Fungi used as a Herbicide
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| - | [[Image:vineyardweed.jpg|center|Various Vineyard Weeds]] | ||
| ==Introduction== | ==Introduction== | ||
| + | [[Image:vineyardweed.jpg|center|Various Vineyard Weeds]] | ||
| The presence of weeds can result in the loss of up to half of a grower’s expected crop yield. The lost yield results in economic losses which is a problem in the agriculture industry. Fungi can be used as a herbicide to gain control of weeds and solve this issue. Fungal herbicides have been legal in Canada since 1973 <ref name="Misra"> Misra, H.P. Weed Management Through Fungal Herbicides. (2005) Orissa Review. 53-56</ref>. In order to use a fungus for this purpose, a [http://en.wikipedia.org/wiki/Mycoherbicide mycoherbicide] is created with the fungi as its active ingredient. This mycoherbicide must be able to inhibit weed growth without harming the crop or the living things surrounding it. A benefit is that the fungi used are host specific and will reside on the soil or weed host, while a commercial chemical herbicide would need to be reapplied to the crop. Certain mycoherbicides work better on certain strains of weeds because of the resistance of the plant in combatant with the virulence factors of the pathogen. There are currently 37 mycoherbicides and 8 techniques of applying them <ref name="Misra"/>. The fungi species most commonly used as herbicides in North America are ''Collectrichum gloeosporioides'' (Collego®) and ''Phytophthora palmivoraa'' (De Vine®)<ref name="Misra"/>. . There are different ways for the pathogen to infect the host, two main ways that will be covered are spore germination causing infection as well as phytotoxins<ref name="Misra"/>. | The presence of weeds can result in the loss of up to half of a grower’s expected crop yield. The lost yield results in economic losses which is a problem in the agriculture industry. Fungi can be used as a herbicide to gain control of weeds and solve this issue. Fungal herbicides have been legal in Canada since 1973 <ref name="Misra"> Misra, H.P. Weed Management Through Fungal Herbicides. (2005) Orissa Review. 53-56</ref>. In order to use a fungus for this purpose, a [http://en.wikipedia.org/wiki/Mycoherbicide mycoherbicide] is created with the fungi as its active ingredient. This mycoherbicide must be able to inhibit weed growth without harming the crop or the living things surrounding it. A benefit is that the fungi used are host specific and will reside on the soil or weed host, while a commercial chemical herbicide would need to be reapplied to the crop. Certain mycoherbicides work better on certain strains of weeds because of the resistance of the plant in combatant with the virulence factors of the pathogen. There are currently 37 mycoherbicides and 8 techniques of applying them <ref name="Misra"/>. The fungi species most commonly used as herbicides in North America are ''Collectrichum gloeosporioides'' (Collego®) and ''Phytophthora palmivoraa'' (De Vine®)<ref name="Misra"/>. . There are different ways for the pathogen to infect the host, two main ways that will be covered are spore germination causing infection as well as phytotoxins<ref name="Misra"/>. | ||
Revision as of 00:34, 22 March 2013
Contents |
Introduction
The presence of weeds can result in the loss of up to half of a grower’s expected crop yield. The lost yield results in economic losses which is a problem in the agriculture industry. Fungi can be used as a herbicide to gain control of weeds and solve this issue. Fungal herbicides have been legal in Canada since 1973 [1]. In order to use a fungus for this purpose, a mycoherbicide is created with the fungi as its active ingredient. This mycoherbicide must be able to inhibit weed growth without harming the crop or the living things surrounding it. A benefit is that the fungi used are host specific and will reside on the soil or weed host, while a commercial chemical herbicide would need to be reapplied to the crop. Certain mycoherbicides work better on certain strains of weeds because of the resistance of the plant in combatant with the virulence factors of the pathogen. There are currently 37 mycoherbicides and 8 techniques of applying them [1]. The fungi species most commonly used as herbicides in North America are Collectrichum gloeosporioides (Collego®) and Phytophthora palmivoraa (De Vine®)[1]. . There are different ways for the pathogen to infect the host, two main ways that will be covered are spore germination causing infection as well as phytotoxins[1].
Virulence Factors
Virulence factors are characteristics of organisms that allow organisms to be more or less infectious. These factors can include spectrum of host, dispersal of spores, adhesive abilities, and other evolutionary advances that give it an edge on infecting hosts. In terms of organisms the higher the virulence factors then the more likely the organism is to infect more hosts and be more effective. This is especially true for the class of fungi called Rusts(). The reasons that Rusts have a high virulence factors is because of the five different types of spores throughout its life cycle, the long distance dispersal of those spores, the adhesive abilities and the broad species of hosts(). This allows Rusts to be very virulent as a mycoherbicide because there are many plants that are susceptible to infection from Rusts. Virulence factors can be considered two of the sides of the disease triangle. The two sides were pathogen and host infected.
Process
Mycoherbicides act by releasing phytopathogens to suppress weed growth. The phytopathogens release phytotoxins that can kill weeds in up to five weeks time [1]. The pathogens released have the ability to produce spores for asexual reproduction and are tested to be stable and temperature tolerant. Fungal herbicides are easily made once the anti-herb properties have been testing as well as the living conditions for that fungus. They are easily applied by spraying. Once applied, the spores will germinate and penetrate the herb tissue and the phytotoxins will start to work. However, there are reasons fungal herbicides may not be used in place of a harmful chemical. In North America, fungal herbicides have to be registered and approved by the Environmental Protection Agency (EPA) which can take years [2]. The anti-herb capacity of fungi is generally less than that of a chemical herbicide. Fungal herbicides are not commonly used because their success rate depends on the environmental conditions and because they are so host specific.
Other ways that a mycoherbicide can infect its host are through physical infection via the germination of a spore. This process happens when a spore lands on a leaf of a plant that it can infect. A germ tube is used to infect the upper layers of the leaf, and then an appressoria is created. This appressoria is the place of infection where the spore then can stay adhered to the leaf. The infection then starts from there, and goes outwards from there (). Other ways of infection is that the fungi covers the stoma with the appressoria, leaving the stoma lodged open for more infections to become present(). This is a very complicated and expertise way of creating an infection for a pathogen because of all the working parts that go into the infection.
Phytotoxins
Phytotoxins are low molecular weight secondary metabolites that cause plant disease. In this case, the plant being infected is a weed plant. Phytotoxins may also be responsible for visual symptoms of disease such as wilting or necrosis. A common phytotoxin found in the fungi species Penicillium is vulculic acid [2]. Vulculic acid works against weeds by increasing leaf membrane permeability, inducing lipid peroxidation and damaging the cell membrane [2]. Phytotoxins have a limited stable state because of their short half-life and sensitivity to the environment. Phytotoxins are difficult to produce for commercial sale because they are produced in very small quantities by fungi and difficult to isolate [2].
Plant Resistance
Plants can resist fungi through many ways, based upon the qualities that the plants have. This is related to one of the sides of the disease triangle, the host side. If the host has the ability to reject or break down the invading process than an infection will not persist. The genome of the plant, allows for only a small amount of pathogens to infect them, therefore infection has to be particular leaving herbicides to be a little less complicated. There are three ways that plants inhibit the infection of pathogens:
- The pathogen is completely out of the host range, and it has no affect on the plants because of the two different genomes
- The plant has specific resistance genes to that of the pathogen
- The plant can tolerate or escape the infection itself
Other ways that plants can protect themselves from infection is through their own use of protective methods. An example of one of these methods include the use of toxic chemicals or antifungal chemicals that break down infected cells, riding the plant of the pathogen().
Arrowhead
A specific weed strain commonly known as arrowhead (Sagitaria trifolia) is the cause of the largest rice plantation problem in Iran [3]. Arrowhead is notably resistant to chemical herbicides. Collego® is used in the USA as the solution to arrowhead [3]. The fungi Alternaria pellucida was tested and proved that it could successfully be used as a mycoherbicide against arrowhead in Iran. This fungi works by preventing early growth of the weed. The fungi species was tested for its anti-herb properties on three indigenous cultivars of rice, two bred cultivars and lastly on an arrowhead infested cultivar, all cultivated separately in a greenhouse [3]. Alternaria pellucida significantly altered the height of the arrowhead weed and was concluded to be a mycoherbicide able to control the arrowhead weed [3].
Puccinia romagrolia Marie & Sacc.
This species of Puccinia is the bioherbicide that infects and kills the species of
Notes and References
- ↑ 1.0 1.1 1.2 1.3 1.4 Misra, H.P. Weed Management Through Fungal Herbicides. (2005) Orissa Review. 53-56
- ↑ 2.0 2.1 2.2 2.3 Duan, G.F., Yu, L.Q., Zhang, J.P. and Zhou, Y.J. Fungal phytotoxins for weed management. (2011) International Allelopathy Foundation. 27(1): 1-14
- ↑ 3.0 3.1 3.2 3.3 Javadzadeh, Armin and Motlagh, M. Study of Alternaria pellucida as a promising mycoherbicide for controlling Arrowhead (Sagitaria trifolia) in paddy fields (2010) POJ 3(6):172-176
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