Novel and holistic approaches are required to realize allelopathic potential for weed management

Allelopathy, that is, plant–plant inhibition via the release of secondary metabolites into the environment, has potential for the management of weeds by circumventing herbicide resistance. However, mechanisms underpinning allelopathy are notoriously difficult to elucidate, hindering real-world application either in the form of commercial bioherbicides or allelopathic crops. Such limited application is exemplified by evidence of limited knowledge of the potential benefits of allelopathy among end users. Here, we examine potential applications of this phenomenon, paying attention to novel approaches and influential factors requiring greater consideration, with the intention of improving the reputation and uptake of allelopathy. Avenues to facilitate more effective allelochemical discovery are also considered, with a view to stimulating the identification of new compounds and allelopathic species. Synthesis and Applications: We conclude that tackling increasing weed pressure on agricultural productivity would benefit from greater integration of the phenomenon of allelopathy, which in turn would be greatly served by a multi-disciplinary and exhaustive approach, not just through more effective isolation of the interactions involved, but also through greater consideration of factors which may influence them in the field, facilitating optimization of their benefits for weed management

Review: Allelochemicals as multi-kingdom plant defence compounds: towards an integrated approach

© 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. The capability of synthetic pesticides to manage weeds, insect pests and pathogens in crops has diminished due to evolved resistance. Sustainable management is thus becoming more challenging. Novel solutions are needed and, given the ubiquity of biologically active secondary metabolites in nature, such compounds require further exploration as leads for novel crop protection chemistry. Despite improving understanding of allelochemicals, particularly in terms of their potential for use in weed control, their interactions with multiple biotic kingdoms have to date largely been examined in individual compounds and not as a recurrent phenomenon. Here, multi-kingdom effects in allelochemicals are introduced by defining effects on various organisms, before exploring current understanding of the inducibility and possible ecological roles of these compounds with regard to the evolutionary arms race and dose–response relationships. Allelochemicals with functional benefits in multiple aspects of plant defence are described. Gathering these isolated areas of science under the unified umbrella of multi-kingdom allelopathy encourages the development of naturally-derived chemistries conferring defence to multiple discrete biotic stresses simultaneously, maximizing benefits in weed, insect and pathogen control, while potentially circumventing resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry

STAGES IN THE ORIGIN OF VERTEBRATES: ANALYSIS BY MEANS OF SCENARIOS

Vertebrates lack an epidermal nerve plexus. This feature is common to many invertebrates from which vertebrates differ by an extensive set of shared-derived characters (synapomorphies) derived from the neural crest and epidermal neurogenic placodes. Hence, the hypothesis that the developmental precursor of the epidermal nerve plexus may be homologous to the neural crest and epidermal neurogenic placodes. This account attempts to generate a nested set of scenarios for the prevertebrate-vertebrate transition, associating a presumed sequence of behavioural and environmental changes with the observed phenotypic ones. Toward this end, it integrates morphological, developmental, functional (physiological/behavioural) and some ecological data, as many phenotypic shifts apparently involved associated transitions in several aspects of the animals. The scenarios deal with the origin of embryonic and adult tissues and such major organs as the notochord, the CNS, gills and kidneys and propose a sequence of associated changes. Alternative scenarios are stated as the evidence often remains insufficient for decision. The analysis points to gaps in comprehension of the biology of the animals and therefore suggests further research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72629/1/j.1469-185X.1989.tb00471.x.pd

Getting to the roots of black-grass: allelopathic interactions for control of Alopecurus myosuroides

Black-grass is a highly detrimental herbicide-resistant grass weed of arable agriculture in Europe. While cultural controls can partially mitigate black-grass, there remains great need for additional alternative control methods. A potential alternative approach to weed control is to harness the allelopathy (biochemical inhibition) of potent species. Cereals like wheat and rye synthesise and exude from their roots a class of compounds, benzoxazinoids, which have both plant-plant allelopathic potential, and other multi-kingdom inhibitory effects. Petri dish assays of benzoxazinoid compounds with documented allelopathic potential identified 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) as promising compounds in inhibiting root development in black-grass populations, with inhibition unrelated to variability in herbicide resistance profile. Wheat is highly tolerant of these compounds, indicating species-specificity in their allelopathic potential. Crude cereal root exudates collected in hydroponic and axenic sand systems were also examined for allelopathic potential. Therein, wheat and rye exudates were confirmed as inhibitory, while a wider range of inhibitory potential was found in exudates of ancestor wheats. Subsequent chemical analyses of these exudates tentatively identified a suite of benzoxazinoid compounds present, with those related to DIMBOA exuded from modern wheat, and those related to DIBOA exuded from rye and ancestor wheats. Selection for DIMBOA synthesis may thus be an unintended consequence of wheat domestication. 2-hydroxy-1,4-benzoxazin-3-one (HBOA) was noted as another potential allelochemical, which was examined and confirmed as a potent black-grass inhibitor. Crude cereal exudates were capable of allelopathy towards black-grass in soil, but benzoxazinoids degraded quickly in many soils, reducing their inhibitory potential. This explains the greater efficacy of biological crop treatments exuding allelochemicals towards black-grass, in comparison to synthetic chemical treatments when applied in combination in glasshouse assays. Further dose-response analyses of the more persistent DIBOA-related compound 4-hydroxy-1,4 benzoxazin-3-one(D-DIBOA) identified that it is not an effective black-grass inhibitor, indicating that another allelochemical must be identified for the development of a pure bioherbicide. Therefore, it is concluded that an allelopathic crop is a more realistic application of benzoxazinoid inhibitors for black-grass control, in combination with effective deployment of cultural control methods

A new molecular phylogeny-based taxonomy of parasitic barnacles (Crustacea: Cirripedia: Rhizocephala)

Rhizocephalans are abundant members of marine ecosystems and are important regulators of crustacean host populations. Morphological and ecological variation makes them an attractive system for evolutionary studies of advanced parasitism. Such studies have been impeded by a largely formalistic taxonomy, because rhizocephalan morphology offers no characters for a robust phylogenetic analysis. We use DNA sequence data to estimate a new phylogeny for 43 species and use this to develop a revised taxonomy for all Rhizocephala. Our taxonomy accepts 13 new or redefined monophyletic families. The traditional subdivision into the suborders Kentrogonida and Akentrogonida is abandoned, because both are polyphyletic. The three ‘classical’ kentrogonid families are also polyphyletic, including the species-rich Sacculinidae, which is split into a redefined and a new family. Most species of large families remain to be studied based on molecular evidence and are therefore still assigned to their current genus and family by default. We caution against undue generalizations from studies on model species until a more stable species-level taxonomy is also available, which requires more extensive genus- and species-level sampling with molecular tools. We briefly discuss the most promising future studies that will be facilitated by this new phylogeny-based taxonomy

No evidence for root-mediated allelopathy in Centaurea solstitialis, a species in a commonly allelopathic genus

Phytotoxicity bioassays and pot experiments using activated carbon both suggest that Centaurea solstitialis (yellow star-thistle) does not rely on phytotoxic root exudates for invasion of California grasslands. Pot experiments in which five native species were grown in the presence/absence of C. solstitialis and in the presence/absence of activated carbon (fully crossed design) showed that C. solstitialis competitively suppressed native species, but did not inhibit them through allelochemicals. In separate experiments examining the role of root exudates in invasion success, treatment with crude root exudates and chloroform-extracted root exudates from C. solstitialis reduced growth of the model plant Arabidopsis thaliana. However, high concentrations of the exudates (50%, v/v or 500 μg mL-1) were required to inhibit A. thaliana growth and did not result in A. thaliana mortality, suggesting the presence of only a weak growth inhibitor. Moreover, high concentrations of C. solstitialis crude root exudates did not affect the growth of five native grass species often displaced by C. solstitialis invasions in California grasslands. Finally, root exudates collected from C. solstitialis had weaker effects on a native California root parasite, Triphysaria versicolor, than root exudates collected from Zea mays, a species not renowned for its competitive or invasive capabilities. Our results suggest that, while C. solstitialis might possibly "be persuaded to yield a product that is toxic to one species or another" (Population biology of plants, Academic, 1977), we find no evidence that allelopathic root exudates play a role in the competitive success of this invasive.Fil: Qin, Bo. Colorado State University; Estados UnidosFil: Lau, Jennifer A.. University of California; Estados UnidosFil: Kopshever, Joseph. University of California; Estados UnidosFil: Callaway, Ragan M.. University of Montana; Estados UnidosFil: McGray, Heather. University of California; Estados UnidosFil: Perry, Laura G.. Colorado State University; Estados UnidosFil: Weir, Tiffany L.. Colorado State University; Estados UnidosFil: Paschke, Mark W.. Colorado State University; Estados UnidosFil: Hierro, Jose Luis. University of Montana; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Yoder, John. University of California; Estados UnidosFil: Vivanco, Jorge M.. Colorado State University; Estados UnidosFil: Strauss, Sharon. University of California; Estados Unido