Early Reproductive Stages Research Articles

Sensitivity of a crop growth simulation model to variation in LAI and canopy nitrogen used for run-time calibration

Run-time calibration, i.e. adjusting simulation results for field observations of model driving variables during run-time, may allow correcting for deviations between complex mechanistic simulation model results and actual field conditions. Leaf area index (LAI) and canopy nitrogen contents (LeafNWt) are the most important driving variables for these models, as they govern light interception and photosynthetic production capacity of the crop. Remote sensing may provide (spatial) data from which such information can be estimated. How, when and at what frequency such additional information is integrated in the simulation process may have various effects on the simulations. The objective of this study was to quantify the effects of different run-time calibration scenarios for final grain yield (FGY) simulations in order to optimize remote sensing image (RS) acquisition. The PlantSys model was calibrated on LAI and LeafNWt for maize in France and used to simulate maize crop growth in the Argentina and the USA, for which non-destructive estimates of LAI and leaf chlorophyll contents were acquired by optical measurement techniques. Leaf chlorophyll data were used to estimate LeafNWt. Due to its structure, the PlantSys model was more susceptible to run-time calibration with LeafNWt than with LAI. Run-time calibration with LAI showed the largest effect on FGY before and around flowering, and could mainly be related to maintenance respiration costs. Run-time calibration with LeafNWt showed the largest effect on FGY at and after flowering and could mainly be related to the change in effective radiation interception due to change in leaf life. The accuracy of LAI estimates showed a major effect on FGY for underestimations but was small in absolute sense. The accuracy of LeafNWt estimates had significant impact at all crop development stages, but was the strongest after flowering where crop growth and nitrogen uptake are less able to recuperate from changes in LeafNWt. In absolute sense, the effect on FGY was as strong as the accuracy of the LeafNWt estimates when applied in the early reproductive stages. Based on these results it was concluded that remotely sensed in-field variability of LAI and LeafNWt is valuable information that can be used to spatially differentiate model simulations. Run-time calibration at sub-field level may lead to more accurate simulation results for whole fields.

Anticipated yield loss in field-grown soybean under elevated ozone can be avoided at the expense of leaf growth during early reproductive growth stages in favourable environmental conditions

Ozone is a powerful oxidizing agent which is responsible for more damage to vegetation than any other air pollutant. In this study, leaf growth, photosynthesis, and carbohydrate content were analysed during the seed-filling growth stage of field-grown soybeans exposed to ambient air and 1.2 times ambient ozone concentration using a Free Air Concentration Enrichment (FACE) facility. By contrast to predictions based on controlled-environment and open-top chamber studies, final yield did not differ between treatments, although the cultivar used here was sensitive to ozone damage: growth and carbohydrate content of upper canopy leaves was reduced during the seed-filling stage in which an ozone-induced decrease of photosynthesis was present. However, 2004 was an ideal growing season in central Illinois and the cumulative ozone indices were lower than in previous years. Still, the results indicate that the anticipated yield loss under ozone concentrations was avoided at the expense of leaf growth, as reserves were diverted from vegetative to reproductive organs.

A Screening Test for the Determination of Ethylene Sensitivity

Ethephon, which releases ethylene within plant tissues after application, was chosen to perform assessments of the relative sensitivity of crops to ethylene and to determine which stages of plant development were most sensitive. The species chosen were: barley, wheat, oats, canola and field pea, all of which are important crops in the province of Alberta, Canada. Plants were treated with ethephon at one of 7 different stages. Plants were assessed for their vegetative and reproductive growth, including height, biomass, yield and seed quality. Visual symptoms were photographed and documented to compare them with symptoms caused by ethylene applied as a gas. It was concluded that in barley, wheat and canola the late vegetative and early reproductive stages were most sensitive, at least when sensitivity was defined as reductions in yield and quality. As for field pea, ethephon had no effect on yield but did cause increased numbers of pods, which in certain conditions could lead to increased yields. Significant effects on vegetative growth were only observed in the early vegetative stages of development but with no effects on yield. The screening protocol successfully identified sensitive cultivars and growth stages for further investigation of the effects of ethylene exposure.

Response of soybean sudden death syndrome to tillage and cultivar

Sudden death syndrome (SDS), caused by Fusarium solani f. sp. glycines, is a season-long root disease of soybean (Glycine max) with foliar symptoms beginning in late vegetative and early reproductive stages of plant growth. The disease has been reported in most soybean-growing regions of the United States of America and the world. Previous research found that SDS was less severe in areas that were subsoiled when compared with those with no-till. The objectives of the current study were to determine (i) if cost-effective tillage practices, i.e., chisel plowing and disk tillage, can be efficient in reducing SDS and (ii) if cultivars with a range of SDS resistance or susceptibility respond differently in SDS expression across various tillage practices. In the fall of 2000 and 2001, plots were established in a field with a history of severe SDS and with a soil type consisting of an Armiesburg silty clay loam. The experiment was organized in a split-plot design with four replications. Main plots were tillage (chisel tillage, disk tillage, and no tillage), and subplots were cultivars randomized in main plots. Twelve cultivars were selected based on resistance or susceptibility to SDS. In 2000, chisel tillage reduced the area under the foliar disease progress curve (AUFDPC) when compared with no-till or disk tillage. In 2001, both chisel and disk tillage reduced AUFDPC similarly when compared with no-till. In 2000, the rate of root infection by the fungus, that is, the area under the root colonization progress curve (AURCPC), was higher in both disk- and chisel-tillage treatments than in no-tillage treatments. In 2001, higher rates of root infection occurred with chisel tillage compared with disk tillage and no-till. Among the cultivars, foliar disease ratings, AUFDPC, and soybean yield differed, but there were no differences in the AURCPC.

Dynamic of the genetic structure of bacterial and fungal communities at different developmental stages of Medicago truncatula Gaertn. cv. Jemalong line J5

The genetic structure of bacterial and fungal communities was characterized in the rhizosphere of Medicago truncatula Gaertn. cv. Jemalong line J5 at five developmental stages (three vegetative and two reproductive stages), and in three compartments (bulk soil, rhizosphere soil and root tissues). The genetic structure of microbial communities was determined by cultivation-independent methods using directly extracted DNA that was characterized by automated ribosomal intergenic spacer analysis (ARISA). Principal component analyses (PCA) indicate that, for all developmental stages, the genetic structure of microbial communities differed significantly by compartment, with a major shift in the community in root tissues corresponding to the most intimate compartment with the plant. Differences were also recorded during plant development, the most significant being observed during the transition between vegetative and reproductive stages. Throughout this period, plants were shown to establish the highest level of symbiotic association (mycorrhization, nodulation) with arbuscular mycorrhizal fungi and Rhizobia. During the reproductive stages, the dynamics of the genetic structure differed between bacterial and fungal communities. At the last reproductive stage, the genetic structure of bacterial communities became close to that recorded during the first vegetative stages, suggesting a resilience phenomenon, whereas the genetic structure of fungal communities remained different from the vegetative stages and also from the early reproductive stages, suggesting a persistence of the rhizosphere effect.

Flooding Influences on Growth and Development of Bush Bean Under Greenhouse Conditions

Abstract Crop production in humid climates is often limited by severe thunderstorms that may leave soil flooded or waterlogged for several days. In 2001, a greenhouse study was initiated to determine the tolerance of bush beans (Phaseolus vulgaris L.) to flooding of various durations and at different growth stages. Plants were subjected to eleven flooding treatments lasting from one to eleven days. Flood treatments were initiated when plants reached either early vegetative growth stage (second true leaf open), early reproductive stage (first flower open on the main stem) or late reproductive stage (green seeds fills 1/2 of the pod cavity). In Study 1 flooding during the early vegetative growth stage for one, two and five days resulted in both the number of pods produced and pod fresh weight being statistically similar to that of the non-flooded control. The remaining flood treatments resulted in pod fresh weights 73% or less than the control weight. The number of surviving plants had more influence on the...

Nitrogen Application to Soybean at Early Reproductive Development

Nitrogen application during soybean [Glycine max (L.) Merrill] reproductive stages has the potential to increase soybean productivity. The objective of this study was to determine the impact of N fertilizer applied to the soil at the beginning pod growth stage on soybean yield and grain quality. Additional objectives were to study alternative N fertilizer and application practices that might enhance soybean use of applied N. A field study was conducted at five locations in Iowa during 1999 and 2000. Nitrogen treatments were urea and polymer‐coated urea broadcast and subsurface band placed between the rows at 45 and 90 kg N ha−1 and a no‐N control. The study showed few, small, and inconsistent effects of N material, placement, and rate on grain yield and quality components at individual sites or when combined across individual sites. There were no significant effects on grain yield, with only a 39 kg ha−1 increase from applied N. Grain protein, oil, and fiber concentrations were the same with or without N application. Aboveground plant dry matter (DM) at the R6 growth stage was greater with the higher N rate, but plant DM with N application was lower than the no‐N control. Nitrogen concentration in plant DM was significantly increased with applied N. In conclusion, N application increased N concentration in R6 soybean plants, but N rate and alternative application practices had no positive effect on plant DM, grain N concentration and removal, grain yield, or grain quality components. It was concluded that growers should not consider fertilizer N applied to soil during early reproductive stages as a method to increase soybean yield or grain quality.

Evaluating Corn Nitrogen Variability via Remote-Sensed Data

Transformations and losses of nitrogen (N) throughout the growing season can be costly. Methods in place to improve N management and to facilitate split N applications during the growing season can be time consuming and logistically difficult. Remote sensing (RS) may be a method to rapidly assess temporal changes in crop N status and to promote more efficient N management. This study was designed to evaluate the ability of three different RS platforms to predict N variability in corn (Zea mays L.) leaves during vegetative and early reproductive growth stages. Plots (15 × 15 m) were established in the Coastal Plain (CP) and in the Appalachian Plateau (AP) physiographic regions each spring from 2000 to 2002 in a completely randomized design. Treatments consisted of four N rates (0, 56, 112, and 168 kg N ha−1) applied as ammonium nitrate (NH4NO3) replicated four times. Spectral measurements were acquired via spectroradiometer (λ = 350–1050 nm), Airborne Terrestrial Applications Sensor (ATLAS) (λ = 400–12,500 nm), and the IKONOS satellite (λ = 450–900 nm). Spectroradiometer data were collected on a biweekly basis from V4 through R1. Due to the nature of satellite and aircraft acquisitions, these data were acquired per availability. Chlorophyll meter (SPAD) and tissue N were collected as ancillary data, along with each RS acquisition. Results showed vegetation indices derived from hand-held spectroradiometer measurements as early as V6–V8 were linearly related to yield and tissue N concentration. The ATLAS data were correlated with tissue N at the AP site during the V6 stage (r 2 = 0.66), but no significant relationships were observed at the CP site. No significant relationships were observed between plant N and IKONOS imagery. By using a combination of the greenness vegetation index and the normalized difference vegetation index, RS data acquired via ATLAS and the spectroradiometer could be used to evaluate tissue N variability and to estimate corn yield variability given ideal growing conditions.

Pod set related to photosynthetic rate and endogenous ABA in soybeans subjected to different water regimes and exogenous ABA and BA at early reproductive stages.

The physiological reasons for reduced pod set in soybean (Glycine max) caused by drought during anthesis are not established. The objective of this study was to investigate the involvement of photosynthetic rate (A), pod endogenous abscisic acid (ABA) and exogenously applied ABA and 6-benzylaminopurine (BA) in regulating pod set in soybean during drought. Two pot experiments were done in a controlled-environment glasshouse. In expt I, soybeans were either well-watered (WW) or droughted by withholding water from 4 d before to 4 d after anthesis (DAA). In expt II, soybeans were drought-stressed (DS) from -4 to 4 DAA. From -2 to 4 DAA, some of the WW and DS plants were treated with 0.1 mm ABA or 1 mm BA. Drought stress decreased A, but increased pod ABA concentration ([ABA]). Pod set decreased only when A had decreased by 40 %, and pod [ABA] had increased 1.5-fold. Beyond the thresholds, pod set correlated positively with A and negatively with pod [ABA]. Exogenously applied ABA decreased A and pod set in WW plants, whilst it increased A and pod set in DS plants; exogenous BA had opposite effects. In these plants, pod set correlated linearly with A. Drought-induced decrease in A is significant in inducing pod abortion, probably as a consequence of carbohydrate deprivation. The effects of ABA and BA on pod set may be partially due to their effects on photosynthate supply.

Effect of rainfall and temperature distribution on incidence of American bollworm on cotton in Haryana

The effect of rainfall and temperature distribution on the incidence of American bollworm on cotton in Haryana state has been studied. Higher rainfall coupled with moderate temperature from early vegetative stage till the early reproductive stage has been found to favour the incidence of the pest during the later stages of the crop. The weather conditions were nearly the same during the later stages (when the infestation is maximum) indicating that the distribution of rainfall and temperature during the early stages determines the infestation.

Transcriptional programs of early reproductive stages in Arabidopsis.

The life cycle of flowering plants alternates between a diploid sporophytic and a haploid gametophytic generation. After fertilization of each the egg and central cells by one male gamete, the development of both fertilization products occurs coordinated with the maternally derived seed coat and carpel tissues forming the fruit. The reproduction program is likely to involve the concerted activity of many genes. To identify genes with specific functions during reproduction, we have analyzed the expression profile of more than 22,000 genes present on the Arabidopsis ATH1 microarray during three stages of flower and fruit development. We found 1,886 genes regulated during reproductive development and 1,043 genes that were specifically expressed during reproduction. When compared to cells from an Arabidopsis suspension culture, S-phase genes were underrepresented and G2 and M-phase genes were strongly enriched in the set of specific genes, indicating that important functions during reproduction are exerted in the G2 and M phases of the cell cycle. Many potential signaling components, such as receptor-like protein kinases, phosphatases, and transcription factors, were present in both groups of genes. Members of the YABBY, MADS box, and Myb transcription factor families were significantly overrepresented in the group of specific genes, revealing an important role of these families during reproduction. Furthermore, we found a significant enrichment of predicted secreted proteins smaller than 15 kD that could function directly as signaling molecules or as precursors for peptide hormones. Our study provides a basis for targeted reverse-genetic approaches aimed to identify key genes of reproductive development in plants.

Using Remote Sensing to Assess Stand Loss and Defoliation in Maize

Assessing hail and wind damage to crops is a difficult, laborintensive task. A quick and accurate method of determining losses could lead to better crop management decisions, more accurate insurance claim adjustment, and reduced expenses for the crop hail insurance industry. Radiometric data were collected in 1997, 1998, and 1999 in Indiana and Nebraska from field plots of maize, Zea mays L., subjected to varying levels of damage. Incremental differences in plant damage resulted in incremental differences in spectral responses. The red and near-infrared spectral bands provided the most discrimination among levels of damage. Classification of remotely sensed images by damage level was performed by extrapolating spectral information from areas where damage levels were known to adjacent unknown areas of damage. Depending on location, sensor, and date of data collection, it was possible to classify the degree of early-season stand loss at accuracies of 48 to 100 percent. For leaf loss during the late vegetative stages, it was possible to classify the degree of leaf loss at accuracies of 81 to 100 percent and, for leaf loss during the early reproductive stages, it was possible to classify damage at accuracies of 71 to 98 percent. These results indicate that remote sensing could be used to improve the accuracy of estimating crop damage as long as adequate ground reference for different levels of crop damage exists.

Application of thiophanate-methyl at different host growth stages for management of sclerotinia stem rot in soybean

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is an important disease of soybean ( Glycine max L.) in the North Central United States. The incidence of SSR can be reduced by planting partially resistant cultivars and by implementation of cultural practices that limit pathogen activity. Fungicides such as thiophanate-methyl are another option for control of SSR, but usually recommended in situations where susceptible cultivars must be grown or modification of cultural practices are not disease control options. Previous studies have shown that control of SSR with fungicides is possible, but that the degree of control is inconsistent especially when incidence of SSR surpasses 50%. This study was designed to evaluate the efficacy of single or multiple applications of thiophanate-methyl in relation to timing of inoculation and early reproductive growth stages of the host. Inoculum was introduced at growth stage R2 at the Illinois location, and naturally occurring inoculum was relied upon to initiate SSR at the Wisconsin location. Thiophanate-methyl was effective when applied at R1 prior to inoculation at R2, but not if applied at R3, after inoculation. Two applications of thiophanate-methyl starting at R1 or the R2 growth stage and a second 2 weeks later lowered the incidence of SSR at the naturally infested Wisconsin site compared to one application with one exception. The incidence of SSR was identical for one and two applications starting at R1.5. Soybean yield was improved by fungicides at both experimental locations, and coincided with timing, and number of applications. Data from both locations suggested that fungicides need to be applied prior to inoculum arrival to the infection court. One application was effective in the controlled inoculation study, but two applications were needed at the naturally infested location. Two applications of thiophanate-methyl improved yield of a partially resistant soybean cultivar even though the incidence of SSR was <10% at the Wisconsin location. Thiophanate-methyl is an effective option for control of SSR, especially to reduce seedborne inoculum in commercial seed production systems.

Seasonal N uptake and N2fixation by common and adzuki bean at various spacings

The adzuki bean (Vigna angularis (Wild.) Ohwi and Ohashi) and common bean (Phaseolus vulgaris L.) have a high physiological demand for N. A 2-year field study was conducted to investigate the seasonal change of available soil N and symbiotic N2 fixation usage. The beans were seeded at two densities, 22.2 plants m−2 with a row spacing of 0.3 m and 11.1 plants m−2 with a row spacing of 0.6 m. The amount of fixed N2 in the shoot was calculated using the 15N natural abundance method. The common bean demonstrated low N2 fixation and the ability to accumulate high levels of soil N. Soil nitrate under the common bean was continually absorbed. The adzuki bean, on the other hand, had a remarkable peak of N accumulation in the early reproductive stage. This was mainly due to N2 fixation, though the soil nitrate level was high. Narrowing the plant row spacing increased the dry matter yield of both species, but the origin of the increased N differed between the species. For the first 77 DAP in 1999 (73 DAP in 2000) the N increase for both beans was due to both soil and atmospheric N2. At harvest, though, the increase of N in common bean was mainly due to soil N, while that in adzuki bean was mainly due to atmospheric N2. It can be concluded that the low symbiotic N2 fixation ability of common bean was due to its high soil N uptake ability and constant N accumulation, which enabled an efficient soil N absorption. Adzuki bean absorbed N mainly for a short period and depended more on symbiotically fixed N2 and, in contrast to common bean, left a high level of NO3-N remaining in the soil after cropping.

Effect of Foliar Application of Urea on Reproductive Abscission and Grain Yield of Soybean

Soybean (Glycine max L., Merr.) is considered to have relatively high level of reproductive abscission, but research information on how fertilizer use influences this problem is scanty. Field trials were therefore carried out for two seasons (1996 and 1998) to investigate the abscission levels of three soybean cultivars (TGX 536‐02D, TGM 579, and Samsoy 11) as affected by foliar application of urea during the early reproductive stages. Flowering was not significantly increased by urea application, although all fertilized plants had fewer flower abortions than control. Fertilizing twice at full‐flowering and pod‐setting (R2–R3) or thrice at first‐flowering, full‐flowering, and pod setting (R1–R2–R3) stages gave the least flower abortion. In TGX 536‐02D the average flower abortion was 61% in 1996 and 57% in 1998. The abortion rate was about 60% for TGM 579 in 1996 and Samsoy 11 in 1998, respectively. Percentage pod abortion was generally reduced especially at the R1–R2–R3 stage, while the proportion of aborted grains was highest in the unfertilized plants. Fertilizing at R2–R3 and R1–R2–R3 reduced seed abortion by about 8% in TGX 536‐02D. The grain yield of fertilized soybean was between 6 and 68% higher than the control. These increases were attributed to higher number of pods and meaningful reductions in flower and pod abortions. Foliar applied urea at R2–R3 gave satisfactory results but the best stage of application was R1–R2–R3.

Dwarf sunflower response to row spacing, stand reduction, and defoliation at different growth stages

Growth compensation of dwarf sunflower (Helianthus annuus L.) hybrids to low initial stands, later stand losses, or plant defoliation has not been reported regarding replanting decisions and crop insurance yield loss assessment. Three experiments were conducted to study the affect of stand reduction, defoliation, and row spacing on dwarf sunflower yield and quality when grown in eastern North Dakota. Experiment 1 evaluated stand reduction (0, 25, 50 and 75%) applied at growth stages (V4, R1 and R6) in 15, 45 and 76 cm spaced rows. Row spacing interactions with stand reduction and growth stage were not significant for yield indicating growth stage and stand reduction effects on yield response were independent of row spacing. In exp. 2, significant growth stage (V4, V8, R1, R2, R3, R5 and R6) by stand reduction (0, 12, 25, 37, 50, 62 and 75%) interaction showed stand reduction at vegetative growth stages not influencing yield, but as maturity progressed yield reductions became greater with increased stand reduction. Achene weight increased with increasing stand reduction at vegetative and early reproductive stages. A reciprocal relationship was noted between achene weight and achene oil content where oil content decreased as achene weight increased. Interaction of growth stage (R1 and R6) and defoliation (0, 25, 50, 75 and 100%) in exp. 3 indicated greater reduction in yield, test weight, 1000-achene weight, and achene oil conte nt as defoliatin increased at growth stage R6. Yield compensating ability of dwarf sunflower is dependent on type and level of damage and growth stage of occurrence, with total yield reduction considering all effects. Key words: Sunflower, Helianthus annuus L., row spacing, stand reduction, defoliation

Hydraulic and chemical signals in the control of leaf expansion and stomatal conductance in soybean exposed to drought stress.

Both hydraulic and chemical signals are probably important in regulating leaf growth and stomatal conductance of soybean (Glycine max L. Merr.) under drought stress. However, until now they have not been investigated concomitantly in this species. To explore this, a pot experiment in a temperature-regulated greenhouse was conducted, in which plants were subjected to progressive drought during early reproductive stages. Biophysical parameters, viz. relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA], xylem pH and xylem [ABA] were followed in control and stressed plants. Drought stress decreased relative leaf expansion rate, stomatal conductance and leaf turgor, whereas it increased leaf [ABA], xylem pH and xylem [ABA]. As soil dried, significant differences between water treatments for relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA], xylem pH and xylem [ABA] were observed at 14, 9, 14, 14, 14 and 9 d after imposition of stress, respectively. The relationships of relative values for relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA] and xylem pH to the fraction of transpirable soil water (FTSW) were well described by linear-plateau functions that allowed calculation of the soil-water thresholds at which processes in stressed plants began to diverge from well-watered controls. The soil-water threshold for stomatal conductance (0.64) was significantly higher than that for relative leaf expansion rate (0.29), xylem pH (0.28), leaf [ABA] (0.27) and leaf turgor (0.25). Relative xylem [ABA] increased, first linearly (when FTSW > 0.5) and then exponentially (when FTSW < 0.5) with decreasing FTSW. Relative stomatal conductance decreased exponentially with increasing relative xylem [ABA] (r2=0.98). Decreased stomatal conductance coincided with an increase in xylem [ABA] and occurred before any significant change of leaf turgor could be detected, indicating that chemical signals (seemingly root-originated ABA) control stomatal behaviour at moderate soil water deficits. Relative relative leaf expansion rate was linearly correlated with relative leaf turgor (r2=0.93), relative xylem pH (r2=0.97) and relative leaf [ABA] (r2=0.98), implying that both hydraulic and chemical signals were probably involved in regulation of leaf expansion at severe soil water deficits.

Development, growth and yield of late-sown soybean in the southern Pampas

Soybean/wheat double cropping is becoming a key component of farming systems in the southern Pampas. In contrast to milder environments, where reduced seed number and shorter duration of early reproductive stages (between R1, one open flower at any node, and R5, 3 mm-long seed in a pod at one of the four uppermost nodes) account for most of the variation in the yield of late-sown soybean, it is proposed that seed weight and duration of later stages (R5 to R7, physiological maturity) are also important in a cooler environment. To evaluate this hypothesis, the yield and yield components of late-sown soybean, as if double-cropped after wheat, were measured in an environment where radiation and temperature fall sharply in late summer (37°S). We carried out a factorial experiment that combined seasons (dry, 1998 and wet, 1999), sowing dates (mid December and early January), cultivars (maturity group II and III), inter-row spacings (0.19 and 0.38 m) and water regimes (dryland and irrigated). This research established a new environmental boundary for soybean performance in soybean/wheat double cropping, moving into temperatures 2 to 4 °C below those in the cooler environments reported in the literature. Yield ranged from 3.7 t ha −1 in irrigated, early sown crops to 2.2 t ha −1 in late-sown dryland crops. Significant interactions between sowing date and other experimental sources of variation were detected that highlight the complex process involved in yield determination. Averaged over all sources of variation, delayed sowing reduced yield at a rate about 2% d −1 from mid December. Seed number accounted for 86, shoot biomass for 66 and harvest index for 56% of the variation in yield. Early-sown crops had heavier seed than their late sown counterparts, i.e. 136 vs. 118 mg seed −1. The decline in crop biomass, harvest index, seed number and individual seed weight with delayed sowing can be attributed to three main factors: (i) shorter season length, (ii) slow growth rate associated with short days, and low temperature and radiation, and (iii) a dramatic reduction in the relative duration of key phenostages, chiefly the period from R5 to R7 which accounted for 77% of the variation in yield, 56% of the variation in seed number and 62% of the variation in seed weight. Crop management practices for late sown soybean are discussed.

Physiological Condition and Reproductive Consequences in Adelie Penguins

Animals must make "decisions" (e.g., when or whether to breed, the effort to put into a breeding episode) by integrating physiological, environmental and social inputs. This integration can be studied only in a field context. In Adélie penguins (Pygoscelis adeliae) reproduction is constrained by foraging ecology, mode of transport, and the extreme latitude at which they live. The decision whether to breed in a given year is influenced by body conditions. Adélie penguins must fast for several weeks during the early reproductive stages and use stored fat for metabolic energy. Females that return to the colony, but do not breed, are 10-12% lighter than females that do breed. Birds that are relatively low in body mass tend to have lower reproductive success than heavier birds, and an individual's reproductive success is positively correlated with the body fat stores it had on arrival. After eggs are laid, parents alternate in attending the nest. Nest failure occurs if one parent does not make a timely return and its fasting partner must eventually leave. During normal-length fasts plasma corticosterone and glucose levels do not change. Blood β-hydroxybutyrate levels gradually increase during the fast while uric acid levels remain low, but in birds with the longest fasts (>∼50 days), ketone levels may fall and uric acid levels increase, indicative of a switch from using fat to using body proteins for metabolism. In incubating males, hematocrit and hemoglobin concentrations also increase, suggesting dehydration can accompany energy stress during the breeding fast.

Impact of 2,4-DP and BAP upon pod set and seed yield in soybean treated at reproductive stages

A large number of soybean (Glycine max L. Merr.)flowers and young pods abscise rather than develop into mature pods. Flower andpod drop or abortion accounts for the majority of total reproductive abscissionand influences potential soybean yield. The objectives of this study were todetermine the patterns of flower, pod and seed development under treatmentswiththe growth regulators, 2-(2,4-dichlorophenoxy) propanoic acid (2,4-DP) and6-benzylaminopurine (BAP), applied at the early reproductive stages, and toexamine the association of reproductive abscission with growth characteristicsand agronomic traits, including seed yield and seed weight. Small seeded [cvPungsan (11.1 ± 0.4 g100-seed−1)] and large seeded [cv Manlee(21.0 ± 0.5 g 100-seed−1)]genotypes were separately planted in the greenhouse and field, and treated witheither 2,4-DP or BAP. 2,4-DP (a synthetic auxin) and BAP (a syntheticcytokinin)were each applied at three concentrations (i.e. high, intermediate or low):0.12mM, 0.08 mM, 0.04 mM, and 1.5mM, 1 mM, 0.5 mM respectively. High andlow concentrations were employed for greenhouse experiments to examine thenumber of flowers per plant in pots. With the exception of low BAP (0.5mM) treatment in Pungsan, all treatments increased total podnumberwith various numbers of seeds per pod. Low 2,4-DP (0.04 mM) inbothgenotypes or BAP (0.5 mM) in Manlee significantly reduced flowerabortion and delayed abscission of pods in both genotypes, resulting inincreased pod setting rates. Under field conditions using intermediateconcentrations, 1 mM BAP significantly increased 100-seed weightto22.3 g at R1 in Manlee and 11.9 g at R3 in Pungsan.BAP (1 mM) at R3 in Pungsan significantly improved seed yield(40.1g plant−1). Maturity was not significantlyaffected by either application in Manlee, but was significantly affected by BAPin Pungsan. In Pungsan, 2,4-DP increased pod number, plant height and nodenumber, but decreased 100-seed weight in Pungsan treated at R1, causing nosignificant change of seed yield. This study suggested that exogenousregulatorssignificantly influenced reproductive and growth characteristics, andconsequently seed yield, but increase of pod number was not always beneficialfor seed yield.