Allelopathy: Current Status and Future Goals

Abstract

The phenomenon of allelopathy encompasses all types of chemical interactions among plants and microorganisms. Several hundred different organic compounds (allelochemicals) released from plants and microbes are known to affect the growth or aspects of function of the receiving species. Many new allelochemicals have been identified in recent years and it has become clear that the actions of allelochemicals are important features characterizing the interrelationships among organisms. These compounds influence patterns in vegetational communities, plant succession, seed preservation, germination of fungal spores, the nitrogen cycle, mutualistic associations, crop productivity, and plant defense. Allelopathy is tightly coupled with competition for resources and stress from disease, temperature extremes, moisture deficit, and herbicides. Such stresses often increase allelochemical production and accentuate their action. Allelopathic inhibition typically results from a combination of allelochemicals which interfere with several physiological processes in the receiving plant or microorganism. Other than the autecological study of specific species, there are persistent challenges in allelopathy to determine the mechanism of action of compounds, isolate new compounds, evaluate environmental interactions, and understand activity in the soil. New frontiers will focus on ways to capitalize on allelopathy to enhance crop production and develop a more sustainable agriculture, including weed and pest control through crop rotations, residue management, and a variety of approaches in biocontrol. Other goals are to adapt allelochemicals as herbicides, pesticides, and growth stimulants, modify crop genomes to manipulate allelochemical production, and better elucidate chemical communications that generate associations between microorganisms and higher plants. 0097 ALLELOPATHY: ORGANISMS, PROCESSES, AND APPLICATIONSThe writings of some natural philosophers that date back more than two millenniums show that they recognized chemical influences in nature (1). However, it is the evidence accumulated over the last several decades which has established that external roles for biochemicals, meaning roles that do not directly affect the basic physiology of the producing organism, are pervasive themes characterizing the interrelationships among organisms. This realization does not diminish the respective importance that competition for resources has on the relative success of an organism or a species. Instead, chemical ecology extends our dimensions of understanding and provides new insights into the intricacies of interchanges that occur in an ecosystem, community, or population.Allelopathy, a subset within the broader scope of chemical ecology, is concerned with effects that chemicals of plant or microbial origin have on growth, development, and distribution of other plants and microorganisms in natural communities or agricultural systems. The aims of this overview chapter are to provide a synthesis of the scope of allelopathy, suggest gen...

AUTOTOXICITY IN TOUGH LOVEGRASS ( Eragrostis plana )

“…In the case of autotoxicity, they are also called autochemicals or simply phytotoxins and can be released by leaves, roots, stems, fruits, seeds, cotyledons, rhizomes, inflorescences, leaf litter, and plant residues (Singh et al, 1999). The chemical nature of these compounds include simple organic acids, straight-chain alcohols, aldehydes or ketones, lactones unsaturated, fatty acids, naphthoquinones, quinone complex, simple phenols, tannins, terpenoids, amino acids, polypeptides, alkaloids, glucosinolates, purines and nucleotides (Einhellig, 1995;Rice, 1995).…”

Effect of benzoic acid hydroxyl- and methoxy-ring substituents on cucumber (Cucumis sativusL.) root membrane potential

“…Rapid Vm changes after perfusion of some BAs confirm the general hypothesis that BAs act at the plasma membrane level (Blake 1985, Heipieper et al 1991, Einhellig 1995, Baziramakenga et al 1995, Seigler 1996, Crisan et al 2007). The results obtained in this study give evidence for a differential effect of BA ring substituents on Vm, with a transient strong Vm depolarization, after perfusion by almost all BA methoxy-ring substituents.…”

“…Since Cs ' transport is not relevant to the overall ion movement (Bellando et al 1995) it seems reasonable to suppose that the above BAs might have an effect on the mechanism of Cs ' inhibitory action on K ' inward channels, even though the effects of Cs ' may also be indirect. Alternatively, these BAs might act on H ' pump operation, by affecting ATPase and/or ATP production, as suggested by some authors (Einhellig 1995, Yu & Matsui 1997. However, a preliminary result on H ' extrusion following pA incubation in cucumber root segments does not support the hypothesis of an increased H ' -ATPase activity (Camusso et al unpublished).…”

“…Many phenolic compounds possess allelopathic properties able to produce direct or indirect effects on the growth and development of plants of the same or other species (Siqueira et al 1991, Einhellig 1995, Blum 1996, Inderjit 1996, Seigler 1996, Maffei et al 1999, Klejdus & Kuban 1999, Reigosa et al 1999, Huang et al 2000, Inderjit et al 2002, Politycka 2002, Batish et al 2007). Previous studies have demonstrated that in Cucumis sativus some phenolic compounds cause growth inhibition and decrease crop yield , Gerig & Blum 1991, Shafer & Blum 1991, Yu & Matsui 1997, Politycka 2002, Yu et al 2003, Politycka & Bednarski 2004.…”

“…Several ways of action are involved in the allelochemical interaction with biochemical and metabolic processes and one of the specific effects of phenolic compounds is the modification of membrane permeability and function (Bergmark et al 1992, Booker et al 1992, Barkosky & Einhellig 1993, Lehman et al 1994, Einhellig 1995, Blum 1996, Seigler 1996, Yu & Matsui 1997, Sacco & Maffei 1997, Sene et al 2000, Barkosky & Einhellig 2003, Gniazdowska & Bogatek 2005, Pehlivan & Arslan 2006. Studies on the influence of phenolic compounds on ion uptake and alteration of transmembrane potential difference (Vm) indicate that some BA derivatives are able to cause a rapid membrane depolarization, owing to their effects on either the diffusion potential or the electrogenic potential of plant root cells (Blake 1985).…”