some tillers. Warmer temperatures decreased crop growth after, but not during, treatment and decreased grain dry weight. Radiation and temperature rarely interacted. Variation in grain yield within and between experiments related well to variation in number of grains m−2, which in turn related to variation in ear dry weight at anthesis.

Relationships between grain yield and morphological characters in the winter wheat genotypes of the Belgian national list

Yield per shoot and to a much lesser extend yield per unit area were related to morphological characters. The flag sheath was better related to shoot yield than were any of the three uppermost leaf laminae. Among these the areas of the two lower leaves showed a better relationship to the yield than did the flag leaf lamina. Variation in main shoot yield was associated mainly with variation in grain number. More attention should be given to morphological character related to spike development before anthesis.

Temperature effects at three development stages on the yield of the wheat ear

Temperature effects on the growth and yield of wheat (cv. Gamenya) were studied in controlled environments under three day/night temperature regimes (viz. 25/20, 20/15 and 15/10°C) and at three stages of development, viz. vegetative, ear development and grain growth stages. The most important temperature effects were found during the ear development phase. Plants grown at low temperature at this time had long culms, large flag leaves and more potentially fertile florets in each spikelet. The number of florets which produced harvestable grains, and the weight of these grains at maturity, were affected by temperature during the grain growth stage. Temperature prior to floral initiation was not of major importance to final ear weight in this variety, but it did have an effect on the number of mature ears present at harvest. Grain weight per ear at maturity was found to be highly correlated with the number of grains set (r = 0.96), and hence variation in grain number accounted for most of the variation in ear grain weight. In those treatments where grain numbers were not markedly depressed by the temperature treatments, a hlgh positive correlation was found between flag leaf area duration and total grain yield (r = 0.73).

Investigations on the physiology of yield in winter wheat, by comparisons of varieties and by artificial variation in grain number per ear

Elliott (1962) estimated that the average grain yield of wheat in the United Kingdom increased by 6·1 cwt per acre between 1947 and 1957. By considering results of yield trials carried out by the National Institute of Agricultural Botany he attributed 3·8 cwt of this increase to greater yielding ability of new varieties and the remainder to ‘other factors’, including the increased use of fertilizers, chemical weed control, better seed dressings and combine harvesters. The genetic improvement obtained by breeding new varieties is due partly to the incorporation of characters which are comparatively easily recognized, such as resistance to various diseases and lodging. However, even when these major limiting factors are absent from the environment the new varieties give higher yields, presumably due to physiological superiority. Many investigations, reviewed by Thome (1966), have sought to identify and establish the relative importance of the responsible physiological characters, but the information is still far from complete. This shortcoming is now the chief hindrance to more efficient choice of varieties for use as parents and selection of improved genotypes by the breeder. The objective of the three experiments reported here was to provide further information on the physiological basis of varietal differences in yield in wheat.

Yield characters of selected oat varieties in relation to cereal breeding technique

1. Results obtained from two seasons' population studies of selected spring oat varieties in Scotland indicated that extent of tillering had little or no effect on yield. These results are in sharp contrast with those obtained by workers with wheat.2. The yield of individual plants under the conditions of the experiments became adjusted to differences in population density primarily by variation in number of grains per panicle. Spikelet weight tended to be negatively correlated both with population density (external competition) and with number of grains per panicle (intrapanicle competition). These factors tended to neutralize each other.3. The decrease in size of additional grains in spikelets with more than one grain was balanced by increased weight of the basal grains as compared with the weight of a single grained spikelet. Average grain weight per spikelet therefore tends to remain constant.