Stages Of Reproductive Development Research Articles

An object-oriented model of the morphological development and digestibility of perennial ryegrass

An object-oriented simulation model was developed to integrate detailed analyses of perennial ryegrass ( Lolium perenne) plant part dimensions, and their mass, cell wall content (CWC) and cell wall digestibility (CWD). The model was validated against data from two field experiments, carried out in The Netherlands (52°N) and Norway (67°N). In the experiments, the effects of temperature × daylength interactions on development, growth and digestibility were determined. Three cultivars differing in heading date were used, and undisturbed growth and regrowth after early (only in The Netherlands) and late cutting were studied. The sensitivity of the model was tested for changes in parameters determining morphological development. A grass plant was modelled as an aggregation of shoot objects. A shoot is an aggregation of phytomers, plus an inflorescence in the reproductive development stage. A phytomer consists of a leaf blade, a leaf sheath, a stem internode and a root. Each phytomer has an axillary bud, which can develop into a new shoot. Morphological development, organic matter (OM) growth and composition were simulated well by the model. Only for regrowing crops in The Netherlands CWC was lower and CWD was higher in the simulations than observed in the field, whereas the differences increased when stem development was more advanced at the moment of cutting. This was attributed to residual stems in the stubble after cutting due to difficulties with machine cutting of lodged crops on the experimental plots. The model can be considered as sufficiently accurate to simulate OM yield and composition of grass cultivars differing in heading date and growing under strongly contrasting temperature and daylength conditions. When the leaf appearance rate, width or length of the leaf blade were increased in the sensitivity analysis, OM yield enhanced, but composition and digestibility of the reproductive grass crops were not systematically affected.

An object-oriented model of the morphological development and digestibility of perennial ryegrass

An object-oriented simulation model was developed to integrate detailed analyses of perennial ryegrass (Lolium perenne) plant part dimensions, and their mass, cell wall content (CWC) and cell wall digestibility (CWD). The model was validated against data from two field experiments, carried out in The Netherlands (52°N) and Norway (67°N). In the experiments, the effects of temperature × daylength interactions on development, growth and digestibility were determined. Three cultivars differing in heading date were used, and undisturbed growth and regrowth after early (only in The Netherlands) and late cutting were studied. The sensitivity of the model was tested for changes in parameters determining morphological development. A grass plant was modelled as an aggregation of shoot objects. A shoot is an aggregation of phytomers, plus an inflorescence in the reproductive development stage. A phytomer consists of a leaf blade, a leaf sheath, a stem internode and a root. Each phytomer has an axillary bud, which can develop into a new shoot. Morphological development, organic matter (OM) growth and composition were simulated well by the model. Only for regrowing crops in The Netherlands CWC was lower and CWD was higher in the simulations than observed in the field, whereas the differences increased when stem development was more advanced at the moment of cutting. This was attributed to residual stems in the stubble after cutting due to difficulties with machine cutting of lodged crops on the experimental plots. The model can be considered as sufficiently accurate to simulate OM yield and composition of grass cultivars differing in heading date and growing under strongly contrasting temperature and daylength conditions. When the leaf appearance rate, width or length of the leaf blade were increased in the sensitivity analysis, OM yield enhanced, but composition and digestibility of the reproductive grass crops were not systematically affected.

Caracterização bioquímica e cinética de lipoxigenases de folhas de soja submetidas à remoção dos primórdios florais

O uso da soja [Glycine max (L.) Merrill] na alimentação humana tem encontrado dificuldades devido ao seu sabor característico (beany flavor), que é derivado da ação das lipoxigenases (EC 1.13.11.12). Ao contrário das lipoxigenases de sementes de soja, que têm sido extensivamente estudadas, a diversidade e características das lipoxigenases de folhas não estão totalmente elucidadas. Sabe-se que além de sua atividade catalítica, as lipoxigenases de folhas estão envolvidas no armazenamento temporário de nitrogênio e na resposta da planta ao estresse. Com o objetivo de investigar o efeito da remoção dos primórdios florais na atividade das lipoxigenases de folhas de soja, foram utilizados dois genótipos de soja: IAC-100, uma variedade com presença de lipoxigenases na semente e IAC-100 TN, uma linhagem com ausência completa de lipoxigenases na semente. Por meio de dados da cinética enzimática, foram constatados dois picos mais acentuados de atividade em pH 5,0 e 6,5, com temperatura ótima de 25ºC. Para ambos os genótipos, as atividades foram maiores nos tratamentos que nos respectivos controles. Os valores de KM app aos 16 dias, nas plantas-controle, foram semelhantes para os dois genótipos, sugerindo não haver influência da manipulação genética das lipoxigenases na semente em relação à expressão dos genes que codificam as lipoxigenases de folhas. No entanto, os valores de KM app foram diferentes entre a fase vegetativa e a reprodutiva, em ambos genótipos, indicando pools distintos de isoenzimas lipoxigenases entre as duas fases.

Genomic regions governing soybean seed nitrogen accumulation

AbstractNitrogen accumulation in the form of seed protein takes place in soybean [Glycine max (L.) Merr.] during the reproductive stages of development. The purpose of this study was to relate genotypic differences in seed nitrogen accumulation with genomic regions controlling nitrogen accumulation in soybean during R5, R6, and R7 growth stages. A population of 101 F6∶8 recombinant inbred lines (RIL) developed from a cross of N87‐984‐16×TN93‐99 was utilized. The RIL were grown at the University of Tennessee, Knoxville Experiment Station, in a randomized complete block design with three replications in 2002. Seed nitrogen was determined from pod samples harvested at the R5, R6, and R7 growth stages. A significant (P<0.05) difference among genotypes was found for nitrogen accumulation at all three growth stages. Single‐factor ANOVA revealed that quantitative trait loci (QTL) governing nitrogen accumulation in soybean seed were distributed in the linkage groups A2, B2, D1a, D1b, E, G, and M. Phenotypic variation explained by an individual QTL ranged from 5 to 11.6%. These QTL may provide useful marker‐assisted selection opportunities for soybean protein improvement.

Genotypic variability of pigeonpea in distribution of photosynthetic carbon at low phosphorus level

Pigeonpea ( Cajanus cajan L. Millsp.) is an important grain protein crop, which thrives in the P-deficient soils of tropical and subtropical Asia. The varietal differences in soil phosphorus uptake and partitioning of the crop are well documented, but the mechanism of carbon distribution between the source and sink at low P supply is not understood. In the present study, the effect of a low P supply on the distribution of photosynthetic carbon of one high-yielding improved hybrid cultivar, ICPH 8 and two low-yielding non-hybrid cultivars, ICPL 87 and UPAS 120, were compared by feeding the plants 13 CO 2 at the vegetative and reproductive stages of development. A low P supply significantly decreased plant biomass, P uptake, average leaf area and photosynthetic activity of all genotypes; the decrease was smallest in ICPH 8 and largest in UPAS 120. ICPH 8 retained more plant biomass at low P supply due to higher P-absorption capacity rather than high P-utilization efficiency. The tolerance of ICPH 8 to low P is mostly related to its maintenance of a high leaf area and rate of photosynthesis. In contrast, P deficiency severely reduced leaf initiation of the sensitive cultivar UPAS 120, and reduced its photosynthesis. Under limiting P supply, partitioning of 13 C increased in favor of the roots in all cultivars, but the resistant cultivar ICPH 8 partitioned less 13 C to roots, and invested more in shoot growth compared to the non-hybrid cultivars. Similarly, partitioning of 13 C to the raceme was greater in ICPL 87 than in the highly sensitive UPAS 120. It is concluded that P deficiency affects primarily sink activity by restricting cellulose biosynthesis in the meristematic sink cells.

Blood steroid profile and in vitro steroidogenesis by ovarian follicles and testis fragments of adult sea lamprey, Petromyzon marinus

The main purpose of the study was to identify the principal gonadal steroids synthesized by male and female sea lampreys, Petromyzon marinus. To achieve this, we used high performance liquid chromatography to separate the steroids in the serum of sexually mature animals, and to separate the steroids produced by gonadal tissue incubated in the presence of radiolabelled precursor steroids, as a means of identifying the major steroidogenic pathways. We were unable to detect evidence of the ‘classical’ steroids, such as 17β-estradiol (E 2) or testosterone (T) in the serum of either male or female lampreys. Instead, the principal chromatographic peaks contained very polar compounds that had elution times consistent with 15α-hydroxylated estrogens and androgens, and there were sex-specific differences in the chemical nature and the quantity of these compounds. Testis fragments or ovarian follicles co-incubated with tritium-labelled pregnenolone ([ 3H]P 5), 17-hydroxyprogesterone ([ 3H]17OHP 4), or androstenedione ([ 3H]A 4), provided additional confirmation that the gonads synthesize a range of very polar steroids, and the metabolites found were consistent with the presence of a 15α-hydroxylated (15αOH) metabolic pathway common to testis and ovary. For ovarian tissue, the major ‘end product’ metabolites from all three precursors were 15αOH-estrogens, and for testis tissue 15α-hydroxyprogesterone (15αOHP 4) and 15α-hydroxytestosterone (15αOHT) and small amounts of 15αOH estrogen. Small amounts of E 2 were also produced by both ovarian (all substrates) and testicular tissue (some substrates). Although it was assumed that the E 2 was synthesized via the aromatization of T, [ 3H]T was not found as an intermediate metabolite. The study suggests that the principal gonadal steroids in sea lamprey are 15α-OH compounds, and that only small amounts of E 2 or T are synthesized by the gonads at this stage of reproductive development. There was no direct evidence of progesterone (P 4) synthesis from [ 3H]P 5, although the metabolites synthesized by both testis and ovary were indicative of a metabolic pathway that involved P 4 as an intermediate.

Plant Reproductive Development during Spaceflight

Reproductive development in microgravity has now been studied in a variety of plants; Arabidopsis, Brassica, and Triticum have been especially well studied. Earlier indications that gravity might be required for some stage of reproductive development have now been refuted. Nevertheless, the spaceflight environment presents many unique challenges that have often compromised the ability of plants to reproduce. These include limitations in hardware design to compensate for the unique environmental characteristics of microgravity, especially absence of convective air movement. Pollen development has been shown to be sensitive to high concentrations of ethylene prevailing on various orbital platforms. Barring these gross environmental problems, androecium and gynoecium development occur normally in microgravity, in that functional propagules are produced. Nonetheless, qualitative changes in anther and pistil development have been shown, and significant qualitative changes occur in storage reserve deposition during seed development. Apart from the intrinsic biological importance of these results, consequences of diminished seed quality when plants are grown in the absence of gravity will detract from the utility of plant-based life support systems. By understanding gravity's role in determining the microenvironments that prevail during reproductive development, counter-measures to these obstacles can be found, while at the same time providing basic knowledge that will have broader agricultural significance.

Effects of elevated temperature and carbon dioxide on seed‐set and yield of kidney bean (Phaseolus vulgaris L.)

AbstractIt is important to quantify and understand the consequences of elevated temperature and carbon dioxide (CO2) on reproductive processes and yield to develop suitable agronomic or genetic management for future climates. The objectives of this research work were (a) to quantify the effects of elevated temperature and CO2 on photosynthesis, pollen production, pollen viability, seed‐set, seed number, seeds per pod, seed size, seed yield and dry matter production of kidney bean and (b) to determine if deleterious effects of high temperature on reproductive processes and yield could be compensated by enhanced photosynthesis at elevated CO2 levels. Red kidney bean cv. Montcalm was grown in controlled environments at day/night temperatures ranging from 28/18 to 40/30 °C under ambient (350 µmol mol−1) or elevated (700 µmol mol−1) CO2 levels. There were strong negative relations between temperature over a range of 28/18–40/30 °C and seed‐set (slope, − 6.5% °C−1) and seed number per pod (− 0.34 °C−1) under both ambient and elevated CO2 levels. Exposure to temperature > 28/18 °C also reduced photosynthesis (− 0.3 and − 0.9 µmol m−2 s−1 °C−1), seed number (− 2.3 and − 3.3 °C−1) and seed yield (− 1.1 and − 1.5 g plant−1 °C−1), at both the CO2 levels (ambient and elevated, respectively). Reduced seed‐set and seed number at high temperatures was primarily owing to decreased pollen production and pollen viability. Elevated CO2 did not affect seed size but temperature > 31/21 °C linearly reduced seed size by 0.07 g °C−1. Elevated CO2 increased photosynthesis and seed yield by approximately 50 and 24%, respectively. There was no beneficial interaction of CO2 and temperature, and CO2 enrichment did not offset the negative effects of high temperatures on reproductive processes and yield. In conclusion, even with beneficial effects of CO2 enrichment, yield losses owing to high temperature (> 34/24 °C) are likely to occur, particularly if high temperatures coincide with sensitive stages of reproductive development.

Influence of the developmental stage of transgenic rice plants (cv. Senia) expressing the cry1B gene on the level of protection against the striped stem borer (Chilo suppressalis)

We carried out a comparative assessment of the resistance against the striped stem borer (Chilo suppressalis) of transgenic plants of a homozygous line (98-9) of rice (cv. Senia) harboring the cry1B endotoxin gene, at a vegetative stage (3–4 leaf stage) and two reproductive developmental stages (booting and heading-ripening). These three developmental stages match those attained by plants in paddy rice fields at successive infestations of striped stem borers in Northeast Spain. Transgenic and non-transgenic plants were infested with L2-stage larvae at these three stages and dissected after 17–21 days of infestation. In non-transformed plants, the larvae grew normally to L4-stage larvae and pupae, but in transgenic-plants the larvae died early in the infestation process. In addition, plant damage was very severe in control plants, while the transgenic plants appeared to be fully protected at all three of the developmental stages tested. Transgenic plants infested at the early vegetative stage developed more tillers than non-infested control-plants. This stimulatory effect was induced by larvae bites at the beginning of the infestation leading to a full recovery of young transgenic plants by compensatory growth. Therefore, transgenic Senia plants expressing the cry1B gene are protected against striped stem borer pest throughout plant development.

Puberty in Female Mice Is Not Associated with Increases in Either Body Fat or Leptin

It has been hypothesized that puberty is triggered when body fat and hence circulating levels of leptin exceed critical thresholds. Four kinds of experiments tested that hypothesis in female mice. When age was the independent variable, body fat and circulating levels of leptin decreased rather than increased before the onset of puberty. When stage of reproductive development was the independent variable, neither body fat nor circulating levels of leptin correlated with the onset of puberty. In sharp contrast, reproductive development was well correlated with body weight. A significant nocturnal peak in circulating levels of leptin was seen before and at all stages of reproductive development, but the highest levels were seen after rather than before the first estrous cycle was initiated. Neither acceleration nor deceleration of puberty by varying the female’s social environment had any effect on either body fat or leptin. There is no support in any of these experiments for the hypothesis that an increase in body fat and thus an increase in circulating levels of leptin triggers puberty in female mice.

Puberty in female mice is not associated with increases in either body fat or leptin.

It has been hypothesized that puberty is triggered when body fat and hence circulating levels of leptin exceed critical thresholds. Four kinds of experiments tested that hypothesis in female mice. When age was the independent variable, body fat and circulating levels of leptin decreased rather than increased before the onset of puberty. When stage of reproductive development was the independent variable, neither body fat nor circulating levels of leptin correlated with the onset of puberty. In sharp contrast, reproductive development was well correlated with body weight. A significant nocturnal peak in circulating levels of leptin was seen before and at all stages of reproductive development, but the highest levels were seen after rather than before the first estrous cycle was initiated. Neither acceleration nor deceleration of puberty by varying the female's social environment had any effect on either body fat or leptin. There is no support in any of these experiments for the hypothesis that an increase in body fat and thus an increase in circulating levels of leptin triggers puberty in female mice.

Lipid Partitioning in the Hydrothermal Vent Shrimp Rimicaris exoculata

Abstract. This study examines the composition and partitioning of lipids in the alvinocarid shrimp Rimicaris exoculata from Mid‐Atlantic hydrothermal vents. Juveniles and adults at different stages of reproductive development were dissected into abdomen, branchial and ovary/hepatopancreas tissues. Each of these tissues was analysed for total lipid and lipid class composition, and fatty acids and fatty alcohols were identified using GC and GC‐MS. Adult and juvenile shrimp differ in the partitioning of lipids between tissues. Juveniles store lipids in the abdomen as wax ester droplets and may use phosphatidyl choline as an additional reserve. Adult shrimp use triglycerides as an energy store, and triglycerides and polar lipids accumulate in ovary and hepatopancreas tissue during reproductive development. The wax ester storage droplets of juvenile shrimp contain high concentrations of n‐3 fatty acids, which are photosynthetically‐derived and thought to be important for reproductive development in crustaceans. These n‐3 fatty acids are concentrated in the ovary and hepatopancreas of adults compared to other tissues. The n‐3 fatty acid content of these adult tissues is well within that estimated for whole juvenile shrimp, supporting the hypothesis that the n‐3 fatty acids putatively required for adult reproduction are stored from the juvenile stage.

Effect of climate and atmospheric change on soybean water stress: a study of Iowa

The anthropogenic increase in radiatively active gases in the atmosphere has been well documented, and there is evidence that suggests an impact of this increase on the earth's climate. Agriculture is vulnerable to climatic changes, and estimating the likely response to such changes is critical. The current work examines the impact of climate change on water stress during the critical periods of soybean [Glycine max (L.) merr.] reproductive development. This is a time of particular interest because soybeans at these stages are believed to be particularly vulnerable to water stress. Climate scenarios from three General Circulation Models (GCMs) were adapted to produce daily, simulated weather datasets for the nine climate centroids (in the state of Iowa). The GCMs were the Goddard Institute for Space Studies (GISS), Geophysical Fluid Dynamics Laboratory, and United Kingdom Meteorological Office (UKMO) models. Soil association datasets were created for two counties within each of the centroids. Simulations were performed for each county and each GCM at climate samples corresponding to climate change at 350, 450, 550, and 650 ppm atmospheric [CO 2], using the mechanistic soybean physiology model GLYCIM. The model provided data on the probability and magnitude of water stress during the reproductive development stages of soybean crops. The results indicated that water stress was most severe during the R2–R5 stages under the UKMO scenarios, and became progressively more severe as climate change progressed. Although stress occurred under the GISS and GFDL scenarios, it did not increase with changing climate.

Quantification of rainbow trout (Oncorhynchus mykiss) estrogen receptor-alpha messenger RNA and its expression in the ovary during the reproductive cycle.

This study developed a quantitative reverse transcription-polymerase chain reaction (RT-PCR) method to measure estrogen receptor-alpha (ERalpha) mRNA in the rainbow trout (Oncorhynchus mykiss). Using RT-PCR, and primers based on the known ERalpha DNA sequence in this species, cDNA sequences representing most of the protein coding region were obtained from ovary poly A(+) RNA. Using these DNA sequences as probes in Northern blot hybridizations confirmed that a single transcript of 4.2 kilobases in poly A(+) RNA could be detected in liver and ovary RNA. For the quantitative RT-PCR assay an internal standard RNA molecule was produced to control for inherent inter-tube differences in amplification efficiency and permit accurate quantification of ERalpha mRNAs. The quantitative RT-PCR assay proved to be highly specific for ERalpha mRNA with a detection limit of 6.9 fg, which corresponds to 273 fg ERalpha mRNA/microg total RNA. The quantitative RT-PCR assay was used to measure the levels of ERalpha mRNA in ovaries of rainbow trout at different stages of reproductive development. Ovarian ERalpha mRNA expression was found during two distinct periods of reproductive development, in pre-vitellogenic ovaries of fish with ovarian follicle diameters (OFDs) </=100 microm and in mid-vitellogenic ovaries with OFDs >1000 microm. ERalpha mRNA could not be detected in the ovaries of fish with OFDs >100 microm but </=1000 microm. The highest levels of ERalpha mRNA were found in late vitellogenic ovaries of fish with OFDs >2000 microm.

Late-instar European corn borer (Lepidoptera: Crambidae) tunneling and survival in transgenic corn hybrids.

Field studies were conducted in 1996 and 1997 to determine injury by and survival of late-instar European corn borer, Ostrinia nubilalis (Hübner), on genetically altered Bacillus thuringiensis Berliner corn, Zea mays L. Cry1Ab events 176, Bt11, MON810, and MON802; Cry1Ac event DBT418; and Cry9C event CBH351 were evaluated. Plants of each corn hybrid were manually infested with two third-, fourth-, or fifth-instar O. nubilalis. Larvae were held in proximity to the internode of the plant above the ear with a mesh sleeve. Larvae were put on the plants during corn developmental stages V8, V16, R1, R3, R4, R5, and R6. This study shows that not all B. thuringiensis hybrids provide the same protection against O. nubilalis injury. Hybrids with B. thuringiensis events Bt11, MON810, MON802, and CHB351 effectively protected the corn against tunneling by late-instar O. nubilalis. Event 176 was effective in controlling late-instar O. nubilalis during V12 and V16 corn developmental stages; however, significant tunneling occurred by fourth instars during R3 and R5. Event DBT418 was not effective in controlling late-instar O. nubilalis during corn vegetative or reproductive stages of development. Whether the B. thuringiensis hybrids satisfied high- and ultra-high-dose requirements is discussed.

Applications in sustainable production

Farmers in the lower corn belt region of the United States need to know how to fertilize soils in order to optimize the efficiency of potassium (K) use by plants under different tillage systems and with high yield management. A field study was conducted from 1994 to 1996 at the Dixon Springs Agricultural Center (DSAC) on a Bonnie silt loam (fine‐silty, mixed, mesic Typic Fluvaquent) soil and at the SIU Belleville Research Center (BRC) on a Herrick silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) soil. No‐till (NT) and spring chisel tillage (CT) systems were compared in a corn (Zea mays L.)‐soybean (Glycine max L.) rotation. Within each tillage system, K rates of 56, 112 and 168 kg K ha‐1 as potassium chloride were combined with four placement methods that included surface broadcast, 25‐cm surface band over the intended row, surface dribble 15 cm to the side of the intended row, and starter placement of 28 kg K ha‐1 5 cm to the side and 5 cm below the seed at planting (with the remainder of the K surface broadcast). The broadcast K placement most often produced the lowest whole plant K composition of corn or soybean tissue when sampled within a month after emergence. This indicated that the broadcast treatment was less efficient than other placement methods in providing K in the early stages of plant development. However, by the reproductive stage of development, there were no differences in leaf K concentrations among the various placement methods for either crop. Increasing K rates almost always increased leaf K concentrations and usually increased early plant growth and yields. Early plant growth and grain yield were affected to a greater degree in corn than soybean. Soybean yields appeared to maximize at 56 kg K ha‐1, whereas corn often showed higher yields (although not always significant) with K rates of 112 and 168 kg ha‐1. Corn usually requires more K than soybean, which would explain its greater responsiveness to K. For corn, the placement method of K was not as critical as rate, even for no‐till, across the six site‐years of this study. Lower yields occurred in 1996 at both locations with the long term banding of K fertilizers over the intended rows of soybean. This is in contrast to a yield benefit from surface banding at other locations or crops as reported in the literature. Weather problems related to a wet spring followed by dry conditions late in the season may have contributed to the atypical results in 1996. These weather problems probably either lead to larger plants early which ran out of water late in the season, or higher accumulated salt concentrations in the root volume which reduced water uptake late in the season.

Effects of Gas-Producing Platforms on Continental Shelf Megafauna in the Northwest Gulf of Mexico: Reproductive Status and Health

One component of the Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX) was to assess the reproductive effort and health (defined as the prevalence and intensity of parasites or pathologies) of mobile macroepifauna collected near-to and far-from gas-producing platforms. The stage of reproductive development as determined by visual inspection or histological analysis was rarely significantly different between near-field and far-field sites. Tissues were examined histologically to determine the prevalence and intensity of parasitism and disease. If a difference in parasitism or pathology existed, individuals collected far-from the platforms typically had higher prevalences while individuals living near-to the platforms usually had higher intensities. Parasitism and disease had little effect on stage of reproductive development except at MU-A85 where individuals with increased disease and parasitism also had decreased reproductive development. Variations in infection intensity were not due to differences in age structure of populations. Larger, older individuals were not consistently more heavily parasitized. Trend in reproductive stage and population health did not follow trends in environmental contamination; the fewest significant differences were observed at the most contaminated platforms. Patterns of differences in parasitism, disease and reproductive effort between the near and far-field stations were platform specific, indicating that the physical and chemical characteristics unique to each platform probably control reproductive effort and levels of disease and parasitism in populations living there. The influence of structure, a variable common to all platforms, did not exert an overriding influence. Mobile taxa such as shrimp exhibited near-field/far-field differences as frequently as the less mobile species such as starfish. Thus, mobile epifauna maintain discrete populations over long-enough time periods to develop different population histories. Shallow-water sites were more likely to exhibit platform-specific near-field/far-field differences in population structure suggesting that trends in water depth and the intensity of seasonality may explain the apparent uniqueness of each platform's effect on population structure and health.

Pollination and Embryo Development inBrassica rapaL. in Microgravity

Plant reproduction under spaceflight conditions has been problematic in the past. In order to determine what aspect of reproductive development is affected by microgravity, we studied pollination and embryo development in Brassica rapa L. during 16 d in microgravity on the space shuttle (STS-87). Brassica is self-incompatible and requires mechanical transfer of pollen. Short-duration access to microgravity during parabolic flights on the KC-135A aircraft was used initially to confirm that equal numbers of pollen grains could be collected and transferred in the absence of gravity. Brassica was grown in the Plant Growth Facility flight hardware as follows. Three chambers each contained six plants that were 13 d old at launch. As these plants flowered, thin colored tape was used to indicate the date of hand pollination, resulting in silique populations aged 8-15 d postpollination at the end of the 16-d mission. The remaining three chambers contained dry seeds that germinated on orbit to produce 14-d-old plants just beginning to flower at the time of landing. Pollen produced by these plants had comparable viability (93%) with that produced in the 2-d-delayed ground control. Matched-age siliques yielded embryos of equivalent developmental stage in the spaceflight and ground control treatments. Carbohydrate and protein storage reserves in the embryos, assessed by cytochemical localization, were also comparable. In the spaceflight material, growth and development by embryos rescued from siliques 15 d after pollination lagged behind the ground controls by 12 d; however, in the subsequent generation, no differences between the two treatments were found. The results demonstrate that while no stage of reproductive development in Brassica is absolutely dependent upon gravity, lower embryo quality may result following development in microgravity.

Relationship between Soybean Sudden Death Syndrome Disease Measures and Yield Components in F6‐Derived Lines

Soybean [Glycine max (L.) Merr.] sudden death syndrome (SDS), caused by Fusarium solani (Mart.) Sacc. f. sp. glycines Roy can cause substantial yield loss. To determine the relationship between SDS and yield components, 16 F6‐derived lines from the cross ‘Pyramid’ ✕ ‘Douglas’ were tested in two southern Illinois locations (Cora and Ridgway) with natural infestation by the SDS pathogen. Plots were rated for disease incidence (DI), disease severity (DS), and reproductive development stage (R). DI and DS were standardized to R6. Disease index (DX) was calculated as DI×DS/9. Individual plant data collected on three plants per plot were DS, total flowers, total pods at R5.5 (mid‐pod‐fill) and R8, total empty and partially filled pods at R8, total seeds, seeds per pod, seed weight per plant, and 100‐seed weight. Seed quality was rated only at Ridgway. The among genotypes (genetic) covariance and the within genotype (environmental) covariance detected significant reductions in yield per unit of DS and DX (whole plot data). The genetic covariance with individual plant DS detected a significant reduction per unit of DS in total seed weight per plant. The environmental covariance with DS detected significant reductions in all yield components except flowers, empty pods, and seed per pod. There was a significant correlation of G✕E effects of most yield components and DS. Generally, genetic and environmental covariances were similar in magnitude and direction, suggesting that test genotypes were similar in the components affected and the degree of yield loss associated with a given level of disease.

Effect of proximity factors on competition between winter wheat (Triticum aestivum) and Italian ryegrass (Lolium multiflorum)

Density and spatial arrangement (rectangularity) effects on the competitive relationships, yield performance, and dynamics in canopy dominance of winter wheat and Italian ryegrass were evaluated using two addition series experiments. In experiment 1, combinations of six densities of each species formed the treatment matrix of addition series. In experiment 2, each species was tested at four densities and three rectangularities (RE) of winter wheat. In monocultures, crop density (plants per square meter) explained 82 to 85% of the total variation in the per-plant biomass of winter wheat in experiment 1. In mixtures of crop and weed, initial wheat density (N1) and initial ryegrass density (N2) and interaction of N1and N2explained 74 to 80% of the total variation in the per-plant biomass of winter wheat and 68 to 79% of Italian ryegrass in experiment 1. Intraspecific competition was apparent between 15 and 90 days after emergence (DAE) in winter wheat and between 90 and 170 DAE in Italian ryegrass. In mixtures, RE influenced plant size of Italian ryegrass up to 50 DAE only. Maximum winter wheat intraspecific competition occurred at 170 DAE, but maximum interspecific competition occurred during reproductive stages in mixtures. High RE increased seed yield, seed size, and harvest index of winter wheat and reduced biomass of Italian ryegrass. Grain yield of winter wheat was reduced up to 92% by competition from ryegrass. Even nine ryegrass plants in 100 winter wheat plants m−2reduced winter wheat grain yield by 33%. However, the extent of loss in winter wheat grain yield was less in RE 16 (wider spacing) than in RE 1 (square planting) or 4 (close row spacing). Winter wheat was the stronger competitor during vegetative stages, but Italian ryegrass became the stronger competitor during the reproductive stages of development. Winter wheat leaves dominated at the top canopy during the vegetative stage, but ryegrass dominated at the top canopy during the reproductive stages. In the top canopy of mixtures at 200 DAE, the leaf area indices (LAI) of ryegrass was 6.6 times greater than winter wheat at RE 1 compared to only 1.6 times at RE 16. Greater LAI of Italian ryegrass in the top canopy reduced photosynthetically active radiation available to winter wheat by 68% at booting stage.