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Submitted to: Internet Conference on Phytopathogenic Mollicutes
Publication Type: Proceedings Publication Acceptance Date: 7/1/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Phytoplasmas and spiroplasmas are two kinds of unique microbes that cause diseases worldwide in plants that include ornamentals, food, feed, oil, and fiber crops, weeds, and forest trees. These microbes are unusual in that they are surrounded only by a single membrane and have no cell wall. Both kinds are transmitted from plant-to-plant by insects (leafhoppers) that suck plant sap. Before 1967, the plant diseases caused by phytoplamas and spiroplasmas were mistakenly assumed to be caused by viruses. Since 1967, much progress has been made in understanding these microbes and the diseases that they cause, but much remains to be learned. This paper poses questions and forms hypotheses and theories that are destined for future research. The paper will be of interest to specialists in bacteriology, as well as students and biologists interested in what the future may hold for research on a group of unique cellular pathogens. Technical Abstract: Little more than three decades have passed since the long sought pathogens of plant "yellows diseases" were found to be prokaryotic cellular microbes, and not viruses as had been universally presumed in the scentific community for more than four decades prior to 1967. This landmark discovery launched a wordwide renaissance, in which research on numerous plant diseases of unsolved cause was pursued with renewed enthusiasm. The discovery of mycoplasmalike organisms (MLOs)s as the probable cause of plant "yellows diseases" in 1967 was followed by a steady growth in knowledge of these unique microbes and their relatives (members of the class Mollicutes). This growth has been punctuated by the discovery that cell wall-less prokaryotes infecting plants were of two distinct types, mycoplasmalike organisms (MLOs) and spiroplasmas; by the isolation of spiroplasmas in culture, proof of their plant pathogenicity, and description of over 30 Spiroplasma species, many from insects; by discoveries of MLOs as the probable causes of "yellows" diseases worldwide in more than 300 plant species; by recognition of the evolutionary position of MLOs within the class Mollicutes, determination that MLOs comprise a monophyletic clade in the class, and acceptance of the term phytoplasma for members of the clade; by the development of rapid and sensitive means for phytoplasma detection and identification; by the construction of schemes for classification of phytoplasmas based on molecular data; by the emergence of a provisional phytoplasma taxonomy and the designation of "Candidatus Phytoplasma species"; by new knowledge gained about the ecology and molecular biology of spiroplasmas; and by other developments of which many will be reported in this Internet Conference. |
