ISHS Acta Horticulturae 36: III International Symposium on Virus Diseases of Ornamental Plants
DETECTION OF VIRUSES AND DIAGNOSIS OF PLANT VIRAL DISEASES BY ELECTRON MICROSCOPY |
| Author: | M.K. Corbett |
| Abstract:
The first commercial electron microscope was offered by Siemens and Halske Co. in 1939. The political unrest immediately following that time, however, interferred with the extensive use of the electron microscope in the field of biology. The quality of electron micrographs of plant viruses made in the early 1940's was not very exciting by todays standards, but I am sure that investigators at that time were elated over seeing any form, rod or sphere, that they could associate with the infectious agent called a virus (Stanley and Anderson, 1941). Improved resolution of the instrument and enhanced specimen contrast provided by the shadow cast technique gave incentive to the use of the instrument in virology (Williams and Wyckoff, 1945). Additional structural detail of virus particle morphology was made possible by the technique of negative staining described by Hall (1955) and popularized by Brenner and Horne (1959). Techniques for observing virus particles by electron microscopy were readily available but they were used mainly with purified preparations. The use of the electron microscope for detecting viruses in unpurified preparations was not readily accepted even after Johnson (1948) published his exudate method for observing viruses in crude preparations. In 1957, the late Dr. J. Brandes developed the simple and quick "leaf-dip" technique for the detection in crude preparations of plant viruses with elongated particles. Dr. Brandes and co-workers (1959), utilizing the leaf-dip technique, proposed various groupings for viruses with elongated particles. Each group was distinguished on the basis of viruses with similar normal lengths from a population of particles. The leaf-dip technique, coupled with the procedures of negative staining and shadow casting, has popularized the electron microscope as an instrument for the detection of plant viruses. Use of the electron microscope for the detection of plant viruses. Use of the electron microscope for the detection of plant viruses that occur in relatively high concentration and have elongated or rod-shaped particles is a quick, easy, reliable procedure. Unfortunately, the procedure has limited value in detecting viruses that have polyhedral-shaped virus particles. If the polyhedral particles occur in sufficient concentration, they may be observed in shadow cast or negatively stained preparations. Improved techniques of specimen preparation and enhanced contrast were not the only stimulation for use of the electron microscope by plant pathologists. It would be unfair to overlook improvements made by commercial companies in the operation of the electron microscope. No longer does one have to be a physicist to operate an electron microscope. They are readily and efficiently operated by people with minimal training. So, | |
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