Getting Solutions to PD from the Lab to Growers
By Peter Matlock, Technology Facilitator
C
W I N T E R
ontinued support of research on Pierce’s disease (PD) management technologies has provided an impressive
portfolio of potential candidates for commercialization. A wide range of management strategies is moving
forward, and this pipeline promises to deliver continuing product introductions over many years.
Closest to commercialization are PD-resistant winegrape varieties bred by Dr. Andy Walker, who uses a comprehensive breeding
program, including sophisticated molecular markers, to rapidly
backcross PD resistance from wild sources into vinifera background.
New cultivars with up to 97% vinifera background are in field trials
in PD hotspots in California, Texas, Alabama, and (soon) Florida.
Dr. Walker has arranged to make wines and wine blends from his
new cultivars, and held multiple tastings in Davis, Healdsburg,
Temecula and Napa. The wines are well-received, with frequent requests from growers for vines to
plant. Fifteen cultivars of 94%
and 97% vinifera background
(including Cabernet, Chardonnay, Zinfandel, Petite Sirah
and others) and three resistant
rootstocks were submitted to
Foundation Plant Services at UC Davis in early 2013, with another
round of advancements expected soon. The earliest release of these
cultivars to nurseries is expected in 2015, although commercial
availability of registered material is expected to take an additional
two to six years. In the meantime, investigations are under way
to expand field trials in California to demonstrate performance of
these cultivars under a broader range of commercial vineyard conditions.
b u l l e t i n
method), while another is to confuse the bacteria so they bind
together as if they were in a different part of their natural life cycle
(Dr. Steven Lindow’s work on diffusible signal factors);
• The “search and destroy” combination of proteins that seek out Xf,
bind to it and break up the bacteria (Dr. Abhaya Dandekar);
• The “life support” approach to keep grape plants alive even when
infected with Xf by preventing programmed cell death reactions
(Dr. David Gilchrist’s PR1 and
UT456); and
2 0 1 4
Research Breakthroughs Reported
During 2013 PD Research Symposium
The earliest release of these cultivars to nurseries is expected
in 2015, although commercial availability of registered
material is expected to take an additional two to six years.
As longer term insurance to provide additional protection against
PD, four different modes of action are currently in field trials and
in layman terms could be described as follows:
• “Gum ‘em up” approaches immobilize Xylella fastidiosa (Xf)
bacteria within one location and prevent their spread throughout
the plant. One approach is to bind the bacteria together using
a natural protein “glue,” (Dr. Bruce Kirkpatrick’s hemagglutinin
• The “take away the keys to
the car” approach to prevent Xf
movement from one xylem cell to
another by shutting down a bacterial
enzyme that would otherwise dissolve inter-cellular membranes
and allow such movement of the bacteria (PGIP: Drs. Ann Powell,
John Labavitch and Abhaya Dandekar).
New strategies continue to be explored in research laboratories, including potential bio-control sprays, beneficial bacteria that could
compete with Xf in the plant tissue, approaches to interfere with
insect transmission, and others.
Altogether, these strategies offer great promise with different technologies expected to become available over different time periods.
New cultivars from breeding programs can be expected first, with
other approaches offering potential over the coming decades.
To have learned so much about the underlying biology of a complex
problem like PD and to have developed multiple disease management
strategies, in such a short time, is a remarkable accomplishment.
INSIDE THIS ISSUE
PA G E 2
GWSS Eradicated
in SLO County
The GWSS are now gone. Read
about how the local community
worked together and the step by step
process it took to eradicate them.
PA G E 3
On the Research Front
• An evaluation of virulent phages
that attack Xylella fastidiosa
I
n December, some of the world’s leading pest control and viticulture experts
gathered in Sacramento to discuss the latest findings in the fight against Pierce’s
disease (PD) and the glassy-winged sharpshooter (GWSS).
Nearly 100 researchers, government officials, and winegrape growers attended the 2013 Pierce’s Disease
Research Symposium, organized by the California Department of Food & Agriculture’s PD Control Program. Presentations covered a broad array of issues during a packed two-day program. Topics ranged from
simple tweaks involving traditional pest control methods to complex techniques utilizing novel ways to
stop the disease. Special guest speakers also updated the group on successful policies and programs being
tested statewide, as well as emerging threats overseas.
“We’re halfway down the field
towards touchdown, and the next
step is critical. With a little bit of
funding and hard work, we can turn
our research into something practical.
I’d usually say don’t look a gift horse
in the mouth, but I’m sure looking,”
Dr. David Gilchrist, UC Davis.
During poster sessions, researchers were able to show just
how far their research has gone in recent years, highlighted by the many projects that are close to producing
actionable, commercially-appealing control methods.
“We’re halfway down the field towards touchdown, and
the next step is critical. With a little bit of funding and
hard work, we can turn our research into something
practical. I’d usually say don’t look a gift horse in the
mouth, but I’m sure looking,” said Dr. David Gilchrist, a
professor of plant pathology at UC Davis who has demonstrated a new technique to protect vines from PD.
Many strategies were discussed at the symposium and
some indicate that marketable solutions could be at
hand. For example, vintners statewide already have
had the opportunity to taste wines made from grapes
developed by Dr. Andy Walker of UC Davis, a researcher funded by the PD/GWSS Board who has bred
PD-resistant Vitis vinifera vines.
Continued on page 2
• Blocking Xylella fastidiosa
transmission in grapevines
• Report on the continued field
evaluation of diffusible signal
factor (DSF) producing grapes to
control PD
PA G E 4
Getting Solutions to PD
from the Lab to Growers
A look at some of the possible
solutions to PD and what needs to
happen to get them out of the lab
and into vineyards.
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By Marc A. Lea, Deputy Agricultural Commissioner, San Luis Obispo County Dept. of Ag
San Luis Obispo County sits between Santa Barbara and Monterey counties along California’s Central Coast, with
Kern County and the Central Valley directly to the east. Considering the statewide distribution of the glassy-winged
sharpshooter (GWSS), where southern counties are either generally or partially infested and most of Northern California is uninfested, San Luis Obispo County serves as an important buffer area.
In September 2010, three nymphs and an adult GWSS were
detected in a single-panel trap. The trap had been placed in a citrus
tree located in a southeast San Luis Obispo residential neighborhood. Due to the multiple life stages detected, the original find
constituted a breeding population, the county’s first. After an
exhaustive series of visual surveys and increased detection trapping
by the San Luis Obispo County Department of Agriculture, four
additional adult GWSS were found along with three viable egg
masses and numerous old egg masses.
The neighborhood
in question is located
directly north of the
Edna Valley Appellation, sitting less than
a mile away from
a growing area of
approximately 2,000
acres well renowned
for producing high
quality Chardonnay
and Pinot Noir. Additionally, winegrapes are extremely
important to the
county’s overall
economy, with nearly
40,000 acres in
production, and generally are among the
highest valued crops
in the county.
A contractor injects imidacloprid into the soil in the
backyard of a home in the infested area.
After extensive
research, county
officials decided to delay insecticide applications until early spring.
The success of the project hinged on garnering the support of the
local neighborhood, and the Department was hesitant to rush into
making applications in a suburban neighborhood, a situation un-
Research
Front
on the
The Eradication of GWSS in SLO County
precedented in the county and one likely to cause concern among
residents.
During the intervening months, the Department of Agriculture
conducted a great deal of public outreach both to the affected
residents and other groups in SLO County with general concerns
about the project. A contractor was hired and a detailed protocol
for the applications was developed - a protocol that included obtaining permission from each resident whose property was targeted
for treatment, notifying adjacent property owners of upcoming
treatments and hosting a public informational meeting open to any
concerned residents.
During the intervening months, the Department of Agriculture conducted
a great deal of public outreach both to the affected residents and other
groups in SLO County with general concerns about the project.
Virulent Phages of Xylella fastidiosa: Prophylactic
and Therapeutic Evaluation
Principal Investigators: Carlos F. Gonzalez and Ry Young
Dept. Plant Pathol. & Microbiol., Texas A&M University, College Station, Texas
Bacteriophages (phages) are viruses that attack bacteria and do so without posing any harmful effects to
their hosts. Researchers have isolated and propagated the first virulent phages for Xylella fastidiosa (Xf )
and have illustrated possible usage in the treatment of Pierce’s disease. Four Xf phages were chosen for
this study. Lab tests showed that all four phages were virulent and proved effective during greenhouse
experiments. An ongoing trial will test efficacy under field conditions. Application of phages as biocontrol
agents for Xf offers a novel biological treatment for control of Pierce’s disease.
An electron micrograph of
a bacteriophage (phage)
attacking a bacteria cell.
Soil applications commenced in February 2011, and CoreTect
tablets (containing imidacloprid) were placed in the soil beneath
citrus trees. Citrus trees are common within this neighborhood,
and since they are also a preferred GWSS host, it was important
that the citrus was effectively treated.
Blocking Xylella fastidiosa Transmission
Principal Investigator: Rodrigo Almeida
Dept. Environmental Science, Policy & Mgmt., UC Berkeley, Calif.
Several wasp species of egg parasitoids were released within the area
and focused on untreated areas along the perimeter of the infestation, and a few properties in which the residents requested that
insecticides not be used.
In all, 114 residential properties were treated during 2011, with
over 90% of the property owners approving insecticide applications at their residence during February and March, with a small
“bump-out” area being treated in August after an additional
GWSS detection. No additional GWSS were detected after treatments ended in August 2011.
After two more years of extensive trapping and annual visual surveys with no additional detections, the California Department of
Agriculture declared the area eradicated in December 2013.
Research Breakthroughs Reported during 2013 PD Research Symposium - continued from page 1
Dr. Carlos Gonzalez, a researcher at Texas A&M University, found success with a virulent cocktail of bacteriophages, viruses that infect
bacteria. These phages could be used as a vaccine to prevent or treat Pierce’s disease in grapevines.
Other presenters discussed San Luis Obispo County’s successful GWSS eradication efforts, new PD-related plant disease outbreaks in
Europe and the multi-million dollar economic benefits of PD research on California agriculture. An evening poster session allowed
researchers and other attendees to discuss research projects and advances in an informal, one-on-one setting.
As in prior years, the symposium provided a forum for PD researchers to meet and exchange ideas, encouraging scientific collaboration
and accelerating progress towards finding solutions to the disease. A compendium of research progress report produced in conjunction
with the symposium is available online at http://www.cdfa.ca.gov/pdcp/Documents/Proceedings/2013_Proc.pdf. Printed copies are also
available and can be requested by calling the Pierce’s Disease Control Program at 916-900-5024.
PA G E 2
Cage on grapevine holding bluegreen sharpshooters during inoculation of Xf on a grapevine.
This research found that a previously identified enzyme in Xf is required for effective colonization
in both insect and plant hosts. The finding that this enzyme is important for both life stages of Xf
provides the opportunity to develop control strategies that could affect both disease development in
plants and vector transmission between plants. In addition, it was found that Xf proteins associated
with vector colonization block Xf transmission to plants. Research also found two proteins that reduce
Xf transmission to plants under greenhouse conditions. This work has resulted in findings that impact
our understanding of Xf colonization of plants and insect vectors. It also identified peptides that outcompete Xf for binding sites in its vector, effectively blocking transmission.
Continued Field Evaluation of Grapevines Producing
Diffusible Signal Factor for Control of PD
Principal Investigator: Steven Lindow
Dept. of Plant & Microbial Biology, UC Berkeley, Calif.
Xf can be suppressed by the introduction of a diffusible signal factor molecule (DSF) which acts to
suppress PD symptoms in grape vines. Modified Freedom grapevines used in field trials in both Solano and Riverside counties remain more highly resistant to Pierce disease than the unmodified plants.
In Thompson Seedless grapes, the modified scion were similar in susceptibility to the unmodified
grapevines, but the modified vines displayed substantial disease control when used as rootstocks.
The work demonstrates that in two different grape varieties the severity of PD can be reduced by the
production of DSF in plants. The results are quite promising and provide substantial evidence that
this strategy will be effective in reducing the severity of Pierce disease in a wide variety of grapevines.
PA G E 3
Healthy modified Freedom grapevines
at the Riverside field trial show promising results in their resistance to Xf.