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Fine fescue grasses displace neighboring plants by depositing large quantities of an aqueous phytotoxic root exudate in the soil rhizosphere. Via activity-guided fractionation, we have isolated and identified the nonprotein amino acid m -tyrosine as the major active component. m -Tyrosine is significantly more phytotoxic than its structural isomers o - and p -tyrosine. We show that m -tyrosine exposure results in growth inhibition for a wide range of plant species and propose that the release of this nonprotein amino acid interferes with root development of competing plants. Acid hydrolysis of total root protein from Arabidopsis thaliana showed incorporation of m -tyrosine, suggesting this as a possible mechanism of phytotoxicity. m -Tyrosine inhibition of A. thaliana root growth is counteracted by exogenous addition of protein amino acids, with phenylalanine having the most significant effect. The discovery of m -tyrosine, as well as a further understanding of its mode(s) of action, could lead to the development of biorational approaches to weed control.

Evaluation of salt tolerance in herbaceous perennials was performed with mature potted plants under greenhouse conditions. Six herbaceous perennial species were evaluated for their tolerance to aqueous solutions of various sodium chloride (NaCl) concentrations over a 21 day period by measuring growth, water transpiration, and leaf nutrient content. Potential exists for utilization of these species in somewhat challenging saline environments along roadsides and in urban landscapes. Species evaluated in a mature growth stage included Achemilla mollis, Nepeta x faassenii, Sedum acre, Thymus praecox, Phlox subulata and Solidago cutleri. On the basis of relative growth rate and water transpiration responses to NaCl (0–400 mM) treatments, groundcovers were grouped into three tolerance categories: highly sensitive to salt treatment (S. acre), those with intermediate sensitivity (A. mollis, N. x faassenii, T. praecox, and P. subulata), and those exhibiting tolerance (S. cutleri). Sodium content in leaf f...

Metabolic profiling allows for simultaneous and rapid annotation of biochemically similar organismal metabolites. An effective platform for profiling of toxic pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs) was developed using ultra high pressure liquid chromatography quadrupole time-of-flight (UHPLC-QTOF) mass spectrometry. Field-collected populations of invasive Australian weeds, Echium plantagineum and E. vulgare were raised under controlled glasshouse conditions and surveyed for the presence of related PAs and PANOs in leaf tissues at various growth stages. Echium plantagineum possessed numerous related and abundant PANOs (&gt, 17) by seven days following seed germination, and these were also observed in rosette and flowering growth stages. In contrast, the less invasive E. vulgare accumulated significantly lower levels of most PANOs under identical glasshouse conditions. Several previously unreported PAs were also found at trace levels. Field-grown populations of both species were also evaluated for PA production and highly toxic echimidine N-oxide was amongst the most abundant PANOs in foliage of both species. PAs in field and glasshouse plants were more abundant in the more widely invasive species, E. plantagineum, and may provide competitive advantage by increasing the plant’s capacity to deter natural enemies in its invaded range through production of novel weapons.

The Catskill Mountains of New York State are an important source of wild-collected American ginseng (Panax quinquefolium) and, increasingly, of woods-cultivated ginseng. The objective of this study was to assess genetic diversity among 9 different wild ginseng populations in and adjacent to the Catskill Mountain region of New York State and to compare these to wild populations from other states including Kentucky, Tennessee, North Carolina, Pennsylvania, and Virginia, and one cultivated population from Wisconsin. Randomly amplified polymorphic DNA (RAPD) markers were used to estimate the genetic distance among samples from the 15 populations. Pooled DNA from 10 plants of each of 8 New York populations was initially screened with 64 random primers; subsequently, the 15 primers that exhibited the greatest number of reproducible polymorphic markers were selected for further experimentation. Gel electrophoresis with the selected 15 primers produced 124 highly reproducible polymorphic bands. The ratio of discordant bands to total bands scored was used to estimate the genetic distance within and among populations. Multidimensional scaling (MDS) of the relation matrix showed distinctly separate clusters between New York and non-New York populations, indicating separation between these two groupings. The MDS analysis was confirmed using pooled chi-square tests for fragment homogeneity. This study shows that RAPD markers can be used as population-specific markers for Panax quinquefolium, and may eventually be utilized as markers for ginsenoside assessment.

Terrestrial weeds continue to evolve in association with the rapid global changes in our land-use systems, due to their regenerative strategies, their adaptability to change, and their inherent diversity. Currently, invasive weeds are estimated to cost the United States’ economy up to $35 billion per year, and this total is rapidly increasing, as greater numbers of invasive species become naturalized. Several invasive exotic species have more recently established across New York State, creating difficulties for agricultural producers, roadside and natural areas managers, and homeowners and resulting in millions of dollars expended annually for their control. Three perennials that have become particularly problematic in New York State in recent years in both agricultural and roadside settings include Japanese knotweed (Polygonum cuspidatum Sieb. & Zucc.), mugwort (Artemisia vulgaris L.), and pale swallow-wort (Vincetoxicum rossicum (Kleop.) Barbar.). This review describes their history, biology, ecology, and potential for management and focuses on key characteristics contributing to their spread in New York State and adjacent regions.

Fifteen herbaceous perennials were evaluated in field experiments in two New York State locations to determine their utility in roadside and landscape areas as weed suppressive groundcovers. Four species, Alchemilla mollis, Nepeta x faassenii, Phlox subulata, and Solidago sphacelata were strongly weed suppressive in both managed (weeds removed) plots and unmanaged (weeds not removed) plots. Weed suppressivity of perennial groundcovers was significantly increased in year two in both locations when perennials were well established. The most suppressive perennials showed several similar characteristics likely associated with their successful establishment. Successful groundcovers possessed dense foliage which strongly reduced light transmittance at the soil surface and emerged relatively early in spring. Lamiastrum galeobdolon and Thymus praecox proved to be more successful over a 2-year period when managed by weed removal in early spring. Although Leymus arenarius, a relatively tall monocot, also inhibited weed growth, this species demonstrated invasive characteristics due to its spread outside plots by fast-growing rhizomes.

Summary 1. Establishment success of non-native invasive species is often attributable either to habitat invasibility or inherent species traits. In this study we explored the interplay between these two factors in the establishment, expansion and plasticity in growth of the clonally reproducing invasive weed mugwort Artemisia vulgaris in two contrasting habitats, as well as the potential management practice of monthly mowing. 2. We investigated resource allocation patterns and spatial distribution of ramets originating from two naturalized populations over a 3-year period. Ramets from these morphologically distinct populations were transplanted into each of two contrasting habitats to determine the invasive potential of these populations and the relative resistance of each habitat to invasion. 3. Total ramet production, average ramet height and spatial distribution patterns differed significantly between the two populations, but the degree of variation in the response was habitat dependent. There were no interpopulation differences in total biomass production. Plastic responses in resource allocation patterns, spatial distribution of ramets and relative growth rates were observed, demonstrating differences in invasive potential between the two mugwort populations. 4. The two habitats differed in invasibility. This could have been the result of differences in community structure, competition for available resources, disturbance and/or invader traits. In addition, monthly defoliation (mowing) reduced mugwort ramet production by as much as 90% and as little as 10%. 5. Synthesis and applications. This study demonstrates that variation exists in habitat invasibility, and that intraspecific variation in growth patterns occurs in mugwort. The interaction between habitat traits and species characteristics was found to be important when determining invasion success. We also demonstrated that monthly mowing following the introduction of mugwort can substantially decrease the rate of spread of this clonal species, which may provide an effective management opportunity both for this species and for other clonal invaders.

Allelopathy is defined as the suppression of any aspect of growth and/or development of one plant by another through the release of chemical compounds. Although allelopathic interference has been demonstrated many times using in vitro experiments, few studies have clearly demonstrated allelopathy in natural settings. This difficulty reflects the complexity in examining and demonstrating allelopathic interactions under field conditions. In this paper we address a number of issues related to the complexity of allelopathic interference in higher plants: These are: (i) is a demonstrated pattern or zone of inhibition important in documenting allelopathy? (ii) is it ecologically relevant to explain the allelopathic potential of a species based on a single bioactive chemical? (iii) what is the significance of the various modes of allelochemical release from the plant into the environment? (iv) do soil characteristics clearly influence allelopathic activity? (v) is it necessary to exclude other plant int...

Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization and root exudation. Allelochemical structures and modes of action are diverse, and may offer potential for development of future herbicides. In the past, allelopathy was described by the Romans as a process resulting in the “sickening” of the soil; in particular, chickpea (Cicer arietinum) was described as problematic when successively cropped with other species. Other early plant scientists, such as De Candolle in the 1800s, first described the ability of plant roots to produce toxic exudates. More recently, research has focused on development of weed management strategies using allelopathic crop residues, mechanism of allelochemical action, and gene regulation of allelochemical production. This paper briefly describes a variety of weed and crop species that establishes some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are more highly weed suppressive in managed settings. A new challenge that exists for plant scientists is to generate additional information on allelochemical mechanisms of release, selectivity and persistence, mode of action, and genetic regulation. Armed with this specific information, we can further protect plant biodiversity and enhance weed management strategies in a variety of ecosystems.

Sorghum (Sorghum bicolor) roots exude a potent bioherbicide sorgoleone. Previous work indicates that sorgoleone is produced in living root hairs. We have developed a mist system that resulted in abundant production of root hairs exuding sorgoleone and a mat system that significantly inhibited root hair development and consequently sorgoleone production. Applying Ag+ (an ethylene action inhibitor) at 1.2 mM to the seedlings grown in the mist system also inhibited root hair formation and elongation. Hypoxic conditions in the mist system did not result in the inhibition of root hair growth as compared to the standard air atmosphere (20.8% O2). Applying ethephon (an ethylene-releasing agent) at 0.031 mM to the roots of seedlings grown in the mat system with water running at 1 ml/min reversed the inhibition of root hair development by water movement. These results indicate that either water movement or ethylene can be utilized to manipulate root hair development and sorgoleone production in sorghum seedlings. It is hypothesized that water movement reduced the local ethylene concentration on the root surface and consequently inhibited root hair development of sorghum seedlings grown in the mat system.

Johnsongrass (Sorghum halepense [L.] Pers.) and SX‐17 (Sorghum bicolor × Sorghum sudanese) were investigated microscopically to identify specifically the location of root exudate production. Light, cryoscanning electron, and transmission electron microscopy were used to determine the area of exudate secretion. Light micrographs indicated that the exudate is solely produced by the root hairs. Scanning electron microscopy supported this conclusion. Transmission electron microscopy studies of root hairs support the hypothesis that root exudates are manufactured in the cytoplasmically dense root hair cell in association with smooth endoplasmic reticulum and possibly Golgi bodies. Ultrastructure studies indicated that small globules of cytoplasmic exudate are deposited between the cell wall and the plasma membrane, where they coalesce into larger globules that pass through the cell wall to form droplets near the tip of root hairs.

Plant roots serve a multitude of functions in the plant including anchorage, provision of nutrients and water, and production of exudates with growth regulatory properties. The root–soil interface, or rhizosphere, is the site of greatest activity within the soil matrix. Within this matrix, roots affect soil structure, aeration and biological activity as they are the major source of organic inputs into the rhizosphere, and are also responsible for depletion of large supplies of inorganic compounds. Roots are very complicated morphologically and physiologically, and their metabolites are often released in large quantities into the soil rhizosphere from living root hairs or fibrous root systems. Root exudates containing root-specific metabolites have critical ecological impacts on soil macro and microbiota as well as on the whole plant itself. Through the exudation of a wide variety of compounds, roots impact the soil microbial community in their immediate vicinity, influence resistance to pests, support beneficial symbioses, alter the chemical and physical properties of the soil, and inhibit the growth of competing plant species. In this review, we outline recent research on root exudation and the role of allelochemicals in the rhizosphere by studying the case of three plants that have been shown to produce allelopathic root exudates: black walnut, wheat and sorghum

Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation. Allelochemical structures and modes of action are diverse and may offer potential for the development of future herbicides. We have focused our review on a variety of weed and crop species that establish some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are ...

Laboratory screening studies were conducted to evaluate the allelopathic potential of fine leaf fescues. Of the seven accessions selected from prior field evaluations for weed-suppressive ability, all inhibited root growth of large crabgrass and curly cress in laboratory assays. Grown in agar as a growth medium and in the presence of living fescue seedlings for 14 or 21 days, test species were sensitive depending on the fescue cultivars. Growth inhibition increased when fescue was grown for increasing periods of time in agar. Seedling fescues produced significant quantities of bioactive root exudates, which were released into the agar medium. Bioactive root exudates were extracted from living fescue roots by using methylene chloride. Shoot tissue was extracted in water and the aqueous extract was partitioned against hexane, ethyl acetate, and methylene chloride. Extracts were tested for inhibitory activity on seedling growth as measured by inhibition of curly cress germination and radicle elongation. Root exudates were more toxic (70% inhibition) than shoot extracts (up 40% inhibition), when formulated at 0.25 mg/ml concentration. Light microscopy and transmission electron microscopy were utilized in an attempt to identify the cellular location of production of secondary products contained in bioactive root exudates. Ultrastructural analysis indicated that the exudate is produced in actively dividing tips of fibrous root cells. The mode of release of these exudates into the environment remains unknown.

Seven sorghum accessions were evaluated quantitatively and qualitatively for the composition of their root exudates. Utilizing a unique capillary mat growing system, root exudates were collected from all sorghum accessions. Exudates were subjected to TLC and HPLC analysis to evaluate their chemical composition. Within each sorghum accession, variation existed in the amount of exudate produced and the chemical constituents of each exudate. Sorgoleone was the predominant constituent identified in each accession's exudate. Other closely related compounds, including 5-ethoxysorgoleone, 2,5-dimethoxysorgoleone, three other minor components (MW = 364, 388, and 402), and one unidentified component comprised the minor constituents of the root exudate. Our past work has shown that several of these compounds have potent phytotoxic activity as photosystem II inhibitors, thereby lending further support to the concept that Sorghum spp. are allelopathic and weed suppressive.

Flooded rice soils produce elevated concentrations of soluble manganous manganese (Mn(2+)) that could be potentially toxic to subsequent crops. To provide insight into how soil pore Mn(2+) changes its concentration in a rice and post rice drying soil, we used an artificial microcosm system to follow Mn(2+) concentrations in two different soil types (red sodosol and grey vertosol) and under two irrigation regimes (flooded and saturated). Soil pore water was collected from four different depths of soil (2.5 cm, 7.5 cm, 15 cm and 25 cm) and Mn(2+) concentrations were analysed during and after the rice phase over a one year cycle. Mn(2+) increased with the advancement of anaerobic conditions at all soil depths, but the concentration was higher in flooded soil compared to saturated soil. Initially, the highest concentration of Mn(2+) was found at a depth of 7.5 cm, while at the later stage of rice growth, more Mn(2+) was found in the deepest sampling depth (25 cm). Plants grown in saturated soils showed a delay in flowering of approximately 3 weeks compared to flooded cultures. Moreover, plants grown in flooded soil produced more tillers and leaf area than those grown in saturated soil. Peak concentrations of soil Mn(2+) were associated with the reproductive stage of rice growth. Mn(2+) concentrations decreased after drainage of water. In post rice soils, Mn(2+) remained elevated for some time (lag phase), and then rapidly declined. Regression analysis revealed that the process of oxidation of Mn(2+) to Mn(4+) following water drainage decreased with soil depth.

Root exudates contain numerous biologically active low molecular weight secondary metabolites that are produced by plants. Due to their physical and biochemical properties, they are able to interact with many diverse targets in subcellular locations to elicit various activities in microbes, plants and animals. We present specific examples of two families of bioactive secondary plant products which have been well documented as allelochemicals and discuss their production and transport in the plants which produce them and their respective roles in the rhizosphere. We focus on flavonoids which play important roles in the transport of auxin, root and shoot development, pollination, modulation of reactive oxygen species and signalling of symbiotic bacteria in the legume Rhizobium symbiosis. In addition, they possess antibacterial, antifungal, antiviral and anticancer activities. Flavonoids are transported within and between plant tissues and cells by specific transport proteins or transporters and are released into the rhizosphere by roots where they are involved in numerous interactions including allelopathy. Released by root exudation or tissue degradation over time, both aglycones and glycosides of flavonoids and other bioactive secondary metabolites are found in soil solutions and the rhizosphere. We describe their activity and fate in the soil rhizosphere in selected examples involving legumes. Long-chain hydroquinones, in contrast, are lipophilic molecules that are released by passive exudation from living Sorghum spp. root hairs and are involved in allelopathic interactions and in chemical signalling causing stimulation of germination by Striga spp. They are also thought to be involved in nematicidal activity associated with Sorghum haplotypes and are antibacterial to certain soil bacteria. Hydroquinones including sorgoleone are released continuously through pores in the tips of root hairs where they bind to soil particles and organic matter. Once exuded, sorgoleone and its metabolites remain bioactive in the rhizosphere for several days after introduction to living soils. We also discuss the potential for future research to further elucidate the role of secondary metabolites and their fate in the soil rhizosphere.

Research was conducted in 1996 and 1997 at the Horticulture Research Farm in Lexington, KY, to evaluate full season weed control and phytotoxicity for rates of sulfentrazone alone and in combination with Gallery (0.55 kg ai/ha) (0.49 lb ai/A), Treflan (2.18 kg ai/ha) (1.94 lb ai/A), and Pennant (3.27 kg ai/ha) (2.92 lb ai/A). In general, by 12 WAT, control provided by all treatments was only fair to moderate. The greatest reductions in weed cover were observed with the high rate of sulfentrazone (0.55 kg/ha) (0.49 lb ai/A), the combination of sulfentrazone (0.41 kg/ha) (0.37 lb ai/A) plus Pennant, and combinations of sulfentrazone plus Treflan. In all cases, weed control was improved with the use of a higher rate of sulfentrazone, and not necessarily associated with the presence of the partner herbicides. Phytotoxicity was mainly associated with contact of the herbicide with developing foliage, but sulfentrazone was particularly damaging to the herbaceous species Liriope and Hemerocallis, where damage was observed throughout the plants. Sulfentrazone was present in all cases where plants exhibited severe phytotoxicity in response to herbicide treatment. The most sensitive species evaluated in this study were: Abies, Liriope, and Hemerocallis. The most tolerant species included: Fraxinus, Crataegus, and Euonymus. Postemergence directed applications or shielded preemergence applications of sulfentrazone were recommended to possibly decrease phytotoxicity to sensitive species.

The root exudates produced by sorghums contain a biologically active constituent known as sorgoleone. Seven sorghum accessions were evaluated for their exudate components. Except for johnsongrass, which yielded 14.8 mg root exudate/g fresh root wt, sorghum accessions consistently yielded approximately 2 mg root exudate/g fresh root wt. Exudates contained four to six major components, with sorgoleone being the major component (> 85%). Three-dimensional structure analysis was performed to further characterize sorgoleone's mode of action. These studies indicated that sorgoleone required about half the amount of free energy (493.8 kcal/mol) compared to plastoquinone (895.3 kcal/mol) to dock into the QB-binding site of the photosystem II complex of higher plants. Light, cryo-scanning, and transmission electron microscopy were utilized in an attempt to identify the cellular location of root exudate production. From the ultrastructure analysis, it is clear that exudate is being produced in the root hairs and bei...

Crop allelopathy has seldom been used effectively by farmers in weed management. Traditional breeding methods have not been successful in producing highly allelopathic crops with good yields. Genetic engineering may have the potential for overcoming this impasse. Crops have been made resistant to insects, pathogens, and herbicides with transgenes, but biotechnology has not produced crops that control weeds with allelochemicals. The strategies for producing allelopathic crops by biotechnology are relatively complex, usually involving multiple genes. One can choose to enhance production of allelochemicals already present in a crop or to impart the production of new compounds. The first strategy involves identification of the allelochemical(s), determination of the enzymes and genes encoding them, and the use of genetic engineering to enhance their production. The latter strategy employs altering existing biochemical pathways by insertions of transgenes to produce new allelochemicals. With either strategy, t...

Summary Sorghum bicolor (L.) Moensch and other related Sorghum species produce sorgoleone-a long chain hydroquinone compound (MW = 358), which is exuded by living root systems. This compound exhibits potent activity as a photosynthetic inhibitor. A diverse group of sorghum germplasm was evaluated for sorgoleone production. Production was quite variable, with certain accessions producing up to 15 mg sorgoleone/g fresh root weight. The root exudate composition among accessions was less variable, with sorgoleone being the major constituent (76-99%) within the extract. The potential binding of sorgoleone to the D1 protein of the PSII complex was evaluated in triazine resistant and susceptible redroot pigweed (Amaranthus retroflexus L.) thylakoids. Sorgoleone, metribuzin and diuron exhibited competitive binding with atrazine in susceptible thylakoids, while no competition was evident in resistant thylakoids. Sorgoleone has an intermediate affinity between that of diuron and metribuzin from estimated binding co...

Photosensitivity in animals is defined as a severe dermatitis that results from a heightened reactivity of skin cells and associated dermal tissues upon their exposure to sunlight, following ingestion or contact with UV reactive secondary plant products. Photosensitivity occurs in animal cells as a reaction that is mediated by a light absorbing molecule, specifically in this case a plant-produced metabolite that is heterocyclic or polyphenolic. In sensitive animals, this reaction is most severe in non-pigmented skin which has the least protection from UV or visible light exposure. Photosensitization in a biological system such as the epidermis is an oxidative or other chemical change in a molecule in response to light-induced excitation of endogenous or exogenously-delivered molecules within the tissue. Photo-oxidation can also occur in the plant itself, resulting in the generation of reactive oxygen species, free radical damage and eventual DNA degradation. Similar cellular changes occur in affected herbivores and are associated with an accumulation of photodynamic molecules in the affected dermal tissues or circulatory system of the herbivore. Recent advances in our ability to identify and detect secondary products at trace levels in the plant and surrounding environment, or in organisms that ingest plants, have provided additional evidence for the role of secondary metabolites in photosensitization of grazing herbivores. This review outlines the role of unique secondary products produced by higher plants in the animal photosensitization process, describes their chemistry and localization in the plant as well as impacts of the environment upon their production, discusses their direct and indirect effects on associated animal systems and presents several examples of well-characterized plant photosensitization in animal systems.

One concern often voiced by researchers of allelopathic interactions is that many laboratory bioassays do not adequately predict the responses observed in field situations. The questions that arise are: (1) What criteria should be implemented to design ecologically relevant bioassays? (2) What species (crops or weeds) are involved in the interaction? (3) Are we investigating allelopathy of debris/residues or interactions involving living plants? (4) Which plant indicator species are actually cohabiting with the species under investigation? and (5) What are appropriate experimental controls? It is difficult to design a bioassay that can be used to examine responses in all species. In fact, each bioassay must be designed specifically to assess species interactions after careful consideration of growth habit, biotic characteristics, and ecophysiological factors. The objective of this paper is to discuss the significance of bioassays designed to study a particular aspect of allelopathy. We conclude that through a laboratory bioassay we can not demonstrate that allelopathy is operational in natural settings. An investigator should consider allelopathy as one component in a multifaceted approach to ecology and address key questions to determine the relevance of a particular assay. Due to the complexity of field interactions and responses, one can only hope to predict and describe some of the cause-and-effect relationships observed in a field setting. An accurate assessment of these main effects will prove invaluable in directing the focus of future research emphasis.

A reversed-phase HPLC method useful for the analysis of the grapevine phytoalexins resveratrol, its β-d-glucoside, e-viniferin, and pterostilbene in leaf extracts was developed by coupling diode array detection and fluorometry. Phytoalexins were extracted from UV-irradiated grapevine leaves with methanol/water (80:20) and prepurified on C18 solid phase extraction cartridges. Separation by HPLC was achieved using a C18 column and a gradient elution with acetonitrile and water (from 10 to 85% acetonitrile). Analyses of grapevine leaf extracts were performed by injecting the equivalent of 1 mg of leaf fresh weight. Recovery was nearly 100% for the three stilbenes resveratrol, pterostilbene, and e-viniferin (ranging from 100.2 to 104.8%), and replicate analyses gave coefficients of variation of 0.6−2.5%. Identification of each phytoalexin was accomplished by line spectral comparisons with known standards, and e-viniferin was further characterized by MS and GC/MS. Simultaneously, stilbenes were detected by flu...

Effects of the alleochemical sorgoleone on photosynthetic electron transport by oxygen-evolving chloroplast thylakoids and Triton X-100-prepared Photosystem II (PSII) membranes were analyzed. The Hill activity of the thylakoids proved to be at least as sensitive to inhibition by sorgoleone as it was to DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea], a potent herbicidal inhibitor of PSII. However, a Photosystem I (PSI) partial reaction was not affected by a 10-fold greater concentration of sorgoleone than is required for complete inhibition of Hill activity. Measurements of flash-induced chlorophyll a variable fluorescence showed that sorgoleone neither dissipated excitation energy nor diminished the amplitude of chlorophyll a variable fluorescence. However, it inhibited the decay of variable fluorescence as effectively as DCMU, which blocks the oxidation of the PSII-reduced primary electron acceptor, Q-A, by the PSII secondary electron acceptor, QB, by displacing QB from the D1 protein. Additionally, sorg...

Biorational alternatives are gaining increased attention for weed control because of concerns related to pesticide usage and dwindling numbers of labeled products, particularly for minor-use crops. Allelopathy offers potential for biorational weed control through the production and release of allelochemics from leaves, flowers, seeds, stems, and roots of living or decomposing plant materials. Under appropriate conditions, allelochemics may be released in quantities suppressive to developing weed seedlings. Allelochemics often exhibit selectivity, similar to synthetic herbicides. Two main approaches have been investigated for allelopathic weed suppression. One is use of living rotational crops or mulches that interfere with the growth of surrounding weeds [e.g., tall red fescue, Festuca arundinacea Schreb.; creeping red fescue, F. rubra L. subsp. commutata; asparagus, Asparagus officinalis L. var. altilis); sorghum, Sorghum bicolor (L.) Moench; alfalfa, Medicago saliva L.; black mustard, Brassica nigra (L.) Koch; and oat, Avena saliva L.]. Attempts to select germplasm with enhanced suppressive ability have been limited. The second is use of cover crop residues or living mulches to suppress weed growth for variable lengths of time (e.g., winter rye, Secale cereale L.; winter wheat, Triticum aestivum L.; and sorghum). Cover crop residues may selectively provide weed suppression through their physical presence on the soil surface and by release of allelochemics or microbially altered allelochemics. The ability to understand the physiological basis for allelopathy in a crop plant may allow the weed scientist or ecologist to work closely with molecular biologists or traditional plant breeders to selectively enhance the traits responsible for weed suppression.

Bioassays using binary mixtures that included a cover crop with known allelopathic potential and a weed species were employed to determine the importance of allelopathy compared to resource competition as interference mechanisms. Responses of weed species germinated with cover crops in a petri dish were measured. Interference between weed and cover crop seedlings was determined in a greenhouse experiment using the additive design, which included partitions to reduce above- and below-ground competition and used capillary mat subirrigation to control moisture and fertilizer availability. Germinating sorghum reduced radicle length of weeds, whereas germinating rye tended to increase weed radicle length. Methods limited above-ground competition, so likely interference mechanisms were below-ground competition and allelopathy. Germination with a cover crop had little effect on germination and shoot length of weeds. Increased density of rye but not of sorghum reduced growth of barnyardgrass seedlings. Reduced number of barnyardgrass leaves in the presence of rye was likely due to allelopathy. Suppression of barnyardgrass dry weight attributed to allelopathic interference by rye was successfully separated and compared to the combined effects of competition and allelopathy.

Sweet corn and pumpkin were planted no-tillage (NT) into cover crop residue treatments of vetch, rye, crimson clover, and ladino clover controlled with glyphosate, and a bare ground conventional tillage (CT) control. Objectives included evaluation of crop growth, yield, and weed suppression in NT versus CT treatments. Herbicide application was also investigated, with a plus and minus herbicide treatment (alachlor plus cyanazine for sweet corn, or ethalfluralin for pumpkin) as the main factor in the factorial experiment, and cover crops the subfactors. Weed control 4 wk after planting was dependent upon cover crop. The fewest weed numbers and least biomass were found in the ladino clover plots, but clover regrowth and subsequent competition with the cash crop were severe. Herbicides also affected weed biomass at 4 wk after vegetable planting, with least biomass in herbicide-treated plots. Neither cover crop nor herbicide treatment significantly affected weed weight by 8 wk after planting or pumpkin fruit weight at harvest. Pumpkin yield was not influenced by herbicide application. The vetch cover, although harboring greatest weed biomass, produced the greatest total yield (ear weight) in sweet corn. When averaged over cover crop, sweet corn yields were higher in herbicide-treated plots than in untreated ones. Both sweet corn and pumpkin maturity were generally delayed in the absence of herbicide treatments or in the presence of cover crop residues, especially clover and rye residues.

Greenhouse experiments that used capillary mat subirrigation to maintain constant soil moisture and to sup- ply fertilizer continuously were conducted to evaluate the effects of sorghum or rye residue on early growth of barn- yardgrass and velvetleaf. The separate effects of root residue and of shoot residue were compared to the combined effects of root plus shoot residues and to an uncovered soil control. Residues included as nontoxic controls were leached shoot tissue and poplar excelsior. Shoot residue, leached shoot tissue, and poplar excelsior were surface-applied on an equal light transmittance basis such that mass of poplar excelsior > shoot residue > leached shoot tissue. The presence of rye root residue delayed emergence of barnyardgrass. Surface- applied residues tended to decrease barnyardgrass height, but velvetleaf stem length was greater in treatments with surface residue. Although cover crop shoot residues had little effect on weed growth after 18 d, weed growth decreased in the presence of cover crop root residues and poplar excel- sior. Nomenclature: Barnyardgrass, Echinochloa crus-galli L. #3 ECHCG; velvetleaf, Abutilon theophrasti Medicus # ABUTH; rye, Secale cereale L. 'Wheeler'; sorghum, Sor- ghum bicolor (L.) Moench 'Pioneer Hybrid #8333.' Additional index words. Capillary mat subirrigation, cover crop, alielopathy, physical effects.

Inhibition of photosynthetic electron transport in isolated spinach ( Spinacea oleracea L.) thylakoids and competitive binding to spinach, redroot pigweed ( Amaranthus retroflexus L.), and potato ( Solanum tuberosum L.) thylakoids were investigated for sorgoleone (2-hydroxy-5-methoxy-3-[(8′Z, 11′Z)-8′,11′,14′-pentadecatriene]- p -hydroquinone) in comparison with other photosystem II inhibitors. Sorgoleone inhibited photosynthetic electron transport as effectively as DCMU (diuron) [ N ′-(3,4-dichlorophenyl)- N,N -dimethylurea]. Rapid inhibition was observed by both compounds at concentrations of less than 0.2 μ M. Sorgoleone competed with atrazine [6-chloro- N -ethyl- N′ -(1-methylethyl)-1,3,5-triazine-2,4-diamine] for binding to spinach, triazine-susceptible redroot pigweed or potato thylakoids as effectively as metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazine-5(4H)-one] or diuron. No competition was observed for bentazon [3-(methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Double reciprocal plots in the presence or absence of 0.5 μ M sorgoleone showed that sorgoleone is a competitive inhibitor of atrazine. Competitive binding was not observed in atrazine-resistant redroot pigweed or potato thylakoids. We conclude that sorgoleone is a potent inhibitor of photosynthetic electron transport and binds to the same Q B niche of the D1 protein as diuron, atrazine, or metribuzin.

The relative phytotoxicity of sorgoleone as measured by seed germination and seedling growth of selected crop and weed species and inhibition of photosynthetic oxygen evolution in atrazine-resistan...

Flavonoids are biologically active low molecular weight secondary metabolites that are produced by plants, with over 10,000 structural variants now reported. Due to their physical and biochemical properties, they interact with many diverse targets in subcellular locations to elicit various activities in microbes, plants, and animals. In plants, flavonoids play important roles in transport of auxin, root and shoot development, pollination, modulation of reactive oxygen species, and signalling of symbiotic bacteria in the legume Rhizobium symbiosis. In addition, they possess antibacterial, antifungal, antiviral, and anticancer activities. In the plant, flavonoids are transported within and between plant tissues and cells, and are specifically released into the rhizosphere by roots where they are involved in plant/plant interactions or allelopathy. Released by root exudation or tissue degradation over time, both aglycones and glycosides of flavonoids are found in soil solutions and root exudates. Although the relative role of flavonoids in allelopathic interference has been less well-characterized than that of some secondary metabolites, we present classic examples of their involvement in autotoxicity and allelopathy. We also describe their activity and fate in the soil rhizosphere in selected examples involving pasture legumes, cereal crops, and ferns. Potential research directions for further elucidation of the specific role of flavonoids in soil rhizosphere interactions are considered.

Sorghum allelopathy has been reported in a series of field experiments following sorghum establishment. In recent years, sorghum phytotoxicity and allelopathic interference also have been well-described in greenhouse and laboratory settings. Observations of allelopathy have occurred in diverse locations and with various sorghum plant parts. Phytotoxicity has been reported when sorghum was incorporated into the soil as a green manure, when residues remained on the soil surface in reduced tillage settings, or when sorghum was cultivated as a crop in managed fields. Allelochemicals present in sorghum tissues have varied with plant part, age, and cultivar evaluated. A diverse group of sorghum allelochemicals, including numerous phenolics, a cyanogenic glycoside (dhurrin), and a hydrophobic p-benzoquinone (sorgoleone) have been isolated and identified in recent years from sorghum shoots, roots, and root exudates, as our capacity to analyze and identify complex secondary products in trace quantities in the plant and in the soil rhizosphere has improved. These allelochemicals, particularly sorgoleone, have been widely investigated in terms of their mode(s) of action, specific activity and selectivity, release into the rhizosphere, and uptake and translocation into sensitive indicator species. Both genetics and environment have been shown to influence sorgoleone production and expression of genes involved in sorgoleone biosynthesis. In the soil rhizosphere, sorgoleone is released continuously by living root hairs where it accumulates in significant concentrations around its roots. Further experimentation designed to study the regulation of sorgoleone production by living sorghum root hairs may result in increased capacity to utilize sorghum cover crops more effectively for suppression of germinating weed seedlings, in a manner similar to that of soil-applied preemergent herbicides like trifluralin.

Research was conducted during 1990 and 1991 at the Horticultural Research Farm in Lexington, Kentucky, to evaluate the efficacy of herbicides available for use on woody landscape plants (simazine and oryzalin), newly labelled herbicides (isoxaben, isoxaben plus oryzalin, metolachlor and metolachlor plus simazine) and those not widely labelled for the nursery industry (oxyfluorfen and dithiopyr). Herbicide phytotoxicity was also evaluated in 10 species of woody nursery crops. Results 6 WAT (weeks after treatment) indicated that the standard of simazine at 1.1 kg ai/ha (1.0 lb/A) plus oryzalin at 3.3 kg ai/ha (3.0 lb/A) provided adequate control of most common broadleaf weeds (98%) and annual grasses (98%) but not yellow nutsedge (31%). Isoxaben plus oryzalin at 4.2 kg ai/ha (4.0 lb/A) (DF formulation) and isoxaben plus trifluralin at 4.2 kg ai/ha (4.0 lb/A) (granular formulation) gave excellent full-season control of nearly all broadleaf and grass weeds with the exception of galinsoga and field bindweed. In addition, yellow nutsedge control was acceptable, ranging from 63 to 96% in these treatments. Isoxaben alone also provided excellent broadleaf control (93%) 6 WAT in 1990 but poorer (

Post-rice irrigated soils offer several potential advantages for the growth of subsequent crops, but Australian producers have often been reluctant to grow grain legumes immediately following a rice crop due to physico-chemical constraints. A field experiment was thus conducted to explore the potential for producing grain legumes following rice in comparison to those following a fallow during 2012 and 2013. Two grain legumes, field pea and faba bean, were sown 5, 7 and 12 weeks after rice harvest in 2013 at Yanco, NSW, and plant growth indicators and grain yield were compared. Early sowing of field pea following rice gave the best outcome, with plants flowering three weeks earlier and yielding 1330 kg·ha−1 more grain than after fallow. In contrast, faba bean yield was 35 kg·ha−1 less after rice than after fallow across the three sowing dates. Higher pea yield was consistent with the early emergence of seedlings, higher light interception and overall greater plant growth following rice. Post-rice crops also had 10-fold less weed infestation than crops in a similarly-established fallow treatment and, thus, required far less weed management. Legume crops sown at the later seeding date had significantly reduced (~50%–60%) yields compared to those of the first two sowings; this is most likely a reflection of reduced temperatures and day lengths experienced during vegetative and reproductive growth phases.

The development of genetic profiles of invading plants can provide insight towards a better understanding of niche utilization. Recent advances in sequencing techniques have greatly facilitated genetic assessment and profiling. Here we review our recent studies on selected Australian Cucurbitaceae and Boraginaceae to demonstrate the application of genetic sequencing across a selection of invasive Australian plants., Part of the challenge in dealing with invasive plant species is that they seldom represent a uniform, static entity. Often, an accurate understanding of the history of plant introduction and knowledge of the real levels of genetic diversity present in species and populations of importance is lacking. Currently, the role of genetic diversity in promoting the successful establishment of invasive plants is not well defined. Genetic profiling of invasive plants should enhance our understanding of the dynamics of colonization in the invaded range. Recent advances in DNA sequencing technology have greatly facilitated the rapid and complete assessment of plant population genetics. Here, we apply our current understanding of the genetics and ecophysiology of plant invasions to recent work on Australian plant invaders from the Cucurbitaceae and Boraginaceae. The Cucurbitaceae study showed that both prickly paddy melon (Cucumis myriocarpus) and camel melon (Citrullus lanatus) were represented by only a single genotype in Australia, implying that each was probably introduced as a single introduction event. In contrast, a third invasive melon, Citrullus colocynthis, possessed a moderate level of genetic diversity in Australia and was potentially introduced to the continent at least twice. The Boraginaceae study demonstrated the value of comparing two similar congeneric species; one, Echium plantagineum, is highly invasive and genetically diverse, whereas the other, Echium vulgare, exhibits less genetic diversity and occupies a more limited ecological niche. Sequence analysis provided precise identification of invasive plant species, as well as information on genetic diversity and phylogeographic history. Improved sequencing technologies will continue to allow greater resolution of genetic relationships among invasive plant populations, thereby potentially improving our ability to predict the impact of these relationships upon future spread and better manage invaders possessing potentially diverse biotypes and exhibiting diverse breeding systems, life histories and invasion histories.

A reduced-till (RT) experiment determined the effect of rye seeding density and method of kill on rye biomass persistence, weed suppression, and tomato yield. ‘Wheeler’ rye was seeded at 56, 110, and 170 kg ha−1in the fall of 1988 and 1989 in Champaign, IL; Lexington, KY; and Lafayette, IN. One wk before transplanting tomatoes, rye was desiccated either by applying glyphosate at 1.1 kg ha−1and mowing (RT-glyphosate) or by mowing alone (RT-mowed). Both methods left rye residues on the soil surface as a mulch. Seeding density did not affect rye biomass, weed control, or tomato yield. Rye biomass differed depending on location and year, ranging from 320 to 1150 gm−2. Rye was completely killed by glyphosate, but regrew following mowing. RT-glyphosate suppressed weeds for 4 to 8 wk, which was similar to the suppression from conventional tillage (fall plowing with spring disking and harrowing) with trifluralin and metribuzin (CT-herbicide). Weed communities varied, but redroot pigweed and giant foxtail were present at all three locations. All treatments required supplemental weed management for commercially acceptable control. Except for IL in 1990, processing tomato yields (kg ha−1) in RT-glyphosate with hand-weeding were equal or better than yields in the CT treatments.

Experiments were conducted at Lexington and Quicksand, KY, in 1989 and 1990 to determine the effect of preplant incorporated clomazone on weed control, crop in- jury, and yield of broccoli, cauliflower, green cabbage, red cabbage, and pak choi. Oxyfluorfen and trifluralin were included as standard treatments. Greater than 80% weed control was observed at both locations with 0.8 kg ai ha-1 clomazone, with the exception of smooth pigweed at Lex- ington. All clomazone treatments caused crop injury 2 WAT. Injury was still evident 8 WAT at clomazone rates of 1.7 and 3.4 kg ha-', but was minor with rates of 0.8 kg ha-' or less on broccoli, cauliflower, and red cabbage. Injury was less at Quicksand in both years and seasons over all clomazone rates, most likely due to higher soil organic matter content Yields of broccoli and cauliflower treated with 0.8 kg ha-1 clomazone were similar to yields with oxyfluorfen on a 3 % organic matter soil at Lexington in 1989. However, cloma- zone at 0.8 kg ha-' at Lexington reduced 1989 spring yields of green cabbage, red cabbage, and pak choi and 1990 spring yields of all cole crops as compared to oxyfluorfen. Cloma- zone at 0.8 kg ha-1 at Quicksand reduced yield of green cabbage and pak choi in spring 1990 only on a 5.2% organic matter soil. Fall yields of broccoli and cauliflower in both years were not reduced by clomazone at 0.8 kg ha-1 or less at either location. Our studies indicated potential for utilization of clomazone on cole crops in higher organic matter soils, especially if some early season crop injury and occasional yield loss can be tolerated. Nomenclature: Clomazone, 2-((2- chlorophenyl)methyl)-4,4-dimethyl-3-isoxazolidinone; oxy- fluorfen, 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4- (trifluoromethyl)benzene; trifluralin, 2,6-dinitro-N,N- dipropyl4-(trifluoromethyl)benzenamine; smooth pigweed, Amaranthus hybridus L. #3 AMACH; cole crops, Brassica oleracea L. broccoli, 'Green Comet,' cauliflower, 'Snow Crown,' green cabbage, 'Bravo,' red cabbage, 'Solid Red hybrid 781,' pak choi, Brassica campestris L. 'Joy Choi.' Additional index words. Selectivity, dimethazone, crop injury.

Camel melon (Citrullus lanatus), colocynth (Citrullus colocynthis) and prickly paddy melon (Cucumis myriocarpus) are summer-growing invasive weeds distributed throughout Australia. We used DNA-sequence information from samples collected across Australia and morphological data from glasshouse-grown plants to determine diagnostic features of these species, and to determine the infraspecific identity of Australian Citrullus lanatus and Cucumis myriocarpus. All species possessed distinct genotypes and haplotypes at nuclear G3pdh and chloroplast ycf6–psbM gene regions and could be easily identified on the basis of molecular phylogenetic analysis. A combination of vegetative, floral, fruit and seed characters also allowed for species identification at all developmental stages. On the basis of our morphological and molecular analyses, Australian camel melon and prickly paddy melon populations were identified as Citrullus lanatus var. citroides and Cucumis myriocarpus subsp. myriocarpus respectively.

Laboratory assays were conducted to determine the sensitivity of tomato and tobacco cell suspension cultures and tomato and pepper cotyledons to clomazone. A comparison of fresh weight and carotenoid content indicated up to a three-fold difference between the clomazone-tolerant to- bacco and clomazone-susceptible tomato cell suspension cul- tures. In contrast, an approximate 60-fold difference between the tolerant pepper and susceptible tomato cotyledons was observed when total chlorophyll and carotenoid contents were measured. The effect of clomazone and its possible metabolites on in vivo and in vitro extractable IPPisomerase (EC 53.3.2) and prenyl transferase (EC 2.5.1.29) activity was investigated. There was no clear inhibitory effect of cloma- zone or possible clomazone metabolites upon enzyme activity in tomato or tobacco cell suspension cultures or on light or dark grown tomato or pepper cotyledons. No specific enzy- matic target site of clomazone was identified in correlation with the reduction in total chlorophyll or carotenoid content. Nomenclature: Clomazone, 2-((2-chlorophenyl)methyl)-4,4- dimethyl-3-isoxazolidinone; pepper, Capsicum annum L. cv Yolo Wonder L; tobacco, Nicotiana tabacum L. 'KY-14'; tomato, Lycopersicon esculentum Mill. 'Niagara.'

Physiological factors involved in seed dormancy in Cucumis sativus var. hardwickii (Royle) Alef. were investigated. Hardwickii seed (PI 183967) demonstrated a dormancy which required 100 days of after-ripening under ambient temperature (25°C) and humidity (approx. 60%) for 50% germination (T50). Removal of the seed coat released hardwickii embryos from dormancy and permitted 100% germination. Increasing the relative humidity above 60% in the atmosphere surrounding seeds stored at 25°C decreased the after-ripening time for T50 to between 42 and 56 days. After-ripening at 37 or 47°C reduced the T50 to 75 days, in comparison to a T50 of more than 100 days for temperatures below 37°C. When germinated on solutions of increasing osmolarities of polyethyleneglycol 4000, isolated embryos given longest after-ripening treatments had the greatest growth potential. Solvent extracts of dormant hardwickii seed were evaluated for inhibitors of germination in cucumber and curly cress bioassays. Seed dormancy in hardwickii is most likely not attributable to inhibitors present within hardwickii seed. It is hypothesized that after-ripening increases the growth potential of the embryo by allowing radicle penetration of the seed coat which may present a significant physical barrier in dormant seeds.

A laboratory bioassay was conducted to determine the differential tolerance of cole crops to clomazone as measured by extractable total chlorophyll and carotenoids. Clomazone concentrations causing 50% inhibition (I50) in the biosynthesis of total chlorophyll in broccoli, cauliflower, and green and red cabbage cotyledons were 16, 11, 3, and 11 μM, respectively, while I50values for carotenoid levels were 20, 10, 4, and 8 μM clomazone, respectively. Therefore, broccoli was the most tolerant to clomazone based upon extractable chlorophyll and carotenoid concentrations. Further laboratory studies were performed to investigate the basis for differential clomazone tolerance in 3-wk-old cole crop seedlings. No differences in total root uptake of14C-clomazone were observed between these crops after 24 h. There were no differences in rate of metabolism of14C-clomazone to methanol-soluble metabolites in roots of these crops. Percentage of polar metabolites in roots remained fairly constant over time. There were also no differences between crops in percentage of methanol-soluble14C-clomazone metabolites formed in shoots between 24 and 96 h. In all crops, levels of14C-clomazone decreased in a similar manner over time in methanolic extracts of roots and shoots while nonextractable14C levels increased, indicating a conversion of clomazone to insoluble, nonextractable forms. Differential uptake, translocation, and metabolism do not appear to account for clomazone selectivity differences between cole crop seedlings.

The U.S. cucumber germplasm collection (753 accessions) and U.S. adapted processing cucumber (Cucumis sativus L.) inbreds and hybrids were surveyed for response to 6.7 kg ae/ha of chloramben. Nine plant introductions (PI 165952, 173892, 179676, 275411, 277741, 279464, 279465, 436609, and 482464) were classified as tolerant to chloramben, based on percentage and rate of field emergence and seedling vigor. All adapted strains evaluated were susceptible to chloramben injury. The chloramben-tolerant accessions (C0) were subjected to two cycles of recurrent half-sib family selection that resulted in 11 C2 families. These families, a susceptible adapted line (WI 2870), and the resistant PI 436609 were evaluated in the field (6.7 kg ae/ha) and laboratory (0.0, 0.01, and 0.0001 M) for response to chloramben challenge. Significant (P = 0.05) differences between families were observed for percentage emergence and phytotoxicity ratings. Correlations between emergence and phytotoxicity ratings at two dates were low (r2 = -0.32 and – 0.05). Significant (P = 0.05) interfamily differences were also recorded for percentage germination, hypocotyl length, primary root length, and number of lateral roots in the laboratory. Correlated responses between these growth variables were high (r2 = 0.78 to 0.84), but correlations between field and laboratory observations were low (r2 = -0.31 to 0.24). We hypothesize that the genetic response to chloramben challenge under laboratory conditions depends on the concentration of the chemical administered. Chemical name used: 3-amino-2, 5-dichlorobenzoic acid (chloramben).

Black and pale swallow-worts are invasive perennial vines that were introduced 100 years ago into North America. Their invasion has been centralized in New York State, with neighboring regions of southern Canada and New England also affected. The two species have typically been more problematic in natural areas, but are increasingly impacting agronomic systems such as horticultural nurseries, perennial field crops, and pasturelands. While much of the literature reviewed herein is focused on the biology and management of the swallow-worts, conclusions are also presented from research assessing the ecological interactions that occur within communities invaded by the swallow-wort species. In particular, we posit that the role of allelopathy and the relationship between genetic diversity levels and environmental characteristics could be significant in explaining the aggressive nature of swallow-wort invasion in New York. Findings from the literature suggest that the alteration of community-level interactions by invasive species, in this case the swallow-worts, could play a significant role in the invasion process.

The recent emphasis on development of alternative, non-chemical weed strategies for landscape and roadside management has led to the study and utilization of well-adapted landscape groundcovers, including turfgrass and herbaceous ornamentals that can successfully withstand and suppress weed invasion. By selecting groundcovers which exhibit growth characteristics that result in consistent interference with weed establishment, one can successfully achieve effective long-term weed control in the landscape using reduced herbicide and labor inputs. In addition to allelopathic characteristics resulting in enhanced weed suppression due to the production and release of phytoinhibitors in the landscape, some groundcovers effectively suppress weedy invaders through competition for space, sunlight, moisture, nutrients and even direct alteration of the rhizosphere environment. Additional information related to weed biology and the impact of cultural practices used in the landscape on weed infestation are also critical when considering long-term and sustainable weed suppression for landscape and natural settings. Until recently, little information was available regarding the development of low maintenance landscapes for use in the Northeastern United States, with the exception of roadside trials documenting utilization of certain direct-seeded groundcovers in highway medians. Recent studies in both landscape and roadside settings have indicated that the selection and utilization of certain herbaceous perennial groundcovers and turfgrasses may not only result in lower labor inputs with respect to maintenance, they may further prevent the spread of noxious invasive weeds by severely limiting their ability to establish. When surveyed, stakeholders reported that weed suppressive groundcovers had much greater aesthetic appeal than those that were partially infested. Many of these groundcovers suppress weeds effectively by intense competition for resources, particularly by reduction in the amount of available light at the soil surface due to dense canopy cover. In addition, some groundcovers such as Nepeta x faasennii and Festuca rubra inhibit weed seedlings by their potential release of allelochemicals into the rhizosphere. Although still relatively novel, allelopathic groundcovers and turfgrasses offer interesting possibilities for future development of allelochemicals as bioherbicides and attractive, stress-tolerant and pest-resistant landscape plantings.

The establishment and management of nine cover crops in Kentucky production systems were evaluated in field experiments over a 2.yr period. 'Wheeler' rye, 'Barsoy' barley, and 'Tyler' wheat cereal grains produced greater biomass (180 to 260 g/m2) than the pasture species tall fescue, creeping red fescue, and white clover (55 to 110 g/m2). 'Kentucky 31' tall fescue, creeping red fescue, and white clover proved most difficult to control, and significant regrowth occurred regardless of herbicide or rate applied. HOE-39866 (1.7 kg ai/ha) was effective in rapidly controlling all cover crops except tall fescue by 30 days after application. Sethoxydim and fluazifop (0.4 and 0.3 kg ai/ha, respec- tively) effectively controlled the cereals and two ryegrass species. Glyphosate applied at 1.1 and 2.2 kg ai/ha was also effective, while 0.6 kg ai/ha controlled only cereal grain growth adequately. After chemical control, pasture grass plots contained fewest weeds/m2 with some reduc- tions likely due to density and regrowth of the sods. Cover crops were effective in suppressing weed growth at 45 days after chemical control. However, significant weed growth existed in all cover crop plots by 60 days after kill. Row crop establishment increased linearly with increasing glyphosate rate. Cereal grain covers provided the most compatible planting situations for greatest seedling estab- lishment, with rye and wheat providing greatest weed suppression. Generally, increased weed suppression pro- vided by a cover crop was accompanied by reduced row crop establishment, with greatest reductions observed in pasture grass plots. Cucumber was most easily established while snap pea was most difficult. Nomenclature: Fluazi- fop, (?)-2-(4-((5-(trifluoromethyl)-2-pyridinylloxy)phen- oxy)propanoic acid; HOE-39866, the ammonium salt of DL-homoalanin-4-yl-methyl phosphinic acid; glyphosate, N-(phosphonomethyl)glycine; sethoxydim, 2-(1-(ethoxyim- ino)butyl - 5 - (2-(ethylthio)propyl) - 3 - hydroxy - 2 - cyc- lohexen-l-one; tall fescue, Festuca arundinacea Schreb. 'Kentucky 31'; creeping red fescue, Festuca rubra L. ssp. commutata; Dutch white clover, Trifolium repens L.; cucumber, Cucumis sativus var. sativus 'Calypso'; snap pea, Pisum sativa L. 'Sparkle'; rye, Secale cereale L. 'Wheeler'; winter wheat, Triticum aestivum L. 'Tyler'. Additional index words. Minimum tillage, germination, glyphosate, sethoxydim, fluazifop, HOE-39866, row crop.

Hypericum perforatum, or St. John’s wort, is currently used medicinally to treat neurological disorders, while research continues to seek practical methods to harness the plant’s proven potential as an anti-cancer and anti-retroviral drug source. More than other medicinal plant preparations, bioactive components of H. perforatum are often found to vary by a factor of two compared to concentrations reported on labels for the prepared drug. Variability is attributable to environmental condition fluctuations to which the plants were exposed during growth and development. Daily light integral control has been shown to produce predictable, consistent biomass gain in other crops, but has not been related yet to secondary metabolite production in H. perforatum. This project focused on production of three important secondary metabolites, hypericin, pseudohypericin and hyperforin, from plants grown in floating hydroponic systems in controlled environments with the light integral held at 8.6, 13 or 20 mol m-2 d-1 and an average light intensity of 340 µmol m-2 s-1 (at 25C, 16 hour photoperiod). Plant growth data and metabolite concentrations (determined by HPLC), from seedling stage to 108 day old plants, are presented. An exponential model for biomass estimation per square meter of growing space is presented, valid between the integrals of 8.6 and 20 mol m-2 d-1, a photosynthetic period of 16 hours, 25C constant air temperature and ambient CO2 concentration.