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This 10-page paper discusses about plant defense mechanisms. It consists of an abstract, introduction, mechanisms of defense against insects and pathogens, disease resistance genes, biotechnologies, case studies and future research and practical applications.
An imperiled plant is somewhat like a person. It has to depend on the defense mechanisms, both structural and metabolic to prevent harmful effects of the pathogens. It includes preexisting defense structures surface waxes, structure of epidermal cell walls, position of stomata and lenticles, thick cell walls, leaf hairs, defense structures formed in response to infection by the pathogen, histological defense structures, metabolic (biochemical) defense preexisting biochemical defense, metabolic defense induced by the attacking pathogen, defense through the hypersensitive reaction, defense through increased levels of phenolic compounds, "common" phenolics etc. Plants also activate a specific set of defense genes in response to assault. Recent technologies have enabled us to have plants with "useful genes" only, thus providing better crops in larger number. Unlike traditional plant breeding, which involves the crossing of hundreds or thousands of genes, plant biotechnology allows for the transfer of only one or a few desirable genes. This more precise science allows plant breeders to develop crops with specific beneficial traits and without undesirable traits. Many of these beneficial traits in new plant varieties fight plant pests -- insects, disease and weeds -- that can be devastating to crops. Others provide quality improvements, such as tastier fruits and vegetables; processing advantages, such as tomatoes with higher solids content; and nutrition enhancements, such as oil seeds that produce oils with lower saturated fat content.
An imperiled plant is somewhat like a person. It, too, relies on built-in safety mechanisms to ensure its well-being. While it can't exactly flee an imminent threat - such as from disease-causing bacteria or a hungry insect - it can fight back. First, however, the plant must know what it is up against.
The success of a disease interaction, whether from the point of view of the surviving plant or of the victorious pathogen, depends on mechanisms of evolution. Mechanisms of genetic exchange and adaptive evolution are intertwined to provide plants with a supply of newly divergent R-gene alleles, with new pathogen specificities.
The stakes in this battle against plant diseases are high, because a huge portion of agricultural production is lost to pathogen and pest damage. In compensation, farmers plant more land. The implications are far-reaching: Not only are more land and labor used by agriculture, but more water is also needed --so much more that in regions where water is scarce, it may be worthwhile to address plant disease as a way to conserve on water usage.
It is important to realize that plant defense can have important impacts:
Alstad & Edmunds / Alstad & Corbin's work on black pineleaf scale insects has demonstrated that adjacent trees may differ greatly in their defensive chemistry. However, the scale insects' sedentary lifestyle allows them to produce populations that are adapted to the chemistry of individual trees and even branches upon trees.1
Hunter's (1995) meta-analysis of lepidoptera reveals that spring-feeding species are more likely to be wingless than those that feed in summer. This is argued to be an adaptation to matching the phenology of bud break in genetically variable trees. Feeny's (1970) classic study illustrated the detrimental impacts of missing bud break in oak trees. Hamrick (1984) has argued that long-lived trees are among the most genetically variable organisms on earth.
All plants must assume forms that allow certain metabolic functions to take place, including photosynthesis, and orderly growth. But in addition, some plants have acquired morphological adaptations that make them at least partially resistant to insect predation. Examples of Morphological Traits that Confer Crop Resistance
Certain colors are less attractive to certain insects. For example, imported cabbage worm is less attracted to red colored Brassica species (cabbages, broccoli, and related species). Cucumber beetles do less damage on reddish colored varieties of leaf lettuce and are attracted to certain hues of yellow. Some birds prefer red plums to green plums.
While it is impossible to generalize what shapes resist predation better, shape does play a role in avoiding predation. For example, one study noted that turnip maggots less damaged thick rooted turnips. Another study showed that onions with leaves having a narrow angle of contact are more attractive to thrips than onion varieties with looser leaves. 3
Thickening of cell walls and/or rapid growth:
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Terminology mentioned in this research paper
biotechnology industry, fatty acids, food supply,
Names mentioned in this paper
Plants, Jacyn Baker, Hamrick, Hunter, Edmunds, Feeny, L.) Moench, Clavey, Corbin, Arnold Red, Alstad,
Organizations referenced in this term paper
Pathogen Defense, National Research Council,
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Keywords talked about in this report
plant, insect, plant defense, plant biotechnology, pathogen, crops, plant disease, plant breeding, phenolic compounds, plant breeders, cell wall, Plant Disease Resistance, the plant, diseases, Molecular Plant Pathology, plant species, plant cell, plant pathologist, metabolic, pest, European white birch, Resistance Color, acid, biochemical, sorghum, infection, jasmonic acid, saturated fat, predation, red color, bud break, oil seeds, case studies, gene, evolutionary biology, aphid, signal transduction pathway, imported cabbage worm, toxins, bronze birch borer, mutants, traditional, Corn varieties, Sorghum bicolor, cabbage, metabolism, onions, phenolics, phenols, leaf,