Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2007
Publication Date: 2/1/2008
Citation: Rolshausen, P.E., Greve, L.C., Labavitch, J.M., Mahoney, N.E., Molyneux, R.J., Gubler, W.D. 2008. Pathogenesis of Eutypa lata in grapevine: Identification of virulence factors and biochemical characterization of cordon dieback. Journal of Phytopathology.98:222-229. Interpretive Summary: The fungus Eutypa lata causes a disease in grapevines known as "dying-arm disease" in which one of the cordons (arms) of the grapevine gradually dies back, resulting in reduced grape yield. The exact way in which the fungus causes this gradual, progressive withering has not been known. This research shows that structural components with a high content of the sugar, glucose, are destroyed by the fungus and that the Merlot grape variety has more resistance than Cabernet Sauvignon because of a higher level of lignin, the woody tissue responsible for the strength of branches and trunks of trees and shrubs. This information may allow new varieties of grapevines to be chosen with fundamental resistance to breakdown by the fungus.
Technical Abstract: Eutypa lata is a vascular pathogen of woody plants. In the present study we (i) determined which component(s) of the cell wall polymers were degraded in naturally infected grapevines and in artificially inoculated grape wood blocks; (ii) compared the pattern of wood decay in the tolerant grape cultivar Merlot vs. the susceptible cultivar Cabernet Sauvignon; and (iii) identified secondary metabolites and hydrolytic enzymes expressed by E. lata during wood degradation. Biochemical analyses and cytochemical study indicated that glucose-rich polymers were primary targets of E. lata. Structural glucose and the hemicellulose fraction of the plant cell wall as well as starch were depleted in infected woods identically in both cultivars. Moreover, the more tolerant cultivar Merlot always had more lignin in the wood than the susceptible cultivar Cabernet Sauvignon, indicating that this polymer may play a role in disease resistance. In vitro assays demonstrated the production by E. lata of oxidases, glycosidases and starch degrading enzymes. Phytotoxic secondary metabolites were also produced but our data suggest that they may bind to the wood. Finally, we demonstrated that free glucose in liquid cultures repressed primary but not secondary metabolism.