Review of Plant Defense Mechanisms

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 than 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 morph...

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