Author
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Davis, Robert |
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SINCLAIR, WAYNE - PLANT PATH, CORNELL UNIV |
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Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/12/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Phytoplasmas are believed to cause hundreds of serious diseases in economically important plant crops and in natural vegetation worldwide. These tiny bacteria, that have no cell wall, grow in the veins of plants and in the insects (leafhoppers) that transmit them from plant-to-plant. But, phytoplasmas cannot be isolated in laboratory culture. Therefore, molecular methods are now used to detect and identify these plant pathogenic organisms. In this paper, we discuss difficulties involved in determining which phytoplasma may be responsible for a specific plant disease. This issue is complicated by the fact that different phytoplasmas often cause identical disease symptoms in a particular plant species, and a single diseased plant can be simultaneously infected by several different phytoplasmas. Concepts presented in this manuscript will be of interest to scientists who are researching causality of plant diseases, and to diagnosticians and crop consultants whose responsibility it is to ascribe diseases to specific pathogens and to design and advise on methods for disease management. Technical Abstract: Although many plant diseases believed to be caused by phytoplasmas were described before phytoplasmal groups were delineated through molecular analyses, it is now possible to assess the relationship between phytoplasma identity/classification and specific plant diseases. Data are consistent with the hypothesis of a common ancestral origin of pathogenicity genes in many phytoplasmas and a limited repertoire of plant responses to pathogen signals. Observations are also consistent with the hypotheses that botanical host ranges of some phytoplasmas reflect specificities in transmission by vectors and/or vector feeding preferences; that phytoplasma-insect vector relationships are keys to understanding evolutionary divergence of phytoplasma lineages; that small differences in a highly conserved phytoplasmal gene may be regarded as potential indicators of separate gene pools; that the reliability or unreliability of diagnosis based on symptoms must be learned empirically, i.e. through case study, for each syndrome; and that some discrete diseases can be ascribed to phytoplasmal taxa at the 16S rRNA group level, while others are clearly associated with phytoplasma taxa below that level. |
