Author
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Lulai, Edward |
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Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/12/2005 Publication Date: 11/1/2005 Citation: Lulai, E.C. 2005. Non-wound induced Suberization of Tuber Parenchyma Cells: A Physiological Response to the Wilt Disease Pathogen Verticillium Dahliae. American Journal of Potato Research. 82(6):433-440. Interpretive Summary: Wilt pathogens create serious yield and quality problems in the potato crop. These pathogens (Verticillium spp.) enter the root and eventually penetrate the vascular/circulatory system where they can further spread throughout the growing plant. The infected vasculature of the growing plant becomes plugged with cellular debris thus killing the plant. The pathogen may also spread into the vessels of the vascular tissue of the potato tuber. The vasculature of infected potato tubers often become discolored creating a serious market quality defect that prevents sale of raw product to its primary market. Despite the losses and disease issues created by these infections, the physiological responses to colonization of tuber vessel elements are poorly described, and a model system to study these responses in the laboratory has not been developed. In the research reported here, a model system was developed and tested to determine if tuber vessel elements could be infiltrated with test pathogen in a laboratory setting and if a detectable physiological response could be elicited and identified. Results demonstrated that tuber vessel elements in the model system could be infiltrated, and that infiltration of the wilt pathogen, Verticillium dahliae Kleb., induced a suberization response on the walls of neighboring parenchyma cells. Plants form suberin as a natural durable barrier to infection. The suberization response was determined by assessing the accumulation of two major biopolymers that comprise suberin; polyaliphatics and polyphenolics. A similar suberization response was found in tubers that had been naturally infected in the field. This simple model system provides a versatile tool to investigate the physiological responses of potato tuber to colonization of vessel elements and resist spread of the disease. This process of suberization occurred inside the tuber without a wound stimulus. Postharvest wounding is known to cause potato tuber cells to form a suberin layer as part of the healing process and to protect against infection. However, in these experiments, the signal to initiate suberin formation was derived from the plant-pathogen interaction. We believe this to be the first report for such a physiological response to Verticillium spp. in potato tuber. Technical Abstract: Wilt pathogens (Verticillium spp.) enter the root and eventually penetrate xylem vessels where they can spread into the vascular tissue of the potato tuber. Infected tuber vessel elements often become discolored creating a serious market quality defect that prevents sale of raw product to its primary market. Despite the losses and disease issues created by these infections, the physiological responses to colonization of tuber vessel elements are poorly described, and a model system to study these responses in the laboratory has not been developed. In the research reported here, a model system was developed and tested to determine if tuber vessel elements could be infiltrated in a laboratory setting and if a detectable physiological response could be elicited. Results demonstrated that tuber vessel elements in the model system could be infiltrated, and that infiltration of Verticillium dahliae Kleb. conidia, induced a suberization response on the walls of neighboring parenchyma cells. Unlike tomato petioles where the xylem vessel walls appeared to accumulate suberin, tuber vessel elements are not capable of suberizing. The suberization response was determined for accumulation of suberin polyaliphatics and polyphenolics. A similar suberization response was found in tubers that had been naturally infected in the field. This simple model system provides a versatile tool to investigate the physiological responses of potato tuber to colonization of vessel elements. This process of internal suberization occurred without wound-induction of the cells. Consequently, the signal was derived from the plant-pathogen interaction. We believe this to be the first report for such a physiological response to Verticillium spp. in potato tuber. |
