The term allelopathy refers to the deleterious effect that a higher plant has on another through the production of chemical retardant that escape into the environment. Molisch (1937) coined the term as biochemical interactions between all types of plant including microorganisms. The term cover both detrimental and beneficial reciprocal biochemical interactions (Rice 1974). However, the term allelopathy is derived from two Greek words “allelos” (mutual) and “pathos” (suffering) meaning mutual harm expressing one plant releases inhibitory substances which inhibits the growth of other plant sharing the same habitat (Rice 1974; Chou 2006; Kostina-Bednarz et al., 2023). Allelopathy was defined as ‘any direct or indirect harmful effect by one plant on another (including micro-organisms) through production of chemical compounds that escape into the environment’ (Rice 1974). Allelopathy is an ecological phenomenon impacting ecosystem dynamics. The allelopathic interaction studies have been reported in ecological relationships between plants and microorganisms and between species of each group (Gomes et al., 2017).
Plants with allelopathic potential against other organisms induce changes in ecosystem properties (Wardle et al., 2007). Soil microorganisms are mediator of plant allelopathy and are recognized as an essential predictor of the outcome of allelopathic interactions between plants (Zeng 2014). Allelochemicals are present in all kinds of plants and tissues and are released in rhizosphere soil by decomposition of residues, as volatiles, leaf leachates and root exudation (Weston and Duke 2003; Thiebaut et al., 2019). Allelochemicals and signaling chemicals released in the environment regulate the interactions between plant and other organisms. Allelochemical is a plant defense response to suppress plant competitor and defend themselves against pathogens and herbivores. Signaling chemicals detect competitors, herbivores and pathogens and induce production and release of plant defensive metabolites (Kong et al., 2019).
Allelochemicals are non-nutritive substances mainly produced as plant secondary metabolites or decomposition products of microbes are active media of allelopathy (Cheng and Cheng 2015). Recent studies suggest that allelopathic properties render one species more invasive to native species and thus is detrimental to agricultural and naturalized settings (Weston and Duke 2003). The most volatile chemicals such as terpenoids are emitted by crop plants in drought-stricken areas whereas, the plant in humid zones release phytotoxins that are hydrophilic in nature including phenolics, flavonoids and alkaloids (Rahaman et al., 2022). The allelochemical released by the crop plant not only suppress weeds but also promote underground microbial activities (Jabran et al., 2015). Allelochemicals my cause oxidative stress in tissues and induce antioxidant mechanisms. The monoterpenoid emitted from many aromatic plants including forest trees is a-pinene. (Singh et al., 2006). Membrane disruption by monoterpenoids, is a mechanism for their fungicidal and bactericidal activity resulting in cell death. Enhanced lipid peroxidation and electrolyte leakage results in loss of membrane integrity (Singh et al., 2006). The fescue (Festuca sp.) grasses displace neighboring plants by depositing aqueous phytotoxic root exudate in the rhizosphere (Bertin et al., 2007).
Different microbial species are associated with different plant species due to species specific rhizosphere biochemistry as well as due to difference in amount and quality of root exudate. The weak effect of root exudates of invasive species on old neighbors and the strong effect of the same exudates on new and native neighbors suggest plant can evolve tolerance to the unique rhizosphere biochemistry of co-occurring species (Callaway and Ridenour 2004). Allelochemical released by plants is factor in the competition of habitat expansion. The Stellera chamaejasme L., a perennial herb release allelochemicals which may be a mechanism for its invasion affecting the soil microbial community (Cheng et al., 2022). Root-associated fungi can affect plant allelopathy by degrading or transforming allelochemicals (Liu et al., 2018). Secalonic acid F (SAF) was an allelochemical produced by Aspergillus japonicus. SAF may weaken the protective ability of plant tissues against membrane lipid peroxidation and damage the whole membrane system of plants, resulting in ultrastructure damage of chloroplast, mitochondria and nuclei (Zeng et al., 2001). An allelochemical 8-hydroxyquinoline was identified in the root extract of Centaurea diffusa an invasive (Vivanco et al., 2004). Allelochemical display strong antibacterial and antifungal activity against pathogens such as Aspergillus niger, Rhizoctonia solani, Phytophthora infestans, Fusarium oxysporum, Xanthomonas compestris etc. (Li et al., 2010). C. diffusa is benefitted by 8-hydroxyquinoline as it has both phytotoxic and antimicrobial effect (Vivanco et al., 2004).
Solidago canadensis L. is an invasive and strong allelopathic plant species suppresses soil-borne pathogens through exudation of allelochemicals (Zhang et al., 2009). Allelopathic compound released by invasive plant can suppress growth of plant in their vicinity. The root of radish treated with aqueous extracts of knotweeds (Fallopia japonica and F. xbohemica)rhizomes showed suppressed growth. Furthermore, sign of cell damage and oxidative stress in the root cap cells, as well as abnormal shape of nuclei, mitochondria, endoplasmic reticulum and plasma membrane detached from the cell wall were the prominent effects in the root cap cells (Soln et al., 2022). Soil microorganisms interact with plant in a diversified manner. Allelopathy shapes plant communities and alters soil microbial diversity.
References:
Bertin, C., Weston, L. A., Huang, T. and Schroeder, F. C. 2007 Grass Roots Chemistry: Meta-Tyrosine, an Herbicidal Non-protein Amino Acid. PNAS 104(43): 16964 -16969
doi.org/10.1073/pnas.0707198104
Callaway, R. M. and Ridenour, W. M. 2004 Novel Weapons: Invasive Success and the Evolution of Increased Competitive Ability. Front. Ecol. Env. 2(8): 436 – 443
doi.org/10.1890/1540-9295(2004)002[0436:NWISATj2.0.CO;2
Cheng, F. and Cheng, Z. 2015 Research Progress on the Use of Plant Allelopathy in Agriculture and the Physiological and Ecological Mechanisms of Allelopathy. Front. Plant Sci. 6: 1020
doi: 10.3389/fpls.2015.01020
Cheng, J., Jin, H., Zhang, J., Xu, Z., Yang, X., Liu, H., Xu, X., Min, D., Lu, D. and Qin, B. 2022 Effects of Allelochemicals Soil Enzymes Activities and Environmental Factors on Rhizosphere Soil Microbial Community of Stellera chamaejasme L. along a Growth-Coverage Gradient. Microorganisms 10(1): 158
doi: 10.3390/microorganisms10010158
Chou, C-H. 2006 Introduction to Allelopathy. In: “Allelopathy”. Pages 1- 9
doi: 10.1007/1-4020-4280-9_1
Gomes, M. P., Garcia, Q. S., Barreto, L. C., Pimenta, L. P. S., Matheus, M. T. and Figueredo, C. C. 2017 Allelopathy: An Overview from Micro- to Macroscopic Organisms, from Cells to Environments and the Perspectives in a Climate-Changing World. Biologia 72(2): 113 – 129
doi: 10.1515/biolog-2017-0019
Jabran, K., Mahajan, G., Sardana, V. and Chauhan, B. S. 2015 Allelopathy for Weed Control in Agricultural Systems. Crop Protection 72: 57 – 65
doi.org/10.1016/j.cropro.2015.03.004
Kong, C-H., Xuan, T. D., Khanh, T. D., Tran, H-D. and Trung, N. T. 2019 Allelochemicals and Signaling Chemicals in Plants. Molecules 24(15): 2737
doi: 10.3390/molecules24152737
Kostina-Bednarz, M., Plonka, J. and Barchanska, H. 2023 Allelopathy as a Bioherbicides: Challenges and Prospects for Sustainable Agriculture. Reviews in Environmental Science and Bio/Technology 22: 471 – 504
doi.org/10.1007/s11157-023-09656-1
Li, Z-H., Wang, Q., Ruan, X., Pan, C-D. and Jiang, D-A. 2010 Phenolics and Plant Allelopathy. Molecules 15(12): 8933 – 8952
doi: 10.3390/molecules15128933
Liu, S., Qin, F. and Yu, S. 2018 Eucalyptus urophylla Root-associated Fungi can Counteract the Negative Influence of Phenolic Acid Allelochemicals. Appl. Soil Ecol. 127: 1 – 7
doi.org/10.1016/j.apsoil.2018.02.028
Rahaman, F., Juraimi, A. S., Rafii, M. Y., Uddin, K., Hassan, L., Chowdhury, A. K., Karim, S. M. R., Rini, B. Y., Yusuff, O., Basher, H. M. K. and Hossain, A. 2022 Allelopathic Potential in Rice-A Biochemical Tool for Plant Defence against Weeds. Front. Plant Sci. 13: 1072723
doi: 10.3389/fpls.2022.1072723
Rice, E. L. 1974 Introduction- meaning and origin of the term allelopathy. In: “Allelopathy”. Academic Press Inc. New York. Chapter 1 Pages 1-2
http://ndl.ethernet.edu.et/bitstream/123456789/43449/1/Elroy%20L.%20Rice.pdf
Singh, H. P., Batish, D. R., Kaur, S., Arora, K. and Kohli, R. K. 2006 a-Pinene Inhibits Growth and Induces Oxidative Stress in Roots. Annals of Botany 98(6): 1261 – 1269
doi.org/10.1093/aob/mc1213
Soln, K., Znidarsic, N. and Koce, J. D. 2022 Root Growth Inhibition and Ultrastructural Changes in Radish Root Tips after Treatment with Aqueous Extracts of Fallopia japonica and F. xbohemica Rhizomes. Protoplasma 259(2): 343 – 355
doi: 10.1007/s00709-021-01668-4
Thiebaut, G., Tarayre, M. and Rodriguez-Perez, H. 2019 Allelopathic Effects of Native Versus Invasive Plants on One Major Invader. Front. Plant Sci. 10: 854
doi: 10.3389/fpls.2019.00854
Vivanco, J. M., Bais, H. P., Stermitz, F. R., Thelen, G. C. and Callaway, R. M. 2004 Biogeographical Variation in Community Response to Root Allelochemistry: Novel Weapons and Exotic Invasion. Ecology Letters 7(4): 285 – 292
doi.org/10.1111/j.1461-0248.2004.00576.x
Wardle, D., Nilsson, M-C. and Gallet, C. 2007 An Ecosystem-Level Perspective of Allelopathy. Biological Reviews of the Cambridge Philosophical Society 73(3): 305 – 319
doi: 10.1111/j.1469-185X.1998.tb00033.x
Weston, L. A. and Duke, S. O. 2003 Weed and Crop Allelopathy. Critical Reviews in Plant Sciences 22(3-4): 367 – 389
doi.org/10.1080/713610861
Zeng, R. S. 2014 Allelopathy-The Solution is Indirect. J. Chem. Ecol. 40: 515 – 516
doi: 10.1007/s10886-014-0464-7
Zeng, R. S., Luo, S. M., Shi, Y. H., Shi, M. B. and Tu, C. Y. 2001 Physiological and Biochemical Mechanism of Allelopathy of Secalonic Acid F on Higher plants. Agronomy J. 93(1): 72 – 79
doi.org/10.2134/agronj2001.93172x
Zhang, S., Jin, Y., Tang, J. and Chen, X. 2009 The invasive plant Solidago canadensis L. Suppresses Local Soil Pathogens through Allelopathy. Applied Soil Ecology 41(2): 215 – 222
doi.org/10.1016/j.apsoil.2008.11.002
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