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

vector host pathogen

Xylella vectors Xylella host species or varieties Xylella 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

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

-X. fastidiosa growth depends on temperature

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

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

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

-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

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

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

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

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

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

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

http://www.cnr.berkeley.edu/xylella/ http://xylella.org http://www.piercesdisease.org/ http://www.cdfa.ca.gov/pdcp/ http://cisr.ucr.edu/