Kernel Growth Rate Research Articles

Flame kernel evolution and shock wave propagation with laser ignition in ethanol-air mixtures

Flame kernel evolution and shock wave propagation in ethanol/air mixtures with laser ignition in a constant-volume chamber was investigated by means of high-speed Schlieren photography. At initial pressure of 0.1 MPa and temperature of 333 K, ignition was performed using a pulsed laser at the second harmonic wavelength with six different laser energies from 75 to 200 mJ, for the equivalence ratios ranging from 0.8 to 1.4. A cross-shaped plasma spot is captured ∼3.0 µs after the laser triggering, whereas the shape of the flame kernel is initially circular and then transforms to an ellipsoid structure. Following the contraction of the plasma, the flame kernel growth rate is initially very different in the four directions and then approaches a steady flame speed. The contraction of the plasma zone is accompanied by a rapid shock wave propagation where, the wave propagation speed is found to be negligibly influenced by the variations in either laser energy or mixture equivalence ratio. Under the test conditions in this study for ethanol/air mixtures, the initial shock wave speed is ∼480 m/s which decays to ∼380 m/s after 20 µs. The shock wave front propagates with a time dependency of about t0.6 when t < 20 µs, and then it becomes an approximately linear function of time.

The effect of nanosecond pulsed high frequency discharges on the temperature evolution of ignition kernels

Nanosecond pulsed high frequency discharges (NPHFD) have attracted interest as a means of enhancing ignition probability and ignition kernel growth rates. Previous studies have shown that increasing the pulse repetition frequency (PRF) of a NPHFD burst can result in enhanced probability of ignition relative to lower values of PRF. The cause of this enhanced ignition probability is not well understood, in part, because the temperature evolution of ignition kernels have not been measured. In this work, an inverse deconvolution technique was developed, evaluated, and used to determine the temporal evolution of the temperature and volume of ignition kernels initiated by NPHFD and single pulse discharges. Radiation intensity measurements of ignition kernels were compared to modeled values to determine path-averaged temperatures. Comparisons of values derived using the deconvolution technique and measured temperatures above a McKenna burner typically agreed within 4%. When the technique was applied to ignition kernels initiated by NPHFD over a range of PRF, it was observed that increasing the PRF of a discharge sequence increased the initial rate of change of the temperature as compared to lower PRF. Additionally, kernels generated with high PRF discharges achieved higher initial peak temperatures than those generated by lower PRF discharges. A relaxation in temperature was observed following the peak, which was followed by a subsequent temperature increase in all cases generated with PRF > 10 kHz. PRF above 5 kHz result in larger initial kernel volumes and volume rates of change compared to those observed for lower PRF values. This is attributed to pulse-to-pulse coupling during the energy deposition process. The observed relationship between kernel temperature, volume, and PRF help to explain ignition probability measurements reported previously. Findings from the effort illustrate how the rate of energy deposition through pulse-to-pulse coupling can significantly enhance ignition through elevated temperatures.

Reduction of flame development time in nanosecond pulsed high frequency discharge ignition of flowing mixtures

The effects of discharge and flow parameters on ignition kernel development time are explored in flowing methane–air mixtures. A nanosecond pulsed high frequency discharge in a pin-to-pin configuration is used as the ignition source, providing 2.9 ± 0.23 mJ/pulse. The effects of pulse repetition frequency (PRF) in the range of 10–300 kHz, number of pulses in the range of 1–50 (≈2.9–145 mJ), equivalence ratio in the range of 0.55–0.65, gap distance in the range of 0.5–2.5 mm, and flow velocity in the range of 2.5–10 m/s are explored. For all conditions, the ignition events are in the “fully-coupled” regime, in which high ignition probability is achieved and locally extinguished ignition kernels are avoided. It is found that reducing the PRF reduces the kernel development time for fixed total energy deposition due to an increased volume of unburned mixture exposed to the discharge. Increasing the number of pulses at a given PRF also decreases the kernel development time, again by increasing the volume of gas exposed to the discharge. The equivalence ratio only has an effect on the kernel growth rate after the discharge, with identical kernel areas measured at all equivalence ratios while the discharge is active. Increasing gap distance decreases the kernel development time by providing a larger initial kernel volume as well as reducing heat and radical quenching at the electrode surfaces. Finally, the flow velocity has an effect on the kernel growth rate at velocities greater than 5 m/s, with larger flow velocities resulting in shorter kernel development time. This is due to the competing rates of self-propagating flame expansion and kernel growth due to convection past the discharge region. The combined effects of all of the above parameters on the kernel area after the discharge are summarized in a correlation equation, which predicts the trends in kernel growth rate based on an estimated plasma area defined by the discharge duration, flow velocity, and gap distance.

Comparative kernel growth and yield components of two- and six-row barley (Hordeum vulgare) under terminal drought simulated by defoliation

Barley (Hordeum vulgare L.) is often grown in sites with low rainfall and high temperature during grain filling. Because spike architecture is one of basic footprints of barley domestication, the importance of spikes in adaptation to different environments or abiotic stresses can be hypothesised. In order to compare different barley spike types in terms of kernel growth and yield components, we tested 15 two-row and 10 six-row winter genotypes in eight environments where terminal drought was simulated by defoliation at 7 days after heading (7 DAH). Control plants were grown intact. On average, two-row genotypes outyielded six-row genotypes by 17% under control conditions and 33% under simulated late drought. Observations of kernel dry weights from 7 DAH through to harvest maturity at 5-day intervals were regressed onto a measure of thermal time. After preliminary evaluation of four nonlinear (S-shaped) models for kernel dry-weight accumulation, the ordinary logistic model was deemed the most appropriate in most cases and was finally applied to all plant-growth curves. Four parameters were estimated from the logistic model. Whereas two earliness estimators (inflection point and thermal time needed to reach maximum kernel weight) were similar for the two barley types, maximum kernel weight (Ymax) and mean rate of kernel growth (RG) were higher (P&amp;lt;0.05) in two-row than in six-row barleys. Differences in Ymax and RG among six-row barley genotypes were greater between control and defoliation treatments than between years, whereas among two-row barley genotypes, differences between years were greater, suggesting better stability of six-row types and better drought tolerance of two-row types in the tested barley set.

Temporal evolution of auto-ignition of ethylene and methane jets propagating into a turbulent hot air co-flow vitiated with NOx

In this paper, the temporal evolution of auto-ignition (AI) of C2H4 and CH4 jets propagating into a NOx vitiated hot co-flow at high velocity and turbulence was studied. Simultaneous temporally-resolved planar laser-induced fluorescence (PLIF) experiments of OH and CH2O were carried out in a recently developed test rig for auto-ignition studies of turbulent non-premixed flows. Flame stabilization mechanisms were analyzed for both fuels at several operating conditions. The reaction progress of AI kernels as well as their apparent growth rate were evaluated. Results revealed that the stabilization mechanism (i.e. lifted flame or isolated kernel) strongly depends on the turbulent mixing, co-flow temperature and fuel composition. A further statistical analysis of the heat release rate (HRR) zones, calculated as the product of the CH2O- and OH-PLIF signals, delivered an indication on the different AI characteristics of C2H4 and CH4. An evaluation of the temporal evolution of the HRR for C2H4 jets provided a deeper insight about the reaction progress at different conditions of the co-flow, when AI was initiated by isolated kernels. Finally, estimations of the apparent growth rate of AI kernels indicated a faster propagation of C2H4 kernels when compared with those of CH4.

Flowering Syndrome-Hybrid Performance Relationship in Maize 2- Grain Yield and Yield Components

A field experiment was conducted for 4 seasons on the farm of the Dept. of Field Crop Sci., Coll. of Agric., Univ. of Baghdad in spring and fall plantings in 2014 and 2015. That was to determine the relationship of hybrid performance in maize (Zea mays L.) crosses with early and late selects of inbreds. Four inbreds; Zm19, Zm32, Zm51, and Zm61 were grown and the very early and very late silking plants were selected and selfed for propagation in the first two seasons. The third season involved growing the selects and top-crossing with early and late inbreds (Zm60 and Zm21). The sixteen crosses were planted in season 4 in RCBD of 3 replicates in population density of 83’000 plants. ha-1. The cross (Zm19xZm60) resulted from early select of Zm19 gave significantly higher grain yield (10.52 t. ha-1) compared to its late counterpart (8.19 t. ha-1). The same cross gave higher grain yield than late Zm19 crossed to late inbred (Zm21) (6.64 t. ha-1). Early selects on inbreds crossed to testers showed significant differences in kernel growth rate (KGR), kernel filling duration (KFD) and kernel weight. Values of KGR ranged between 3.2 - 3.5 g. plant-1. d-1, KFD between 35 – 38 d, and kernel weight between 228 – 294 mg. kernel-1. It was concluded that selection on maize inbred populations creates new variations in traits lead to higher grain yield hybrids. Other traits such as ear length, kernel. ear-1, and kernel weight could be good candidates for selection on inbreds that could help developing new high grain yield hybrids.

Maize kernel weight responses to sowing date-associated variation in weather conditions

Variation in weather conditions during grain filling has substantial effects on maize kernel weight (KW). The objective of this work was to characterize variation in KW with sowing date-associated weather conditions and examine the relationship between KW, grain filling parameters, and weather factors. Maize was sown on eight sowing dates (SD) at 15–20-day intervals from mid-March to mid-July during 2012 and 2013 in the North China Plain. With sowing date delay, KW increased initially and later declined, and the greatest KW was obtained at SD6 in both years. The increased KW at SD6 was attributed mainly to kernel growth rate (Gmean), and effective grain-filling period (P). Variations in temperature and radiation were the primary factors that influenced KW and grain-filling parameters. When the effective cumulative temperature (AT) and radiation (Ra) during grain filling were 950°C and 1005.4MJm−2, respectively, P and KW were greatest. High temperatures (daily maximum temperature [Tmax]>30.2°C) during grain filling under early sowing conditions, or low temperatures (daily minimum temperature [Tmin]<20.7°C) under late sowing conditions combined with high diurnal temperature range (Tmax-min>7.1°C) decreased kernel growth rate and ultimately final KW. When sowing was performed from May 25 through June 27, higher KW and yield of maize were obtained. We conclude that variations in environmental conditions (temperature and radiation) during grain filling markedly affect growth rate and duration of grain filling and eventually affect kernel weight and yield of maize.

Persistence and Spreading Speeds of Integro-Difference Equations with an Expanding or Contracting Habitat

We study an integro-difference equation model that describes the spatial dynamics of a species in an expanding or contracting habitat. We give conditions under which the species disperses to a region of poor quality where the species eventually becomes extinct. We show that when the species persists in the habitat, the rightward and leftward spreading speeds are determined by c, the speed at which the habitat quality increases or decreases in time, as well as [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], which are formulated in terms of the dispersal kernel and species growth rates in both directions. We demonstrate that in the case that the species grows everywhere in space, the rightward spreading speed is [Formula: see text] if c is relatively small and is [Formula: see text] if c is large, and the leftward spreading speed is one of [Formula: see text], [Formula: see text], or [Formula: see text]. We also show that it is possible for a solution to form a two-layer wave, with the propagation speeds of the two layers analytically determined.

Experimental investigation on effects of exhaust gas recirculation on flame kernel growth rate in a hydrogen fuelled spark ignition engine

This paper describes the experimental investigation on effects of exhaust gas recirculation (EGR) on flame kernel growth rate (FKGR) in a hydrogen fuelled spark ignition (SI) engine and correlation development for FKGR. A single cylinder, four-stroke, forced air cooled, bi-fuelled (i.e., gasoline and hydrogen) SI engine was selected for this study. The engine was fuelled by gasoline in carbureted mode and by hydrogen using timed manifold injection. The study was carried out for evaluation of FKGR in engine cylinder using gasoline fuel (brake power variation (1.0–2.1)kW), hydrogen fuel (equivalence ratio variation from 0.4 to 0.9) and hydrogen with EGR up to 18% by volume in a SI engine at compression ratio of 7.2:1 and constant engine speed of 3000rpm. It was found from experimental results that the engine operation with hydrogen at equivalence ratio of 0.8 and above caused to combustion knock. The FKGR increased from 6.7m/s to 33.5m/s with respect to increase in equivalence ratio from 0.4 to 0.9. But the FKGR decreased from 16.7m/s to 6.6m/s with respect to increase in EGR from 0 to 18% by volume. In addition to this a correlation was developed for FKGR with equivalence ratio and EGR. The correlation was validated with experimental results, and then simulation study was carried out for simultaneous variation of equivalence ratio and EGR. The notable finding emerged from this study that increase in FKGR with equivalence ratio can be controlled by EGR and there is possibility of engine operation without knock and elimination of backfire at high equivalence ratio.

Modelling of early flame kernel growth towards a better understanding of cyclic combustion variability in SI engines

The analysis of particular effects that influence cyclic combustion variability in spark-ignition engines is presented in this paper. The cycle-simulations are performed over 16 knock-free full load operating conditions of a single cylinder engine fuelled with gasoline. For the modelling of early flame kernel growth a newly developed quasi-dimensional ignition model is applied. The ignition model includes a detailed description of the electric circuit, the electric spark length, the spark plug geometry and the flame kernel growth. The main turbulent combustion is calculated using the extended quasi-dimensional fractal combustion model requiring the correct prediction of in-cylinder turbulence level. The cyclic combustion variability is simulated by a variation of the in-cylinder turbulence level, the flow angle at spark plug and the stratification of air equivalence ratio from cycle-to-cycle. The statistical analysis of the indicated mean effective pressure (IMEP) gives a more detailed quantitative picture of the causes of the cyclic combustion variability in SI engines over the different operating conditions. The variation of in-cylinder turbulence is found to be the dominant factor that affects the cyclic variability (up to 66%), while the variation in the early flame kernel growth rate is responsible for up to 18% of the overall cyclic combustion variability in the modelled SI engine at full load conditions.

Experimental investigation and phenomenological model development of flame kernel growth rate in a gasoline fuelled spark ignition engine

As flame kernel growth plays a major role in combustion of premixed-charge in spark ignition engines for higher energy efficiency and less emission, the experimental study was carried out on a single cylinder spark ignition research engine for measurement of flame kernel growth rate (FKGR) using spark plug fibre optics probe (VisioFlame sensor). The FKGR was measured on the engine at different power output with varied spark ignition timings and different engine speeds. The experimental results indicate that the FKGR was the highest with the maximum brake torque (MBT) spark timing and it decreases with increase in the engine speed. The FKGR at engine speed of 1000RPM was the highest of 1.81m/s with MBT timing (20°bTDC) as compared to 1.6m/s (15°bTDC), 1.67m/s (25°bTDC), and 1.61m/s (30°bTDC) with retarded and advanced timing. In addition to this, a phenomenological model was developed for calculation of FKGR. It was observed from the model that FKGR is function of equivalence ratio, engine speed, in-cylinder pressure and charge density. The experimental results and methodology emerged from this study would be useful for optimization of engine parameters using the FKGR and also further development of model for alternative fuels.

Attainable yield achieved for plastic film-mulched maize in response to nitrogen deficit

Nitrogen (N) stress limits the yields of maize (Zea mays L.) that have been plastic film-mulched in northwest China. Using the tested Hybrid-Maize simulation model, which was combined with field experiments using four levels of N fertilisers (0, 100, 250 and 400kgNha−1), we aimed to understand the variability of the attainable yield in response to N stress under plastic film mulching. We show that the application of N250 or N400 results in 100% simulated potential LAI, which is, thus, close to 100% of the simulated potential of both biomass and grain yield. However, N stress treatments significantly decreased the biomass and grain yields, achieving only 40–50% of the simulated potential (N0 treatment) and 70–80% of the simulated potential (N100 treatment). Growth dynamic measurements showed that N stress significantly decreased the LAI, delaying the source capacity growth (canopies) around the silking stage and resulting in lower final kernel numbers. The lower LAI resulted in decreased dry matter accumulation and allocation during the reproductive stage; this decrease led to a decrease in the kernel growth rate and in the grain filling duration, which resulted in a significantly lower kernel weight. This knowledge could be helpful for the optimisation of N management to close the yield gaps of dryland maize in semi-arid monsoon climate regions.

SOURCE-SINK MANIPULATION EFFECTS ON MAIZE KERNEL QUALITY

Evaluation of source or sink limitations on maize (Zea mays L.) yield and yield components is important for the rational design of agricultural practices as well as breeding strategies. There is little information on how the source or sink limitations during the effective grain-filling period affect final kernel quality. The objective of this study was to evaluate the effect of source/sink manipulation in different times after mid-silking stage on kernel weight (KW), kernel number per square meter (KN m−2), kernel protein and oil of different maize hybrids. Field experiments were conducted at the experimental field of College of Agriculture, Shiraz University, Shiraz, Iran, located at Bajgah (52° 35′ N and 39° 4′ E and 1810 m above sea level, asl) during the 2008 and 2009 growing seasons. The treatments included three hybrids and defoliation that were arranged in the main, and subplots, respectively. Leaves removal treatments were imposed when plants were at the mid-silking stage. Silking was taken as the time when 50% of the plants in a row presented visible silks. Defoliations included control, 50% of defoliation at 25 (early defoliation), and 35 (late defoliation) days after silking (defoliation treatments were applied to all plants of each plot). The experiments were conducted in randomized complete block (RCB) design with three replications and the treatments in a split-plot arrangement. Early defoliation greatly reduced kernel growth rate and grain filling period, resulting in lower mean kernel weight. Defoliation treatments modified KN m−2 and kernel number per ear (KNPE) and variations in these components affected protein and oil content. Decreased source size by defoliation decreased kernel protein content dramatically with no significant change in oil content. Differences among treatments appeared to be related only to the post-flowering source/sink ratio. Therefore, to improve protein yield in maize, hybrids and agronomic practices should aim to increase the post-flowering source/sink ratio.

Correlations Between Parental Inbred Lines and Derived Hybrid Performance for Grain Filling Traits in Maize

ABSTRACTIndividual kernel weight (KW) is largely genetically determined, and its variability is achieved through different combinations of rate and duration of kernel growth. Genetic variability for grain‐filling patterns has been observed among inbred lines and commercial hybrids, and there is current interest on dissecting its genetic basis. However, suitable grain filling phenotyping protocols are still to be determined, such as the value to study traits at the inbred or hybrid levels. The objective of our study was to evaluate the correlation between parental inbred line and derived hybrid performance for several grain‐filling traits in maize (Zea mays L.). We hypothesized that there would be high correlations due to the relative high heritability of grain‐filling traits. Three trials were conducted (two in Argentina and one in the United States) with commercial relevant germplasm (totaling 25 parental inbreds and 31 single‐cross hybrids). Traits were KW, kernel growth rate (KGR), grain‐filling duration (GFD), maximum water content (MWC), moisture concentration at physiological maturity (MCPM), and kernel desiccation rate (KDR) during the effective grain filling. Both heterosis and correlations between midparental value and hybrid performance were significant (p &lt; 0.05) for all traits (r values of 0.63, 0.71, 0.81, 0.83, 0.61, and 0.71 for KW, KGR, GFD, MWC, KDR, and MCPM, respectively). Our results confirm that studying inbred lines for grain‐filling traits generates valuable information for derived hybrid performance.

The effect of planting date on maize: Phenology, thermal time durations and growth rates in a cool temperate climate

Field experiments were established in the Waikato and Manawatu regions of New Zealand over two cropping seasons (2006–2007), differing primarily in rainfall and soil type, to establish how planting date (PD) influenced maize phenology and growth processes across a range of environmental conditions. Though not significantly different to 8°C, a base temperature of 8.6–9.4°C (Tb8.6–Tb9.4) adequately estimated thermal time (TT) durations for the emergence-flowering phase while Tb0 was more satisfactory for estimating grain filling duration.Delayed planting either reduced (Waikato) or increased (Manawatu) the emergence-flowering duration and this was associated with changes in leaf number and phyllochron length. The phyllochron averaged 47°Cd, but increased to 51°Cd when soil temperature, radiation and precipitation between emergence and tassel initiation were respectively >22°C, ≤17MJm−2d−1 and ≤30mm. Sub-optimal temperatures and radiation under late plantings triggered a source limitation, leading to assimilate remobilization, reduced grain filling duration and resulted in higher grain moistures at physiological maturity (36% vs. 30%). When rainfall between emergence and flowering was ≥234mm, increases in average daily irradiance (19.5–21.4MJm−2d−1) and mean temperature (15–18°C) increased pre-flowering crop growth rate (CGR) by 1gm−2(°Cd)−1. With late planting, higher pre-flowering radiation (≥21MJm−2d−1) and temperatures (≥17°C) increased CGR while low post-flowering radiation (13MJm−2d−1) and temperature (15.7°C) reduced CGR. Kernel growth rate (KGR) was more stable across PDs and hybrids when TT was used (0.36–0.38mg (°Cd)−1). Provided temperature was ≥19°C, low daily irradiance (11MJm−2d−1) did not significantly reduce KGR. More rapid leaf senescence occurred for early and late plantings, and this was attributed to source–sink imbalances caused by assimilate accumulation or shortage. Leaf senescence rates in the absence of water stress were 0.03% (°Cd)−1 between anthesis and mid grain-fill, and increased to 0.2% (°Cd)−1 towards the end of grain filling.

Dissecting the genetic basis of physiological processes determining maize kernel weight using the IBM (B73×Mo17) Syn4 population

Knowledge on the genetic bases of physiological processes determining maize kernel weight (KW) is relevant for maize yield improvement. However, little is known about the genetic control of KW and its component traits: kernel growth rate (KGR) and grain-filling duration (GFD). We phenotyped several grain-filling traits in 245 RILs from the IBM Syn4 population (B73×Mo17) under two environments, and a multi-trait multi-environment quantitative trait loci (QTL) analysis was conducted. We were specifically interested in seeking genetic links of known correlated traits at the phenotypic level, like kernel maximum water content (MWC) and KGR. Our specific objectives were (i) to conduct a QTL analysis over grain-filling traits to determine their genetic complexity, (ii) to study the relationships between kernel developmental traits at phenotypic and genetic levels, and (iii) to suggest possible candidate genes for each specific trait using detected QTL and B73 sequence data.All traits showed significant genotype×environment interactions (p<0.001) and large phenotypic variability. KW variability was positively associated (p<0.01) with variations in KGR (r=0.79) and GFD (r=0.32). As expected, KGR was positively correlated to MWC, while GFD was negatively correlated to the kernel moisture concentration at physiological maturity (MCPM). A total of 10 joint QTL were detected under both environments, located on chromosomes 1, 2, 4, 5, 6, 7, 9 and 10. Most QTL showed inconsistent effects underlying genotype×environment interactions. However, the multi-trait multi-environment approach helped understand genetic correlations between traits, where positive and consistent genetic correlations were observed between KW, KGR and MWC on chromosomes 2, 6, 9 and 10. Only one consistent QTL for KW, GFD and kernel desiccation rate (KDR) was detected. KGR and GFD showed no common consistent QTL, supporting previous observations on independent physiological control. Several detected QTL co-localized with previous mapping studies. With the use of B73 sequence data we described genes within QTL marker intervals, and discussed relevant candidate ones for future dissection. Results showing the co-localization of consistent QTL for KW, KGR and MWC suggest a common genetic basis for these critical secondary traits measured under field conditions.

Enhancement of flame development by microwave-assisted spark ignition in constant volume combustion chamber

The enhancement of laminar flame development using microwave-assisted spark ignition has been investigated for methane–air mixtures at a range of initial pressures and equivalence ratios in a 1.45l constant volume combustion chamber. Microwave enhancement was evaluated on the basis of several parameters including flame development time (FDT) (time for 0–10% of total net heat release), flame rise time (FRT) (time for 10–90% of total net heat release), total net heat release, flame kernel growth rate, flame kernel size, and ignitability limit extension. Compared to a capacitive discharge spark, microwave-assisted spark ignition extended the lean and rich ignition limits at all pressures investigated (1.08–7.22bar). The addition of microwaves to a capacitive discharge spark reduced FDT and increased the flame kernel size for all equivalence ratios tested and resulted in increases in the spatial flame speed for sufficiently lean flames. Flame enhancement is believed to be caused by (1) a non-thermal chemical kinetic enhancement from energy deposition to free electrons in the flame front and (2) induced flame wrinkling from excitation of flame (plasma) instability. The enhancement of flame development by microwaves diminishes as the initial pressure of the mixture increases, with negligible flame enhancement observed above 3bar.

Kernel number and kernel weight determination in dent and popcorn maize

Yield formation in maize ( Zea mays L.) dent hybrids has been directly linked to the rate of plant biomass accumulation and partitioning of assimilates to the developing grain. Maize popcorn genotypes have been studied less extensively, but their kernels are known to differ in terms of endosperm structure and typical growth patterns. Our objective was to evaluate how variation in plant growth rate (PGR) at different stages of kernel formation and development affected kernel number per plant (KNP), individual kernel weight (KW) and rate and duration of kernel growth in popcorn genotypes, relative to dent ones. We conducted three experiments (two in Ames, Iowa, and one in Pergamino, Argentina) in which PGRs around flowering and during the linear phase of the grain-filling period of four dent and eight popcorn genotypes were altered by plant density, defoliations and thinning treatments. Yield per plant, KNP, KW, rate and duration of kernel growth all showed significant kernel type (popcorns vs. dents) effects ( p < 0.01). KNP was highly correlated with ear biomass accumulated around flowering in dents and popcorns, and popcorns showed a higher efficiency for setting kernels per unit of ear biomass accumulated around flowering ( p < 0.01). Popcorn inbred R18 in particular showed a significantly higher efficiency, consistent across experiments. Relationships between potential KW at early grain filling or kernel growth rate and the PGR per kernel around flowering were different for dent and popcorn genotypes. Most popcorns established a lower potential KW compared to dent genotypes at similar PGRs per kernel around flowering. Also, popcorn kernels were less prone to decrease KW in response to severe reductions in plant growth during the linear phase of the grain-filling period as promoted by defoliation treatments (significant kernel type × source manipulation treatment interaction, p < 0.001). Despite different patterns of KNP and KW determination, yield variation across dent and popcorn genotypes and environments corresponded closely to the potential sink capacity established by the end of the lag phase 14 days after anthesis. This result emphasizes the importance of the flowering period to establish KN and KW across different maize germplasm.

Adequate zinc nutrition alleviates the adverse effects of heat stress in bread wheat

Zinc (Zn) deficiency and heat stress affect the productivity of cereal crops in many semi arid regions of the world. Zinc nutrition affects membrane integrity and activity of superoxide dismutase (SOD) enzymes which are also important to a plant’s ability to cope with high temperatures. Two experiments were conducted to examine the interaction between Zn nutrition and heat stress at two growth stages. Wheat was grown at deficient and adequate levels of Zn at 22/16°C before being exposed to a short period of high temperature (40/20°C). One experiment examined the response to a 3 day heat stress treatment at 10 days after anthesis and the second experiment examined the response to 6 days of heat stress in 30-day old seedlings. Varieties differing in thermotolerance and sensitivity to Zn deficiency were compared. Zinc deficiency and heat stress reduced kernel growth rates, kernel weight and grain yield and the greatest reductions were measured in Zn-deficient, heat stressed plants. The greater reduction in kernel growth rates from heat stress in Zn deficient plants occurred in both thermotolerant and sensitive varieties and was negatively associated with grain Zn concentration. Genetic differences in tolerance to Zn deficiency did not have consistent effects on the response to heat stress. Chlorophyll fluorescence and chlorophyll content were reduced and chloroplast ultrastructure was disrupted by heat stress and the effect was exacerbated by low supplies of Zn. While the responses to heat stress and low Zn were largely additive effects, the experiments demonstrated that low levels of Zn nutrition can exacerbate the adverse effects of short periods of heat stress on kernel growth and chloroplast function.

Trait dissection of maize kernel weight: Towards integrating hierarchical scales using a plant growth approach

Maize (Zea mays L.) yield is a function of the number harvested kernels per unit land area and the individual kernel weight (KW). Kernel weight and its development show a wide variability due to the genotype, the environment, the crop management, and all possible interactions. Commercial maize hybrids differ markedly in the patterns (rate and duration of kernel growth) behind differences in final KW. The same can be observed when public or elite proprietary maize inbred lines are analyzed. To progress in our understanding of KW variability, we reviewed and discussed current knowledge for analyzing kernel growth as an integrated system, modulated by processes linking different levels of organization (the different kernel tissues, the whole kernel, the plant, the canopy). Ideas on how to integrate this knowledge towards the development of a multi-hierarchical scale framework for predicting KW under different growth environments are currently needed, as they have high relevance for dissecting the genetic basis of kernel growth and maize yield definition at the canopy level. At the kernel and tissue level, we highlight the need of focusing and studying traits like assimilate movement into developing kernels, endosperm cell division, endosperm cell death, kernel internal homeostasis and kernel water relations. These specific processes need to be connected affecting the rate or duration of grain filling at the whole kernel level for studying kernel size variability. At the plant and canopy levels, the dynamic response of both kernel number and potential KW to plant growth around flowering appears critical for understanding KW variations, as maize final KW is highly associated with the potential KW determined during the first stages of grain filling. Focusing on the period around flowering in this species is important for yield improvement through both yield components, kernel number and size. At present it seems that maize potential yield can only be improved by modifying the sink capacity established at the end of the lag phase and increasing the source strength during grain filling so as to fulfill this potential.