Research and IPM

Grants Programs: Pierce's Disease Research

2008-09 RFP Attachment A
Research priorities

(from: PD/GWSS Research Scientific Review, Final Report, August 2007, Research Scientific Advisory Panel)

Research proposals that address the following key research areas will be given funding priority by the CDFA program.  Proposals in other areas will not be rejected a priori. However, all proposals must include an explanation of how the proposed research can lead to reductions in the PD problem and development of a sustainable PD management strategy. Both the CDFA and UC programs will take into account the perceived applicability of the anticipated results when making awards.

Biological Research Priorities

Exploiting Xylella fastidiosa (Xf) virulence factors to control Pierce’s disease.  In the last four years, several labs have participated in the effort to knock out Xf virulence genes and/or overexpress them, followed by testing the mutant strains for virulence on grape.  This work has led to several important insights that can potentially be applied to new PD control strategies.  Various transgenic and non-transgenic strategies can be envisioned for interfering with the function of protein-based factors, and thus conferring resistance to Xf infection; however, most research projects have not yet advanced to the point of demonstrating such a control method.

Priority areas include:

• Use of Diffusible signal factor (Dsf) for disrupting Xf colonization, including delivery by plant associated microbes, transgenic rootstocks, and application of chemical analogs.
• Inhibition of Xf polygalacturonase (PG).  This research area includes identification of PGIPs with high activity against Xf PG, delivery of PGIP to grape plant scions from transgenic rootstocks, and development of small molecule inhibitors of Xf PG.
• Targeting other Xf proteins required for virulence.  This research area includes development of protein/peptide-based inhibitors of cell surface proteins such as pilins and adhesins, along with identification of chemical inhibitors of these proteins.

Biological control of GWSS using parasitoids.  The use of parasitoids to reduce population densities of GWSS continues to show promise, especially in settings where synthetic insecticidal sprays cannot be used (e.g. organic farms, urban areas, or other non crop habitat).  The labor-intensive methods required to produce parasitoids are currently a major limitation of this approach.

Priority areas include:

• Production of parasitoids, with a particular emphasis on developing efficient means of mass producing GWSS eggs or an alternative suitable host for large-scale production of parasitoids.
• The utility of natural enemies (with an emphasis on native and introduced parasitoids) to suppress PD should be measured, particularly with respect to impact on GWSS populations in the field and under diverse environmental conditions (cultural practices and climatic differences).  Further work should be conducted to quantify the value of natural enemies as an integral component of PD disease control programs in urban and rural communities.  Further, limited research on conservation of existing parasitoids is warranted (e.g. by understory plantings that provide key resources, nectaries, over-wintering sites, etc.). The evaluation of new, imported species of parasitoids should focus on realistic assessments of their potential for greater impacts on PD than from currently established natural enemies (such as with the aid of models). Potential agents hypothesized to be more effective early in the season and suited to the California climate should be a priority.  The potential impact of imported parasitoids on native non-pest leafhoppers should be assessed before release is allowed, using realistic host specificity trials.

The role of Xf genotype in vector and plant transmission and virulence.  There is a need for better understanding of the distribution, abundance, and movement of strains of Xf in agricultural and nonagricultural settings.

Priority areas include:

• Development and deployment of efficient Xf genotyping tools for monitoring Xf presence in GWSS populations, non crop plants, and crops.  Studies involving Xf genotyping are necessary at the local population as well as regional level.
• Integration of Xf genotype data into the CDFA GIS database.
• Epidemiological analyses of Pierce’s disease outbreaks in relationship to presence of specific Xf genotypes and their abundance in adjacent crop and non-crop plants, and GWSS populations.

Host resistance to Pierce’s disease.  In annual crop species, the most cost effective and environmentally safe method for preventing disease is breeding for resistance. Such traditional breeding can be dramatically accelerated if the genes controlling resistance have been linked with DNA-based molecular markers that can be scored in a high throughput fashion. A second area that merits more attention in the short-term is collection and dissemination of information on PD resistance in existing commercial varieties of grapes.  There appears to be significant anecdotal information about which commercial grape varieties are most susceptible to PD, but it does not appear that any one has performed a carefully controlled study of commercial grape varieties and disseminated the results.

Priority areas include:

• Marker Assisted Selection-based breeding for resistance. The RSAP recommends recruitment of additional breeders so that genes in addition to PdR1 can be mapped, tagged with molecular markers, and the process of introgression into multiple commercial backgrounds initiated.
• Assessment of PD resistance in existing commercial grape varieties.  The RSAP envisions greenhouse studies employing both GWSS-mediated inoculations in one set of experiments and mechanical inoculations in another set, to distinguish between resistance derived from reduced attractiveness to the vector versus reduced susceptibility to colonization by the bacterium.  Data on both PD symptoms and Xf growth should be obtained to distinguish also between tolerance and resistance, as tolerant varieties could become problematic reservoirs of the pathogen.

Economic Research Priorities

Economic analysis of the impact of PD/GWSS on agriculture, both in terms of real and potential economic effects and economic losses due to PD and the effects of current and prospective control measures, including losses to growers and other market participants.

These specific topics are illustrative and are not listed in priority order:

• Modeling and measuring the economic effects of the current PD/GWSS disease situation.  How has PD/GWSS affected costs, acreages, prices and quantities?  How much cost has been incurred so far and who has incurred those costs among consumers, producers, taxpayers, and other stakeholders by crop?
• What are the economic lessons from diseases other than PD/GWSS in terms of economic impacts of the diseases themselves and economic lessons about control approaches and policies?
• What are the impacts on disease control and economic effects of alternative government and industry-wide policies for dealing with PD/GWSS?  What policies complement alternative research and development strategies? 
• Simulating alternative ex ante scenarios of the economic effects if PD/GWSS were to continue unabated.  What are the likely impacts on costs, acreages, prices and quantities?  How much cost is likely to be incurred, who is likely to incur those costs among consumers, producers, taxpayers, and other stakeholders by crop?
• Evaluate, in an ex ante sense using simulation models, the likely contributions of alternative investments in PD/GWSS research and development.  Such a project could evaluate the potential contributions of several alternative R&D efforts that have different impacts on control of PD/GWSS and different time horizons.  Such a project would not attempt to evaluate the likely scientific merit of alternative research efforts, but rather assess the payoff for the industry, including consumers, if reasonable success is obtained.

Supplemental Page for All Biological Research Proposals

Selection of Pierce’s disease control objective(s): Fig. 1 above summarizes the events in the Xylella fastidiosa infection cascade leading to the development of Pierce’s disease of grapevine. A viticulture tool or practice or other control measure that can interrupt or prevent any of these events presumably has the potential to contribute to the goal of controlling Pierce’s disease.

Each applicant submitting a Biological Research Proposal is requested to indicate the relevance of the proposed research by identifying one (preferably) or up to three events diagrammed in Fig. 1 as the direct or indirect target(s) against which anticipated research results are directed. Identify the most relevant event by marking the corresponding box with the number 1. If the anticipated research results are expected to affect significantly one or two other events, mark other boxes accordingly with “2” or “2” and “3.” Some proposed projects may not be targeted even indirectly to a specific event in the infection course but rather may be aimed at developing technology that will assist generally in meeting the goal of Pierce’s disease control, i.e., an enabling technology (box J). To assist the applicant in defining the area of his or her proposal, examples, which are intended only as examples, are given below.

• A project is aimed at developing more effective methods for killing sharpshooters or identifying and eliminating Xf source plants – mark “1” in box A.
• A Xf-colonizing bacterial strain is to be developed that competes with Xf and prevents Xf acquisition by the sharpshooter – mark “1” in box B.
• A project is aimed at developing a grapevine line that produces a sharpshooter repellent; mark “1” in box C.
• A project is aimed at developing a bacterial spore that is to be sprayed on grapevines to infect sharpshooters and greatly reduce their ability to continue spread of Xf – mark “1” in box D.
• A chemical spray is to be developed that interferes with the ability of sharpshooter-delivered Xf to form colonies in the xylem – mark “1” in box E.
• A transgenic grapevine is to be created in which Xf is to be confined by a biofilm-binding protein to the initially colonized vascular element – mark “1” in box F.
• A low molecular weight inhibitor of a Xf enzyme is to be synthesized in grapevine by alteration of a secondary metabolite pathway, resulting in confinement of Xf to the initially infected xylem element – mark “1” in box G.
• A chemical spray is to be developed that will counteract the effects of a Xf toxin that contributes to development of Pierce’s disease symptoms – mark “1” in box H.
• A drench is to be developed that will result in root uptake and systemic spread of an antibiotic that kills Xf cells – mark “1,” “2,” and “3” in boxes E, F and G.
• A transgene system is to be developed for expression of proteins in grapevine rootstock that are efficiently delivered to the xylem and transported into the scion – mark “1” in box J, “2” in box E and “3” in box F.

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