سایت تخصصی علوم کشاورزی و زیستی

سایت تخصصی علوم کشاورزی و زیستی
مطالب و مقالات علمی در زمینه های مختلف علوم کشاورزی و زیستی(خوش آمدید)


Allelopathy  is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms. Allelochemicals are a subset of secondary metabolitesُ which are not required for metabolism (i.e. growth, development and reproduction) of the allelopathic organism. Allelochemicals with negative allelopathic effects are an important part of plant defense against herbivory.

Allelopathy is characteristic of certain plants, algae, bacteria, coral, and fungi. Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of many invasive plants. For specific examples, see Spotted Knapweed (Centaurea maculosa), Garlic Mustard (Alliaria petiolata), and Nutsedge.

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. This process is not negative allelopathy, although both processes can act together to enhance the survival rate of the plant species.

Examples of allelopathy

The possible application of allelopathy in agriculture is the subject of much research. Current research is focused on the effects of weeds on crops, crops on weeds, and crops on crops. This research furthers the possibility of using allelochemicals as growth regulators and natural herbicides, to promote sustainable agriculture. A number of such allelochemicals are commercially available or in the process of large-scale manufacture. 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.

 It is sold to control broadleaf weeds in corn but also seems to be an effective control for crabgrass in lawns. Sheeja (1993) 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.

 Rice allelopathy depends on variety and origin: Japonica rice is more allelopathic than Indica and Japonica-Indica hybrid. 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. A famous case of purported allelopathy is in desert shrubs. One of the most widely known early examples was Salvia leucophylla, because it was on the cover of the journal Science in 1964. Bare zones around the shrubs were hypothesized to be caused by volatile terpenes emitted by the shrubs. However, like many allelopathy studies, it was based on artificial lab experiments and unwarranted extrapolations to natural ecosystems. In 1970, Science published a study where caging the shrubs to exclude rodents and birds allowed grass to grow in the bare zones. A detailed history of this story can be found in Halsey 2004.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. Eucalyptus leaf litter and root exudates 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. The pace of evaluating allelochemicals released by higher plants in nature has greatly accelerated, with promising results in field screening.Garlic mustard is an invasive plant species in North American temperate forests. Its success may be partly due to its excretion of an unidentified allelochemical that interferes with mutualisms between native tree roots and their mycorrhizal fungi.A study of Kochia scoparia in northern Montana by two high school students showed that when Kochia precedes spring wheat (Triticum aestivum), it reduces the spring wheat's growth. Effects included delayed emergence, decreased rate of growth, decreased final height and decreased average vegetative dry weight of spring wheat plants. A larger study later showed that Kochia seems to exhibit allelopathy on various crops in northern Montana.Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass, which reduces germination of many broadleaf and grass weeds.



[ یکشنبه 25 دی1390 ] [ 11:39 PM ] [ مهندس پیمان جعفری ] [ ]
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مهندس پیمان جعفری_ کارشناس علوم زراعت و اصلاح نباتات"عضو انجمن های علوم زراعت و اصلاح نباتات و بیوتکنولوژی ایران"
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