Interaction between the pathogen and host plants during the Pierces disease development of grapevines

• Author(s): Liu, X.; Lu, J.; Ren, Z.; Xu, X.; Yun, H.;
• Abstract: Pierces disease (PD) is a limited factor to production of non-native grapes in the southeastern United States. The disease has recently received national and international concerns due to its outbreak in California. Pierces disease is caused by a bacterial pathogen known as Xylella fastidiosa (XF) which is transmitted by leaf hoppers when they feed on grapevines. It has generally been believed that clogging the xylem vessels by XF results in the typical PD symptoms: marginal necrosis, uneven lignifications of annual canes, abscissions occurring between leaf blades and petioles, and dead shoots. However, there are many unexplained phenomenon during the course of the disease development, and the real causes of PD maybe more complicated than water deficiency. In order to better understand the mechanism of the disease development and host plant resistance to PD infection, we have been investigating the pathogenesis of XF, interactions between XF and grapevine, variations and changes of plant growth regulators among PD resistant and susceptible grapes. It appeared that the PD symptom development associated with physiological and biochemical changes of grapevines. For example, both ABA and SA levels increased during the course of PD development. In the mean time, PD infected leaves showed various abnormalities with symptoms similar to mineral nutrient imbalances such as phosphorous (P) deficiency and magnesium (Mg), manganese (Mn) and iron (Fe) toxicities. In addition, the PD infected leaves and petioles showed significantly lower levels of K and higher levels of Fe, Cu, and Zn than those non-infected ones. In a separate study, when culture filtrates from X. fastidiosa were placed on wounded leaf segment, the susceptible cultivars showed severe symptoms while no or very mild symptoms were found on PD resistant cultivars. Two toxic compounds were also isolated from the XF culture filtrate. This result indicated that PD symptom development maybe associated in part with a toxic effect from X. fastidiosa. Our studies revealed that the PD development involves a series of complex interactions between the XF pathogen and the host plant, and many physiological and biochemical changes occured in the host plants during PD development.
• Publication Date: Aug 2003
• Journal: Hortscience