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Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG Allelopathic activity of wheat (Triticum aestivum L.) has previously been associated with the production of phenolic acids and flavonoids (PAF), benzoxazinones (BXZs) and phenoxazinones (PXZs). The biosynthesis of BXZs is closely regulated during cereal growth, with accumulation highest in young tissues with variation associated with genotype and environmental conditions. This review is focused on BXZ metabolites and their impact on germination, seedling growth and physiological, biochemical, transcriptional and proteome traits of surrounding plants and weeds. The major pathways employed by plants for benzoxazinoid detoxification involve hydroxylation and glucosylation and polymerisation of intermediates in these pathways. Allelochemicals from various wheat genotypes have been shown to inhibit the growth of selected weed species, including Bromus japonicus, Chenopodium album, Portulaca oleracea, Avena fatua and Lolium rigidum. Wheat allelopathy is potentially exploited from the standpoint of crop mulches, incorporation of crop residues, tissue disruption, intercropping with allelopathic cultivars and application of aqueous wheat extracts. BXZs have been shown to suppress the growth and development of certain agricultural pests, including insects, fungal pathogens, and weeds. Many native plants, fungi and insect herbivores inherently possess varying tolerance levels towards BXZs. However, other BXZ- susceptible species are adversely impacted by elevated BXZ levels in crop plants. Thus, considerations for the selection and breeding of wheat genotypes possessing enhanced defensive ability via elevated BXZ contents are discussed. Here, these objectives are reconsidered with a focus on co-evolutionary aspects and their potential impacts on biodiversity in the agroecosystems under study. For future breeding efforts to be successful, it is important to take such potential adverse environmental impacts into account, in combination with an increased focus on enhancing beneficial allelopathic effects within agricultural systems.

Hordeum spp. (barley grass) and Bromus spp. (brome grass) are annual weed species that achieve long‐distance seed dispersal via attachment to sheep, but also lead to sheep carcass damage due to the penetration of seeds into animal tissues. Range expansion of invasive weed populations predicted as a consequence of climate change may be associated with an increase in seed contamination incidence globally. An examination of Australian abattoir data (2006–2012), along with recent weed distribution patterns, indicates carcass contamination was associated with rainfall and abundance of key annual grass weeds, primarily Bromus spp. and Hordeum spp., although other factors may play a contributing role. Significant differences in seed contamination in slaughtered sheep were noted between states and regions, with widespread contamination occurring throughout all agro‐ecological zones. Abattoir, sheep age and sex significantly influenced incidence, with contamination highest in adult males. Incidence increased with mean monthly rainfall, but declined with mean elevation, and significant interactions were noted between mean monthly temperature and state, and between mean elevation and year. Results show the need for vigilant recording of seed injuries in sheep to enhance weed surveillance efforts and effective integrated weed management of contributing annual grass weeds.

Six cycles of recurrent selection for early shoot vigour in wheat resulted in significant increases in leaf width and shoot biomass. Here, in replicated controlled-environment studies, the effect of early shoot vigour on root biomass, rhizosheath size, root hair length, and cell size in the roots and leaves was examined across different cycles of selection. Increased shoot vigour was associated with greater root biomass, larger rhizosheath size, and longer root hairs. Our findings demonstrate that rhizosheath size was a reliable surrogate for root hair length in this germplasm. Examination of the root epidermis revealed that the ‘cell body’ of the trichoblasts (hair-forming cells) and the atrichoblasts (non-hair-forming cells) decreased in size as shoot vigour increased. Therefore, in higher vigour germplasm, longer root hairs emerged from smaller trichoblasts so that total trichoblast volume (root hair plus cell body) was generally similar regardless of shoot vigour. Similarly, the sizes of the four main cell types on the leaf epidermis became progressively smaller as shoot vigour increased, which also increased stomatal density. The relationship between shoot vigour and root traits is considered, and the potential contribution of below-ground root traits to performance and competitiveness of high vigour germplasm is discussed.

Background and objectives: Integrated weed management in commercial wheat production is urgently needed due to increasing herbicide resistance and production costs. Benzoxazinoids (BXs), which include benzoxazinones and benzoxazolinones, are unique bioactive metabolites produced by certain members of the Poaceae including maize, wheat, rye and some dicots. BXs play important roles in plant defence and are causal agents of allelopathic interference. We investigated the role of genetics, environment and crop growth stage on BX abundance in the roots and rhizoplane of selected commercial wheat cultivars, and quantified their microbial transformation products (aminophenoxazinones) in roots and rhizosphere soils. Methods: Cultivar trials of competitive wheat (Triticum aestivum L.) genotypes were conducted in two moderate to low rainfall (449–572 mm) locations in southeastern Australia in 2015 and 2016. Replicated shoot, root, rhizoplane, and rhizosphere soil samples were collected for metabolic profiling at selected crop phenological stages, extracted and further analysed for known benzoxazinoid metabolites by liquid chromatography coupled with high resolution mass spectrometry. Results: Fifteen BXs and related microbially derived aminophenoxazinones were detected in wheat shoots, roots, rhizoplanes and rhizosphere soils in both years and locations. MBOA, HMBOA and HMBOA-Glc were the three most abundant BX metabolites in wheat tissues, with the heritage cultivar Federation producing the highest levels of MBOA. The phytotoxic aminophenoxazinones APO and AMPO were the most abundant BX microbial transformation products and were detected in wheat roots, rhizoplanes and rhizospheres. Abundance varied with cultivar, growth stage, location and year. Conclusions: Microbially-produced aminophenoxazinones generated from both heritage and modern wheat root exudates were detected and quantified in rhizosphere soils, with abundance dependent on cultivar, growth stage, and season. Concentrations of microbial metabolites APO, AMPO, and AAPO were higher in the rhizosphere of young wheat seedlings in contrast to that of mature plants suggesting that phenoxazinone production was upregulated early in the season. Our findings demonstrate that BX metabolites at all life stages of wheat potentially undergo rapid biotransformation to aminophenoxazinones under field conditions, resulting in ecologically relevant concentrations sufficient for weed suppression by certain wheat cultivars.

Weed suppressive potential of annual pasture legumes has been previously described, the mechanism of interference with weeds has not been clearly elucidated. We, therefore, aimed to delineate the role of secondary metabolites synthesized and released by pasture legumes through a series of studies to: 1) characterize key metabolites present in plant tissues, residue and the rhizosphere and 2) correlate their presence with weed suppressive properties. Field and in vitro experimentations coupled with targeted and non-targeted metabolic profiling was performed to evaluate the abundance of key phytotoxic metabolites using UHPLC QTOF-MS. Further, those metabolites strongly correlated with weed suppression and phytotoxicity were predicted by chemometric analyses and their concentration evaluated in field soils collected from the same legume site. Field experimentation, methanolic extracts and dried residues of Biserrula pelecinus L. and Ornithopus compressus L. exhibited marked phytotoxicity in a series of laboratory experiments. Metabolic profiling revealed that both foliar tissues and rhizosphere soils of pasture legumes possessed a high abundance of flavonoids and their precursors. Chemometric analyses suggested the strong association of quercetin, isoquercetin, kaempferol, and kaempferol-7-O-glucoside with weed suppression under field conditions. Specifically, the abundance of quercetin and kaempferol was significantly higher in soils collected from established stands of biserrula and yellow serradella in contrast to arrowleaf, gland and subterranean clover. Current study provided an evidence for the role of certain annual legume-produced flavonoids in weed suppression in southern Australia and further insight into their localization and release in the soil rhizosphere.

Amaranthus retroflexus L., an introduced invasive weed in southern Australia, has been associated with acute renal failure and/or mortality in a number of livestock species. While its leaves, flowers and stems are generally reported to contain high levels of nitrogen, few studies have fully characterised the chemical composition of A. retroflexus foliage with respect to mammalian toxicity. We performed extensive metabolic profiling of stems, leaves, roots and inflorescence tissues of A. retroflexus collected from three spatially and/or temporally distinct toxicity outbreaks, and report on the 1) composition of primary and secondary metabolites in methanolic extracts of A. retroflexus tissues using HPLC and HPLC-MS QToF and 2) chemometric analysis of A. retroflexus extracts in relation to the associated toxin(s). All tissues of A. retroflexus possessed an abundance of N-containing metabolites, particularly quaternary ammonium compounds which were identified as betaines, two of which (valine betaine and isoleucine betaine) are rarely encountered in plants. Cytotoxicity to murine fibroblasts was highest in extracts of leaf tissue and was associated with a single, a small modified peptide with high similarity to N-acetyl-L-α-aspartyl-L-alanyl-L-α-aspartyl-L-α-glutamyl-O-(carboxymethyl)-L-tyrosyl-L-leucinamide, a synthetic phosphotyrosyl mimic involved in cell signaling processes. One possible mode of action leading to acute renal failure in grazing livestock by a modified peptide such as this is proposed.

Summary Increasingly, weeds have been taking on global distributions. With the proliferation of invasive weeds has come the challenge of managing these species over broad geographical regions, with diverse habitats and political jurisdictions. Here, we review the management of Mikania micrantha Kunth (Asteraceae; mile-a-minute) throughout its invaded range, extending through most of the Pacific islands and southern and south-east Asia. Context matters when determining the best course of action for managing M. micrantha, as it has invaded a large variety of agricultural and natural systems. In Queensland, Australia and Florida, USA, M. micrantha has been targeted in relatively successful eradication campaigns, highlighting the importance of early detection and rapid response methods, while elsewhere in its invaded range, populations are either still increasing or showing limited signs of decline. An inter-regional approach to research and management should incorporate successful management strategies employed throughout the invaded range including, but not limited to, chemical and cultural control practices, manual and mechanical control, classical biological control using the rust fungus Puccinia spegazzinii, plant–plant competition and integrated approaches utilising two or more control methods concurrently. Additional knowledge of M. micrantha genetics is required to determine if management approaches could be fine-tuned for particular populations. Countries bordering the Mekong River formed a network in 2011 to co-ordinate the management of invasive species such as M. micrantha. Expanding such a collaborative approach to other regions could further reduce populations of M. micrantha and limit its spread.

The potential of multi-purpose barley (Hordeum vulgare L.) cultivars to suppress weeds while maintaining optimal yield and grain quality has been reported but not recently evaluated in replicated field trials performed under southern Australian field conditions. Therefore, to investigate this potential, aboveground competitive traits were assessed in nine genetically diverse commercial barley cultivars in 2015, 2016 and 2017, in two locations in the Riverina region of NSW in replicated field trials performed in the absence of pre-emergent herbicide treatment. Crop and weed establishment, early vigour, leaf area index, photosynthetically active radiation (PAR) and biomass were assessed at various crop growth stages, including early growth, vegetative, flowering, grain fill and harvest. Cultivar differences in crop and weed biomass accumulation at ~50, 100 and 150 days after planting were noted at both locations. Early barley biomass accumulation was inversely related to weed biomass in both locations and most years, suggesting strong (over 90%) potential for heritable competitive barley interference against weeds. The current study also observed a positive relationship between PAR light interception and crop biomass in all three years at both locations, suggesting that PAR light interception contributed positively to crop biomass accumulation by directly increasing photosynthesis (50–70%) and growth or indirectly influencing weed biomass accumulation (10–15%) and weed interference (50–75). Partial least squares modelling was performed with 2015 and 2016 datasets to assess the interactions between crop developmental traits and weed suppression. Cultivars exhibiting enhanced early vigour and PAR light interception were generally more weed suppressive under optimal higher soil moisture conditions. Our results indicate that the choice of barley cultivar has a significant impact on weed establishment, fecundity and seedbank dynamics. The use of competitive barley genotypes is, thus, a cost-effective strategy to reduce weed seedbank numbers over time and may reduce potential herbicide use.

Background: Silicon (Si) is known to have numerous beneficial effects on plants, alleviating diverse forms of abiotic and biotic stress. Research on this topic has accelerated in recent years and revealed multiple effects of Si in a range of plant species. Available information regarding the impact of Si on plant defence, growth and development is fragmented, discipline-specific, and usually focused on downstream, distal phenomena rather than underlying effects. Accordingly, there is a growing need for studies that address fundamental metabolic and regulatory processes, thereby allowing greater unification and focus of current research across disciplines. Scope and Conclusions: Silicon is often regarded as a plant nutritional ‘non-entity’. A suite of factors associated with Si have been recently identified, relating to plant chemistry, physiology, gene regulation and interactions with other organisms. Research to date has typically focused on the impact of Si application upon plant stress responses. However, the fundamental, underlying mechanisms that account for the manifold effects of Si in plant biology remain undefined. Here, the known effects of Si in higher plants relating to alleviation of both abiotic and biotic stress are briefly reviewed and the potential importance of Si in plant primary metabolism is discussed, highlighting the need for a unifying research framework targeting common underlying mechanisms. The traditional approach of discipline-specific work on single stressors in individual plant species is currently inadequate. Thus, a holistic and comparative approach is proposed to assess the mode of action of Si between plant trait types (e.g. C3, C4 and CAM; Si accumulators and non-accumulators) and between biotic and abiotic stressors (pathogens, herbivores, drought, salt), considering potential pathways (i.e. primary metabolic processes) highlighted by recent empirical evidence. Utilizing genomic, transcriptomic, proteomic and metabolomic approaches in such comparative studies will pave the way for unification of the field and a deeper understanding of the role of Si in plants.

l-Canavanine (CAN) is a non-protein amino acid (NPAA) possessing toxic properties in both animal and plant systems. Upon treatment, this arginine structural analogue is typically incorporated into proteins by arginyl-tRNA synthetase, leading to rapid functional disruption of such “canavanyl proteins”. CAN is produced in many legumes including jack bean and lucerne (alfalfa) and is accumulated mainly in seeds and their newly germinating sprouts. It has been described as a potent allelochemical and its toxicity has been associated with autoimmunological diseases in humans or animals feeding on plants containing this NPAA. Application of CAN even at low concentration resulted in an inhibition of plant growth. When CAN was used as an anticancer agent, its mode of action appears to be associated with the synthesis of non-functional proteins in sensitive organisms, a similar mode of action to that of other simple NPAAs as meta-tyrosine. CAN toxicity in plants is also likely associated with the formation of non-functional proteins and its application has been shown to cause disruption of polyamine metabolism and formation of reactive nitrogen species including nitric oxide (NO). In higher plants, CAN has recently been used as a tool to study the regulation or modulation of polyamine–NO cross-talk. Comparing to other related NPAAs that impact cellular function in living plant and animal systems CAN seems to have the highest toxic properties. The aim of this review is to describe CAN specific activity and mode of action especially focused on higher plant systems.

Isohexenylnaphthazarins are commonly found in the root periderm of several Boraginaceous plants and are known for their broad range of biological activities. The work described herein concerns the biological activity of compounds from the roots of Echium plantagineum L. and Echium gaditanum Boiss (Boraginaceae) collected from field sites in southern Spain and Australia. Bioactivity was assessed using etiolated wheat coleoptile bioassay and in vitro growth inhibitory activity in HeLa and IGROV-1 cells. The quantification of four isohexenylnaphthazarins (shikonin/alkannin, deoxyshikonin/deoxyalkannin, acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin) was performed by LC-MS/MS using juglone as internal standard. Correlation coefficient values for the activities and concentrations of these four analytes were in the linear range and were greater than 0.99. Acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin were present in the highest concentrations in extracts of both species. The results reveal that greatest overall inhibition was observed in both bioassays with E. gaditanum extracts. Strong correlations between time of collection, sampling location and bioactivity were identified.

Highlight Napthoquinones, antimicrobial and phytotoxic metabolites that are involved in plant defence, are produced and released into the rhizosphere by root hairs and root periderm tissue of Echium plantagineum., Bioactive plant secondary products are frequently the drivers of complex rhizosphere interactions, including those with other plants, herbivores and microbiota. These chemically diverse molecules typically accumulate in a highly regulated manner in specialized plant tissues and organelles. We studied the production and localization of bioactive naphthoquinones (NQs) in the roots of Echium plantagineum, an invasive endemic weed in Australia. Roots of E. plantagineum produced red-coloured NQs in the periderm of primary and secondary roots, while seedling root hairs exuded NQs in copious quantities. Confocal imaging and microspectrofluorimetry confirmed that bioactive NQs were deposited in the outer layer of periderm cells in mature roots, resulting in red colouration. Intracellular examination revealed that periderm cells contained numerous small red vesicles for storage and intracellular transport of shikonins, followed by subsequent extracellular deposition. Periderm and root hair extracts of field- and phytotron-grown plants were analysed by UHPLC/Q-ToF MS (ultra high pressure liquid chromatography coupled to quadrupole time of flight mass spectrometry) and contained more than nine individual NQs, with dimethylacrylshikonin, and phytotoxic shikonin, deoxyshikonin and acetylshikonin predominating. In seedlings, shikonins were first found 48h following germination in the root-hypocotyl junction, as well as in root hair exudates. In contrast, the root cortices of both seedling and mature root tissues were devoid of NQs. SPRE (solid phase root zone extraction) microprobes strategically placed in soil surrounding living E. plantagineum plants successfully extracted significant levels of bioactive shikonins from living roots, rhizosphere and bulk soil surrounding roots. These findings suggest important roles for accumulation of shikonins in the root periderm and subsequent rhizodeposition in plant defence, interference, and invasion success.

Conyza bonariensis (L.) Cronq. (syn. of Erigeron bonariensis L.) is a difficult-to-control summer weed species in the cropping belt of south-eastern Australia. Herbicide resistance may be affecting the ability to control C. bonariensis in the agricultural region of north-eastern Victoria; therefore, a survey was conducted to evaluate resistance to herbicides from several mode-of-action groups. Of the populations collected, 40% were resistant to glyphosate at 1080 g ha–1. Chlorsulfuron failed to control any of the populations collected. Further research identified multiple herbicide resistance to glyphosate, chlorsulfuron, metsulfuron-methyl and sulfometuron-methyl in five of nine populations fully characterised. Resistance was not found to 2,4-D, clopyralid or paraquat. There was no correlation between prevailing land use and the frequency of glyphosate-resistant populations, suggesting that resistance had been selected in multiple production systems. The high frequency of resistance could explain the difficulty experienced in controlling C. bonariensis across north-eastern Victoria and demonstrates the importance of integrated weed management to manage this weed.

Paterson’s curse (Echium plantagineum L. (Boraginaceae)), is an herbaceous annual native to Western Europe and northwest Africa. It has been recorded in Australia since the 1800’s and is now a major weed in pastures and rangelands, but its introduction history is poorly understood. An understanding of its invasion pathway and subsequent genetic structure is critical to the successful introduction of biological control agents and for provision of informed decisions for plant biosecurity efforts. We sampled E. plantagineum in its native (Iberian Peninsula), non-native (UK) and invaded ranges (Australia and South Africa) and analysed three chloroplast gene regions. Considerable genetic diversity was found among E. plantagineum in Australia, suggesting a complex introduction history. Fourteen haplotypes were identified globally, 10 of which were co-present in Australia and South Africa, indicating South Africa as an important source population, likely through contamination of traded goods or livestock. Haplotype 4 was most abundant in Australia (43%), and in historical and contemporary UK populations (80%), but scarce elsewhere (< 17%), suggesting that ornamental and/or other introductions from genetically impoverished UK sources were also important. Collectively, genetic evidence and historical records indicate E. plantagineum in southern Australia exists as an admixture that is likely derived from introduced source populations in both the UK and South Africa. Australian Research Council | Ref. DP130104346

Mixed farming systems have traditionally incorporated subterranean clover (Trifolium subterraneum L.) and lucerne (Medicago sativa L.) as key components of the pasture phase across south-eastern Australia. However, poor adaptation of subterranean clover to acidic soils, insufficient and inconsistent rainfall, high input costs, soil acidification and the emergence of herbicide-resistant weeds have reduced efficacy of some traditional clover species in recent years. To overcome these challenges, numerous novel pasture species have been selectively improved and released for establishment in Australia. Despite their suitability to Australian climate and soils, limited knowledge exists regarding their weed-suppressive ability in relation to establishment and regeneration. Field trials were therefore conducted over 3 years in New South Wales to evaluate the suppressive potential of selected pasture legume species and cultivars as monocultures and in mixed stands against dominant annual pasture weeds. Pasture and weed biomass varied significantly between pasture species when sown as monocultures, but mixtures of several species did not differ with regard to establishment and subsequent weed infestation. Arrowleaf clover (T. vesiculosum Savi.) and biserrula (Biserrula pelecinus L.) cv. Casbah showed improved stand establishment, with higher biomass and reduced weed infestation compared with other pasture species. Generally, weed suppression was positively correlated with pasture biomass; however, yellow serradella (Ornithopus compressus L.) cv. Santorini exhibited greater weed suppression than other pasture legumes while producing lower biomass, thereby suggesting a mechanism other than competition for resources affecting weed-suppressive ability. Over the period 2015–17, arrowleaf clover and biserrula cv. Casbah were generally the most consistent annual pasture legumes with respect to yearly regeneration and suppression of annual pasture weed species.

Barley grass (Hordeum spp.) is a relatively short lived annual that provides high quality grazing early in the season, but its seed heads cause contamination of wool and carcasses, and may irritate the mouth, eyes and nose of sheep. Treatments were imposed on established subterranean clover (Trifolium subterraneum L.) annual pasture in the same plots for three consecutive years (2015 to 2017) to evaluate changes in barley grass content. Treatments included: grazing alone (G), herbicide followed by grazing (HG), or a forage conservation harvest in early October, late October or early November consistent with an early silage harvest (ES), late silage harvest (LS) or hay cut (H). Grazing plus herbicide markedly reduced (P < 0.05) barley grass numbers compared with all other treatments, but increased (P < 0.05) the growth of annual ryegrass (Lolium rigidum L.). ES reduced (P < 0.05) barley grass and increased (P < 0.05) subterranean clover compared with H, but broadleaf weed content benefitted by LS in contrast to either ES or H. Although herbicide application was the most effective method for barley grass control, forage harvest timing could be used to beneficially manipulate pasture composition.

Geographically distinct populations of Paterson’s curse (Echium plantagineum L., Boragineacea), found near roadsides across New South Wales and Victoria, Australia were surveyed along 3 distinct longitudinal transects in spring of 2011 for presence of pyrrolizidine alkaloids and naphthoquinones in sampled plants. Composite samples of shoots and roots were collected from each of 45 sites; shoot extracts were subjected to solid phase extraction and LC-ESI/MS for determination of pyrrolizidine alkaloids (PAs) and related N-oxides (PANOs), while root periderm extracts were analysed for naphthoquinone content spectrophotometrically and by LC-ESI/MS. Metabolic profiling of 12 possible PAs and PANOs showed their consistent appearance in all shoot extracts, with lepthamine N-oxide, echimidine-N oxide and echumine N-oxide predominant. The three major PANOs were significantly higher in northern sampling locations than those further south. Root extracts contained shikonin and several related naphthoquinones, as well as two of the major PANOs found in the leaves. Naphthoquinones were highest in the northwest corner of the sampled region. The patterns of abundance of secondary metabolites in E. plantagienum suggest that climate change might result in greater production of defensive compounds by E. plantagineum, making this weed increasingly toxic to livestock.

Allelochemicals and other metabolites released by plant roots play important roles in rhizosphere signalling, plant defence and responses to abiotic stresses. Plants use a variety of sequestration and transport mechanisms to move and export bioactive products safely into the rhizosphere. The use of mutants and molecular tools to study gene expression has revealed new information regarding the diverse group of transport proteins and conjugation processes employed by higher plants. Transport systems used for moving secondary products into and out of root cells are similar to those used elsewhere in the plant but are closely linked to soil environmental conditions and local root health. Root cells can rapidly generate and release large quantities of allelochemicals in response to stress or local rhizosphere conditions, so the production and transport of these compounds in cells are often closely linked. Plants need to manage the potentially toxic allelochemicals and metabolites they produce by sequestering them to the vacuole or other membrane-bound vesicles. These compartments provide secure storage areas and systems for safely moving bioactive chemicals throughout the cytosol. Release into the apoplast occurs either by exocytosis or through membrane-bound transport proteins. This review discusses the possible transport mechanisms involved in releasing specific root-produced allelochemicals by combining microscopic observations of the specialized root cells with the physical and chemical properties of the exudates.

The introduced exotic vines pale and black swallowwort rapidly have become invasive throughout regions of the northeastern United States and adjoining areas of Canada. Preliminary studies have reported that the species are allelopathic, possibly contributing to their competitive ability and invasiveness. Results from our laboratory assays indicated that swallowwort root exudates caused significant root length reductions (e.g., 40% for butterfly milkweed and 20% for large crabgrass) and reduced germination (e.g., 25% for lettuce) of indicator species. Additional bioassays with dried swallowwort tissues demonstrated that tissue leachates caused varied responses in indicators, with both significant stimulatory and inhibitory effects. In particular, significant congeneric interactions were noted between the two swallowwort species. Evidence from this study of swallowwort tissue phytotoxicity has important implications for developing effective management and habitat restoration strategies for the two invasive species.

Jerusalem artichoke has been reported to colonize several ecological niches and agronomic crops in southern Europe. This plant is also of interest because of its high biomass production and its potential to produce ethanol for biofuel. Allelopathy may be an advantageous trait in Jerusalem artichoke under cultivation, as it potentially reduces weed interference with the crop, theoretically allowing a reduction of mechanical or chemical input required for weed management. However, this trait may also be unfavorable if other crops are cultivated in rotation with Jerusalem artichoke or in areas infested by this species. The aim of this study was to investigate the sensitivity of selected diverse crops (wheat, lettuce, corn, tomato, rice, and zucchini) and weeds (barnyardgrass, black nightshade, common lambsquarters, common purslane, large crabgrass, and pigweed) to the presence of Jerusalem artichoke dried leaf tissues in laboratory experiments performed under controlled conditions. The simulated soil incorporation of different Jerusalem artichoke residues (four cultivars and a weedy population) was carried out in a series of laboratory and greenhouse experiments. Jerusalem artichoke reduced the radicle growth of seedling lettuce (60%), tomato (30%), large crabgrass (70%), and barnyardgrass (30%), whereas total germination of these species was less affected. Sensitivity to Jerusalem artichoke residues was species dependent; germination and initial growth of corn were not affected, whereas winter wheat, lettuce, tomato, rice, and zucchini seedlings were more sensitive to residue presence. Our experiments show that both wild and cultivated decomposing Jerusalem artichoke residues, particularly leaves and stems, possess phytotoxic potential. Additional field experimentation remains to be conducted to determine if allelopathy in the field contributes to its invasibility.

Annual ryegrass (Lolium rigidum Gaud.) is a troublesome invasive plant in southern Australian cropping systems and is typically infected with a fungal endophyte, Epichloë occultans. Potential links between herbicide resistance and endophyte infection were investigated in this study. We surveyed 391 ryegrass populations from geographically distinct, naturalised pasture and cropping areas across southern Australia and compared frequencies of seed-borne endophyte infection in the collected seed samples from mature annual ryegrass. Data on herbicide resistance from similar seedlots were cross-referenced with endophyte infection frequency to examine the potential relationship between herbicide resistance and endophyte infection. Seeds from cropping paddocks exhibited a significantly higher frequency of endophyte infection than pasture paddocks sampled from the same region. Frequencies of endophyte infection in annual ryegrass declined across Australia during 2001–09, whereas the opposite trend was observed during 2009–12. Impacts of the Australian Millennium Drought, the correspondingly altered rainfall patterns and environmental selection pressures have a role in determining observed endophyte infection frequencies. However, there was no significant correlation between endophyte frequency and herbicide resistance in the populations evaluated. Differences in endophyte infection frequencies were associated with farming practices, and require further examination to determine causative selection pressures encountered in Australian field settings.

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.

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.

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 ...

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...

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.

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.'

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 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.

Sorghum [Sorghum bicolor (L.) Moench] roots exude a potent bioherbicide known as sorgoleone, which is produced in living root hairs and is phytotoxic to broadleaf and grass weeds at concentrations as low as 10 microM. Differential gene expression was studied in sorghum (S. bicolorxS. sudanense) cv. SX17 between roots with abundant root hairs and those without root hairs using a modified differential display approach. A differentially expressed gene, named SOR1, was cloned by using Rapid Amplification of the 5' ends of cDNA (5'-RACE). Real-time PCR analysis of multiple tissues of sorghum SX17 revealed that the SOR1 transcript level in root hairs was more than 1000 times higher than that of other tissues evaluated, including immature leaf, mature leaf, mature stem, panicle, and roots with hairs removed. Semi-quantitative RT-PCR revealed that SOR1 was expressed in the sorgoleone-producing roots of sorghum SX17, shattercane [S. bicolor (L.) Moench], and johnsongrass [S. halepense (L.) Pers.], but not in the shoots of sorghum or in the roots of sweet corn (Zea mays L.) 'Summer Flavor 64Y', in which sorgoleone production was not detected by HPLC analysis. Similarity searches indicated that SOR1 probably encodes a novel desaturase, which might be involved in the formation of a unique and specific double bonding pattern within the long hydrocarbon tail of sorgoleone.

Rhizo-lysimeters offer unique advantages for the study of plants and their interactions with soils. In this paper, an existing facility at Charles Sturt University in Wagga Wagga Australia is described in detail and its potential to conduct both ecophysiological and ecohydrological research in the study of root interactions of agricultural crops and pastures is quantitatively assessed. This is of significance to future crop research efforts in southern Australia, in light of recent significant long-term drought events, as well as potential impacts of climate change as predicted for the region. The rhizo-lysimeter root research facility has recently been expanded to accommodate larger research projects over multiple years and cropping rotations.Lucerne, a widely-grown perennial pasture in southern Australia, developed an expansive root system to a depth of 0.9 m over a twelve month period. Its deeper roots particularly at 2.05 m continued to expand for the duration of the experiment. In succeeding experiments, canola, a commonly grown annual crop, developed a more extensive (approximately 300%) root system than wheat, but exhibited a slower rate of root elongation at rates of 7.47 x 10-3 m day-1 for canola and 1.04 x10-2 m day-1 for wheat. A time domain reflectometry (TDR) network was designed to accurately assess changes in soil water content, and could assess water content change to within 5% of the amount of water applied.The rhizo-lysimetry system provided robust estimates of root growth and soil water change under conditions representative of a field setting. This is currently one of a very limited number of global research facilities able to perform experimentation under field conditions and is the largest root research experimental laboratory in the southern hemisphere.

Primer design is a critical step in the application of PCR-based technologies in gene expression and genetic diversity analysis. As more plant genomes have been sequenced in recent years, the emphasis of primer design strategy has shifted to genome-wide and high-throughput direction. This paper summarizes recent advances in primer design for profiling of DNA polymorphism and mRNA in higher plants, as well as new primer systems developed for animals that can be adapted for plants.

Aqueous extracts of quackgrass [Agropyron repens(L.) Beauv. # AGRRE] shoots and rhizomes inhibited seed germination and root growth of alfalfa (Medicago sativaL. ‘Vernal’), soybean (Glycine max(L.) Merr. ‘Corsoy 79’], navybean (Phaseolus vulgarisL. ‘Seafarer’), and curly cress (Lepidium sativumL.) at concentrations of less than 2.5 mg dried extract/ml. Extracts of quackgrass shoots were generally more inhibitory than extracts of rhizomes. Root and shoot dry weights of snapbeans (Phaseolus vulgarisL. ‘Bush Blue Lake’) grown under sterile conditions were reduced by aqueous extracts of shoots. Root systems were stunted and necrotic and lacked root hairs. The growth ofRhizobiumspecies was not influenced by the presence of 40 or 80 mg/ml concentrations of extracts of shoots or rhizomes. Quackgrass may inhibit indirectly the legume-Rhizobiumsymbiosis by inhibiting root hair formation rather than directly inhibitingRhizobiumgrowth. The presence of soil microorganisms was not necessary for the development of quackgrass toxicity in soil or agar. Soil microorganisms reduced toxicity of quackgrass residues in soil.

Pronounced differences in the tolerance of tomatoes and bell peppers to clomazone observed in field studies were confirmed in a greenhouse experiment. In greenhouse studies, preemergence clomazone rates causing 50% visible injury on bell pepper and tomato seedlings 10 days after application were 9.4 and 0.1 kg/ha, respectively. Based on growth inhibition, bell peppers were 40-fold more tolerant of clomazone than tomatoes 20 days after clomazone application. In laboratory studies investigating the basis for differential clomazone tolerance, no differences in uptake of 14C-clomazone from nutrient solutions between tomato and bell pepper plants were observed after 24 h. Minor differences were observed in the distribution of 14C label within plants; a higher percentage of 14C was recovered in bell pepper roots than in tomato roots, while the opposite was true for the shoots. Clomazone was metabolized to two products in roots of both bell peppers and tomatoes within 48 h after treatment. Tomato shoots were more active in converting clomazone to these metabolites than were tomato roots. Bell pepper roots converted more clomazone to metabolites than did tomato roots 24 h after treatment. However, by 72 h, differences in clomazone metabolite levels between species were negligible in both roots and shoots. Enzymatic and acid hydrolysis of soluble, polaf clomazone metabolites indicated that these metabolites may be sugar conjugates of clomazone.

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