Xylella fastidiosa biology and ecology

Matt DaughertyDepartment of Entomology

UC Riverside

vector

pathogen host

Xylella vectors

Xylella host speciesor varietiesXylella

strains

Xylella fastidiosa: The early years

Anaheim vine disease

-1882

-30,000 - 40,000 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

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

First described in Southern California (1882)

Prevalent throughout California, except

-mountains-far North?

AZ, Gulf states, up to Virginia

Costa Rica

Brazil

Europe

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

1. Vessel occlusion -bacterial aggregates -restricted water flow -water stress symptoms

2. “Phytotoxin” -toxin not known

Mechanism of pathogenicity

-X. fastidiosa growth depends on temperature

Cold

Hot

- mean daily min/max: 17/24°C

-mean daily min/max: 21/36°C

Overwinter recovery from infection

-depends on timing of inoculation

-more recovery in colder climates?

100+ described plant species, from 30 plant families

-most do not host Xylella or show no symptoms

-some are susceptible

Wild/escaped grapeHimalayan blackberryPeriwinkleSpanish broomBlack mustard…

Host range

OleanderSweet gumOaksMapleElm…

GrapeAlfalfaAlmondPeachPlum

OlivePecanPearCoffeeCitrus

Crops WeedsOrnamentals/natives

-grape varieties exhibit a wide range of symptom severity

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

Management in Northern California vineyards

-vector resides in riparian corridor

-sweeps seasonally into vineyards

-management targets riparian hosts

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

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

Infection ≠ disease

-not all strains cause disease in other hosts

-even closely related strains may not be equivalently virulent

Variation in Xylella pathogenicity

Alm Gr

Ole Gr

Cit Cofx

x

healthy

grape strain

healthy

almond strain

Strain variability for alfalfa dwarf

-alfalfa is susceptible to both grape and almond strains

-grape strains are more virulent than almond

-grape isolates cause more severe water stress

-grape strains produce higher infection rates

Transmission depends on:

-host plant type

-X. fastidiosa strain

Determined by infection level

Pro

po

rtio

n t

ran

smit

tin

g

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

Disease management

Disease severity and reservoir status are affected by:

1.Host plant species or variety

2.X. fastidiosa strain

Disease management requires improved knowledge of “problematic” hosts and strain prevalence

http://www.cnr.berkeley.edu/xylella/

http://xylella.org

http://www.piercesdisease.org/

http://www.cdfa.ca.gov/pdcp/

http://cisr.ucr.edu/