Challenges, achievements and opportunities in allelopathy research

Abstract

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 interference mechanisms?, and (vi) how can new achievements in allelopathy research aid in solving problems related to relevant ecological issues encountered in research conducted upon natural systems and agroecosystems? A greater knowledge of plant interactions in ecologically relevant environments, as well as the study of biochemical pathways, will enhance our understanding of the role of allelopathy in agricultural and natural settings. In addition, novel findings related to the relevant enzymes and genes involved in production of putative allelochemicals, allelochemical persistence in the rhizosphere, the molecular target sites of allelochemicals in sensitive plant species and the influence of allelochemicals upon other organisms will likely lead to enhanced utilization of natural products for pest management or as pharmaceuticals and nutraceuticals. This review will address these recent findings, as well as the major challenges which continue to influence the outcomes of allelopathy research.

Interactions between allelochemicals and the microbial community affect weed suppression following cover crop residue incorporation into soil

“…2). The rapid onset of a strongly antagonistic microbe-by-extract effect indicates that a focus on easily extractable chemical components of cover crop residues may overestimate their potential for weed suppression in natural settings with soil microorganisms present, and our results underscore the message of previous researchers that soil microorganisms are understudied but critically important mediators of important exterminators of allelopathic activity (Inderjit 2005;Inderjit et al 2005). This antagonistic microbe-by-extract interaction may indicate microbial degradation of phytotoxic compounds.…”

“…We suggest that the allelochemicals in fresh residues were more protected from microbial degradation than when they were added as extracts, giving fresh red clover residues a longer lasting suppressiveness. While we used only the aerial parts of the red clover plant for our experiment, the roots of the plant would also be present in green manured systems; because these roots can also be a source of allelochemicals (Forney and Foy 1985;Inderjit et al 2005), they may provide additional weed suppression that what we can document here. We identified formononetin as the most important allelochemical in the fresh residue treatments (Fig.…”

“…These insoluble allelochemicals can constitute a significant fraction of total allelopathic potential of a cover crop residue (Harper and Lynch 1982), so microbes may slowly release residue-derived allelochemicals, extending the longevity of a cover crop's effectiveness. Given that agricultural soils are not sterile, it is important to understand how microbial activity moderates allelochemical potential of cover crop residues (Inderjit 2005;Inderjit et al 2005).…”

Phytotoxicity induced by Phragmites australis: an assessment of phenotypic and physiological parameters involved in germination process and growth of receptor plant

“…Generally, phytotoxic activity in nature depends on the release of a mixture of phytotoxins and joint effects of them rather than an individual chemical (Reigosa et al 1999;Inderjit & Duke 2003). Hence, plant extracts with phytotoxins showing synergistic, additive, or antagonistic mixture effects were shown to have higher and longer lasting effects on target species than individual chemical (Inderjit et al 2005;Koul & Walia 2009).…”

Bioassay-guided isolation of allelochemicals from Avena sativa L.: allelopathic potential of flavone C-glycosides

“…In natural environments, allelopathy has been implicated in plant invasions, which is a major ecological problem (Bousquet-Mélou et al 2005). In agriculture, the release of toxic substances into the soil can be exploited not only for sustainable cropping systems in crop rotation, but also for weed management systems through the use of cover crops (Putnam 1986;Weston 1996;Duke et al 2000a;Weston and Duke 2003;Inderjit et al 2005).…”