New Directions for Biosciences Research in Agriculture High-Reward Opportunities (1985) / Chapter Skim
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5. Plant Diseases and Insect Pests
5. Plant Diseases and Insect Pests
Pages 81-104
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From page 81... ...
mat is, because of a lack of basic information about the function of genes for resistance, studies are often random rather than specifically targeted explorations. In addition, any results can be short-lived because of the changing nature of pathogens and other pests as new genetic information is introduced into complex agro-ecol ogical systems.
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From page 82... ...
An increased understanding of insect neurobiology and the chemistry and action of modulating substances, such as the endocrine hormones that regulate metamorphosis, diapause, and reproduction, will open new avenues for controlling insect pests by disrupting their physiology and behavior at critical stages in the life cycle.
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From page 83... ...
Understanding the molecular bases that determine this specificity in recognition or in the pathogen's ability to alter the host's metabolism should yield new, definitive, and more efficient ways to prevent attacks on crop plants or to mitigate disease symptoms. Based on our current, limited understanding of the types of interactions that occur between host plants and pathogens, the mechanisms involved are varied and complex.
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From page 84... ...
With respect to plant viruses the term resistance is used rather loosely. Quite often only the appearance of disease symptoms is considered.
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From page 85... ...
Genetics Continued breeding studies and genetic analysis of resistance traits in host plants and virulence traits in pathogens provide the experimental systems needed to isolate and determine the properties of recognition molecules involved in susceptibility or active resistance, such as phytoalexin biosynthesis. Single-gene changes that confer resistance against a pathogen exist and are used in crop breeding to develop improved cultivars.
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From page 86... ...
This exposure somehow induces resistance properties so that when the plant is subsequently challenged by one or more pathogenic strains, it will resist infection or exhibit only mild disease symptoms. Acquired resistance is most actively being studied using Pseudomonas solanacearum, some strains of which cause wilt and stem rot in tobacco, ginger, potato, tomato, and banana.
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From page 87... ...
This gene should be the one responsible for inducing the hypersensitive lesion. Gene Transfer The ultimate goal of research discussed in this section on genetics, gene products, and gene structure is the routine transfer and expression of genes for resistance in agriculturally useful plants.
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From page 88... ...
Easily observable disease symptoms, such as chlorosis, necrosis, and cellular growth distortions, can have a number of diverse causes. Therefore, it is not possible to make progress on such generalized disease symptoms without some indication of the kinds of pathogens involved.
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From page 89... ...
If the DNA clones themselves are not infectious, the cloned viral or viroid DNA can be transcribed back to RNA using any of several in vitro systems. Thus, sitespecific modifications made in the DNA clone can be transcribed into the RNA to test the effect of such changes on infectivity and disease symptoms.
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From page 90... ...
Other bacterial metabolites appear to have specific effects on host plant species. charides, which are associated with wilting of plants, can be released in amounts great enough to clog up transport between plant cells, and may act by disrupting plant cell membrane functions.
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From page 91... ...
To strengthen programs in the molecular basis of plant diseases, research investigations should emphasize: The molecular bases of the factors that determine whether a host-pathogen pair will result in a resistant or a susceptible interaction. · me basic concepts of the interaction between the host and the invading pathogen that result in disease.
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From page 92... ...
the development of genetically engineered microorganisms to remove organic pesticide residues, such as herbicides. Microbial Agents for Biological Control Little commercialization of microorganisms for biological control has been done.
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From page 93... ...
Control of Pathogens The proven feasibility of using biological control in this area has spurred research. m e bacterium Agrobacterium radiobacter is commercially used to prevent infection of susceptible plants by a related bacterium, A
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From page 94... ...
Control of Nematodes Control of plant parasitic nematodes has been largely accomplished through the use of chemical nematocides, many of which have now been shown to be harmful to the environment and have been withdrawn from use. Biological control measures using resistant plant varieties and trap crops have been effective in some cases.
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From page 95... ...
Biological Degradation of Organic Pesticides Timely and appropriate disposal of pesticide residues in water and soils is an important and attainable goal in routine agricultural production practices. The biological degradation of pesticides is theoretically feasible.
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From page 96... ...
Further, the agency should seek conventional genetic or recombinant-DNA technologies to make these agents more effective; · Generating more knowledge of the basic biology of plant pathogenic nematodes to develop novel, nonpesticide means of control by perturbing reproduction and development; and · Developing unique microorganisms that will promote plant health and others that can be used to detoxify or destroy organic pesticide pollutants. Molecular Basis of Pesticide Action Pesticides are major tools in the production of food and fiber and in the maintenance of high standards of veterinary, human, and plant health.
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From page 97... ...
me molecular basis for metabolic activation and detoxification must be defined. Using this background knowledge genetic engineering can provide opportunities for modifying receptor sites and detoxification mechanisms for improved animal and crop safety.
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From page 98... ...
More specifically, the ARS should emphasize: Definition of the molecular basis for metabolic activation and detoxification of pesticides; Study of new targets for selective pesticide action; Identification of new natural chemicals important in regulating pest populations; Investigation of the basic molecular biology of vectors for gene transfer and elucidation of gene regulation in insects; and Continued research on both insect genetics and on natural products chemistry. Insect Neurobiology and the Regulation of Development and Reproduction The functional responsiveness of an insect is dependent on rapid chemical communications among its own cells and between the individual and other insects.
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From page 99... ...
Such studies will also define the mechanisms by which the central nervous system integrates and regulates these processes. This understanding may allow scientists eventually to selectively manipulate the neuroendocrine system, and thus control insects by altering their ability to fly, curtailing metamorphosis, or disrupting sexual recognition.
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From page 100... ...
Knowledge gained from such a fundamental research program in insect neurobiology could be used in conjunction with genetic engineering methodologies to investigate the basic molecular biology of vectors for gene transfer and to elucidate gene regulation in insects. These new technologies could also aid in mapping the insect genome, particularly the genes for regulatory peptides.
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From page 101... ...
Thus, basic research is needed to identify and chemically characterize insect hormones and to define at the molecular level both their physiological function and their mechanism of action. Although some insect hormones, such as the sesquiterpenoid juvenile hormones and the ecdysteroids, have been intensively investigated, the extent of their involvement in regulating insect development and reproduction is only now being realized.
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From page 102... ...
Bacteria and other microorganisms producing insecticidal materials and the plant itself may also be modified by selection and genetic engineering to increase the impact of natural toxicants or feeding deterrents in host-insect pest interactions. Further development of insect cell cultures and vectors for gene transfer in insects may permit the introduction of deleterious effects into pest populations.
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From page 103... ...
While most of the research skills necessary for a major program in insect neurobiology -- chemistry, neurophysiology, behavior, biophysics, and physiology -- are already in place within the ARS, additional expertise in neurochemistry, peptide chemistry, and biochemistry (mechanistic aspects or chemical regulation) , and immunology must be added.
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From page 104... ...
104 research at a single site, preferably near a university or another research institute that has a strong program in neurobiology. ARS research should specifically focus on the following: · Chemistry of the brain factors that control pheromone production and release, and their mechanisms of action; · Neural regulation of the synthesis, processing, and secretion of cerebral pheromonotropic peptides; · The endocrine basis of insect reproduction, in particular, identification of the cerebral neuropeptides involved and their target glands, and identification of the mechanisms regulating these glands; · Mechanisms that regulate the synthesis of ecdysteroids and juvenile hormones, and the biosynthetic pathways of these two hormome families; and · Interhormonal endocrine feedback; regulation of insect growth, development, and reproduction; and the roles and molecular mechanisms of the principal developmental hormones in regulating one another's synthesis.
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