1. Xylella fastidiosa biology and ecology
Matt Daugherty
Department of Entomology
UC Riverside

2. vector
host
pathogen

3. Xylella vectors
Xylella
host species
or varieties
Xylella strains

4. Xylella fastidiosa: The early years
Anaheim vine disease
-1882
-30, ,000 acres lost
-50 wineries closed
Pierce investigated viticulture, climate,
epidemiology
Vector and pathogen not known
-thought to be a virus
Isolated, identified as bacterium in 1978
Newton B.
Pierce

5. Xylella fastidiosa biology
Xylem-limited bacterium
Wide host range
-crops, native, ornamental, weedy plants
-disease severity differs among hosts
Substantial genetic variation
-host-specific strains
-pathogenicity varies among strains
Transmitted by xylem-sap feeders
-sharpshooters are most important vectors
-many sources of variation
No cure

6. First described in Southern California (1882)
Prevalent throughout California, except
-mountains
-far North?
AZ, Gulf states, up to Virginia
Costa Rica
Brazil
Europe

7. Xylella fastidiosa transmission
No latent period
Nymphs & adults can transmit
-no transmission after molting
-persistent in adults
Species differ in efficiency
Efficiency tied to plant infection level
> 10,000 cells/g plant

8. Mechanism of pathogenicity
1. Vessel occlusion
-bacterial aggregates
-restricted water flow
-water stress symptoms
2. “Phytotoxin”
-toxin not known

9. -X. fastidiosa growth depends on temperature

10. Cold
mean daily min/max:
17/24°C
-mean daily min/max:
21/36°C
Hot

11. Overwinter recovery from infection
-depends on timing of inoculation
-more recovery in colder climates?

12. Host range 100+ described plant species, from 30 plant families
-most do not host Xylella or show no symptoms
-some are susceptible
Crops
Grape
Alfalfa
Almond
Peach
Plum
Olive
Pecan
Pear
Coffee
Citrus
Oleander
Sweet gum
Oaks
Maple
Elm …
Ornamentals
/natives
Wild/escaped grape
Himalayan
blackberry
Periwinkle
Spanish broom
Black mustard …
Weeds

15. -grape varieties exhibit a wide range of symptom severity

16. Identifying X. fastidiosa reservoirs
1. preferred feeding hosts of
vectors?
2. high infection levels?
3. systemic infection?
Not known for most landscape and nursery plants

17. Management in Northern California vineyards
-vector resides in riparian corridor
-sweeps seasonally into vineyards
-management targets riparian hosts

18. Control is achieved by targeted removal of key hosts for pathogen/vector

19. Xylella fastidiosa genetic variation
Host-plant associated pathogen
strains
3+ groupings in the U.S.
-grape, almond
-almond, oak, peach, plum
-oleander
Strains are biologically distinct

20. Variation in Xylella pathogenicity
Alm Gr
Infection ≠ disease
-not all strains cause disease in other hosts
-even closely related strains may not be equivalently virulent x
Ole Gr x
Cit
Cof

21. Strain variability for alfalfa dwarf
healthy
Strain variability for alfalfa dwarf
-alfalfa is susceptible to both grape and almond strains
-grape strains are more virulent than almond
grape strain
healthy
almond strain

22. -grape strains produce higher infection rates
-grape isolates cause more severe water stress

23. Proportion transmitting
Transmission depends on:
-host plant type
-X. fastidiosa strain
Determined by infection level
Proportion transmitting

24. Disease management Landscape management -remove alternative hosts
-remove diseased vines (roguing)
Develop resistant host varieties
-back-crossing with resistant varieties
-GMO approach (DSF, or PGIP mutants)
Avirulent/symbiotic strains
-outcompete X. fastidiosa

25. Disease severity and reservoir status are affected by:
Host plant species or variety
X. fastidiosa strain
Disease management requires improved knowledge of “problematic” hosts and strain prevalence