EMBARGOED UNTIL: Tuesday 5/21, 1 PM MDT

(Poster Session 205, Paper 2434)

Jiue-in Yang
University of California, Riverside
Moreno Valley, CA, United States
Phone: 951-315-8167
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The objective of this study is to identify beneficial living organisms (a.k.a. biocontrol agents) inhabiting grapevine that can inhibit Xylella fastidiosa (Xf), the causal agent of Pierce’s Disease (PD). Xf poses a severe threat to several major California crops including grapes, almond and citrus. Xf is a bacterium that lives in the water conducting tissue of the plant, multiplies to a high number and eventually blocks the water flow, which causes the plant to die as little as two years. Xf is vectored by insects and is transmitted as insects feed on the plant. The recent introduction into California of a more effective insect vector led to a PD epidemic with severe economic consequences. PD has already impacted 25 percent of Temecula Valley's vineyard in Riverside County, resulting in an estimated $13 million in damage in that county alone. The potential for the introduced insect vector to move to northern California threatens the $3.8 billion grape industry as well as other agricultural commodities. Current management strategies for PD rely mostly on insect vector control with insecticides. There are no effective control measures in place that effectively cure the plant of the bacterium itself. Our team is exploring the use of natural biocontrol agents inhabiting grapevine and the anti-Xf molecules that they produce as novel control strategies for PD. If successful, this work will change the current management practice of this important disease, and will reduce pesticide input in the environment and its associated negative impact on human health and natural resources. 

This work is currently funded by the ‘California Department of Food and Agriculture / Pierce’s Disease and Glassy Winged Sharpshooter Research Board. Drs. Rolshausen and Yang at the University of California Riverside (UCR) in the Botany and Plant Sciences Department are identifying the biocontrol agents for Xf. Drs. Roper and Borneman, Department of Plant Pathology and Microbiology at UCR, provide guidance with the interpretation of the results as well as technical and logistic support. Dr. Mahoney, from the Chemistry Department at Point Loma Nazarene University, and Dr. Gloer, from the Chemistry Department at the University of Iowa, are identifying the antibiotics produced by the biocontrol agents that are inhibitory to Xf. The work is being presented at the annual ‘American Society for Microbiology’ conference in Denver on June 21st 2013.

In this study, we aim to characterize the microbial population profiles of vines that are symptomatic (diseased) in comparison to those that do not express symptoms while growing under high disease pressure (escaped), in order to identify potential biocontrol agents of Xf. We hypothesized that some grapevines are capable of escaping PD because of the microbial communities residing in the vines and not because of the plant genetics given that the vines are clonal. We selected vineyards under high PD pressure in Riverside and Napa counties, California, and collected sap, shoot, and petiole samples. Microorganisms inhabiting escaped and diseased grapevines were identified in two ways. First, fungi were cultured on fungal medium and identified based on DNA sequences. Second, a culture-independent DNA-based method was applied in order to obtain the complete microbial profile of these plants (including the microorganisms that did not grow under the culture conditions used). Our results showed that diseased and escaped vines contained both similar fungal groups and unique specimens. Seven fungi recovered from vines inhibited the growth of Xf in laboratory tests. Natural compounds secreted by these antagonistic fungi were extracted and two of the purified natural molecules present showed inhibition of Xf growth in laboratory tests. Both biocontrol agents and compounds are currently being evaluated for control of PD in planta in greenhouse assays. If successful, these biocontrol agents and/or compounds could be used for the management of PD in grapevine but could also be considered as possible treatments for diseases caused by Xf in other crops such as citrus and almond. In addition, this work will open new research avenue for the management of other diseases in other cropping systems.