The process by which a plant acquires more of the available resources such as nutrients, water or light from the environment without any chemical action on the surrounding plants is called resource competition.
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This process is not negative allelopathy, although both processes can act together to enhance the survival rate of the plant species. The term allelopathy from the Greek -derived compounds allelo- and -pathy meaning "mutual harm" or "suffering" , was first used in by the Austrian professor Hans Molisch in the book Der Einfluss einer Pflanze auf die andere - Allelopathie The Effect of Plants on Each Other - Allelopathy published in German.
Long before the term allelopathy was used, people observed the negative effects that one plant could have on another. Theophrastus , who lived around BC noticed the inhibitory effects of pigweed on alfalfa.
In China around the first century AD, the author of Shennong Ben Cao Jing described plants that had pesticidal abilities, including those with allelopathic effects. Allelopathy is not universally accepted among ecologists and many have argued that its effects cannot be distinguished from the competition which results when two or more organisms attempt to use the same limited resource, to the detriment of one or both. Allelopathy is a direct negative effect on one organism resulting from the input of substances into the environment by another. In the s, great effort went into distinguishing competitive and allelopathic effects by some researchers, while in the s others argued that the effects were often interdependent and could not readily be distinguished.
However, by D. Liu and J. Lowett at the Department of Agronomy and Soil Science, University of New England in Armidale, NSW, Australia wrote two papers   in the Journal of Chemical Ecology that developed methods to separate the allelochemical effects from other competitive effects, using barley plants and inventing a process to examine the allelochemicals directly. The possible application of allelopathy in agriculture is the subject of much research.
For example, Leptospermone is a purported thermochemical in lemon bottlebrush Callistemon citrinus. Although it was found to be too weak as a commercial herbicide, a chemical analog of it, mesotrione tradename Callisto , was found to be effective.
Allelopathy: Current status of research and future of the discipline: A commentary
Sheeja reported the allelopathic interaction of the weeds Chromolaena odorata Eupatorium odoratum and Lantana camara on selected major crops. Many crop cultivars show strong allelopathic properties, of which rice Oryza sativa has been most studied. More recently, critical review on rice allelopathy and the possibility for weed management reported that allelopathic characteristics in rice are quantitatively inherited and several allelopathy-involved traits have been identified.
Many invasive plant species interfere with native plants through allelopathy.
One of the most widely known early examples was Salvia leucophylla , because it was on the cover of the journal Science in However, like many allelopathy studies, it was based on artificial lab experiments and unwarranted extrapolations to natural ecosystems. In , Science published a study where caging the shrubs to exclude rodents and birds allowed grass to grow in the bare zones. Allelopathy has been shown to play a crucial role in forests, influencing the composition of the vegetation growth, and also provides an explanation for the patterns of forest regeneration. The black walnut Juglans nigra produces the allelochemical juglone , which affects some species greatly while others not at all.
Phenolics and Plant Allelopathy
The leaf litter and root exudates of some Eucalyptus  species are allelopathic for certain soil microbes and plant species. The tree of heaven , Ailanthus altissima , produces allelochemicals in its roots that inhibit the growth of many plants. Francisco A. Macias , Juan C. Galindo , Jose M. Most, if not all, books on allelopathy cover the ecological, agronomic, and descriptive physiological aspects.
Practically, the allelopathy can be exploited in organic farming in understanding and identifying compatibility between species, to finding natural substances with herbicide potential. In experiments conducted, diluted extracts of Taraxacum officinale and Cirsium vulgare strongly inhibited the germination and growth of corn and beans, while Hedera helix produced the same effect, but at higher concentrations of the extract. Humulus lupulus extract has a stimulating effect on the two species and it is possible to use as natural fertilizer.
Extracts of Chenopodium album works as stimulator for Beta vulgaris , and potent inhibitor for Triticum aestivum. Agropyron repens is an aggressive competitor for Lycopersicon esculentum and Capsicum annuum , producing a strong inhibition.
Proving Allelopathy in Crop–Weed Interactions
Juglans regia extracts and especially those of Satureja hortensis , can be used as natural herbicides for up delay germination and growth suppression for the species: Echinochloa crus-galli and Setaria glauca. Content from this work may be used under the terms of the Creative Commons Attribution 3. Any further distribution of this work must maintain attribution to the author s and the title of the work, journal citation and DOI. Crossref Google Scholar. Google Scholar.