Page 36 - Grapevine May-June 2020

Around The Vineyard

develop dual resistance to leafroll and mealybugs tem. Initial experiments to introduce Pf PsJN were
by modifying the genome of grapevine varieties done by prickling the leaves of the vine, however,
using a gene silencing technology known as RNAi. this would not be practical in a commercial set-
Using genetic engineering it is possible to introduce ting. So far, experiments using a surfactant to help
portions of DNA that specifically will degrade the the bacteria penetrate the grapevine’s conductive
nucleic acid of the infecting virus and the mealybug tissue (xylem) have been successful. The work is
able to transmit it. This method is being successful- in progress and has shown that Pf PsJN is capable
ly used in Hawaii to control Papaya ringspot (PRSV), of inhibiting Xf disease development even after Xf
a virus that had decimated the papaya production infection had started. Research will continue and
in the islands. Thanks to this technology, Hawaii is is focused on determining the timing of application
able to produce healthy papayas that resist PRSV. that would offer the best disease protection. It
Simply described, the plant genome would be able is expected that once developed, the product will
to detect viral and/or insect nucleic acids and chop need to be tested and registered with the EPA as
them up before they are able to sequester the biological pesticide before its commercialization
plant’s metabolic machinery to their advantage and and/or use in the field.
cause disease.
Use of UVc Light (Germicidal Lamps)
Biological Control of to Control Powdery Mildew
Xylella fastidiosa the Causal Agent of
Pierce’s Disease in Grapevines Dr. Michelle Moyer described the powdery mildew
disease agent as a “Goldilocks fungi”, as conditions
Steve Lindow presented the research focused on must be “just right” for infections to occur. The
the use of an endophytic bacteria capable of reduc- temperatures must not be too cold, and not too
ing the incidence of Xylella fastidiosa (Xf) in grape- hot. The humidity cannot be too high or too low.
vines. Pierce’s Disease (PD) is a devastating disease It is well known that controlling powdery mildew
and in the past years an increase in the infection in the vineyard is probably the largest pest control
rates of the bacteria has been seen in California item line in the budget. We all know that there
vineyards. It is not clear what is the reason for the are management practices that can be applied to
sudden increase of disease incidence. It is theo- reduce the incidence of powdery mildew such as
rized that the increased infections could be due leaf thinning, opening the canopy to favor air flow
to the ability of other insects (cicadas, spittlebugs) and light but these are not sufficient to avoid the
to transmit the bacteria or perhaps due to climate multiple powdery mildew season’s infections in a
change (less severe winters in California). vineyard.

In a project funded by the PD Board, Professor
Lindow’s group has discovered an endophytic bac-
terial species that appears to inhibit Xf propagation
in grapevine and acts as a biological control agent.
An endophyte is an organism capable of living and
multiplying in its host (in this case grapevines)
without causing disease. The endophytic bacteria
is Paraburkholderia phytofirmans strain PsJN (Pf
PsJN). As described at the presentation, the endo-
phytic Pf PsJN acts as a vaccine activating the dis-
ease resistance pathways in the colonized plants.
The endophytic Pf PsJN can multiply rapidly in the
colonized grapevines without causing disease.

Furthermore, Pf PsJN is able to reduce the pop-
ulation of Xf and avoid disease development in
experimental vines. The challenge presented in the
application of this biological control agent (as well A vineyard with high powdery mildew
as others) is to develop an appropriate delivery sys- disease pressure.

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