Host List of Pierce's Disease Strains of Xylella fastidiosa

This is a list of plants in which Pierce's disease (PD) strains of Xylella fastidiosacan multiply. Hosts of other strains of Xylella fastidiosa (abbreviated as Xf) follow the PD list. The lists are alphabetically ordered by the scientific (Latin) name. We used the scientific and common names that appeared in the original references, with limited attempts to reconcile older names with more contemporary ones.

What does a plant's rating as a "host of Xylella" mean?

This list includes plants from which Xylellahas been recovered using a variety of detection methods. The plants posing the greatest risk in the development of Pierce's disease are those that·

Develop high populations of Xylella

Allow systemic movement of Xylella

Are preferred feeding hosts of important vector species
 
 

 What determined if a particular plant was tested?

Most of the plant species were selected because they are preferred by important insect vectors or because they commonly occur in habitats where those insects live. Not all possible host plants have been tested. The plants that insect vectors feed on most frequently are probably the most important reservoirs of Xf. Most of this research has been done in California using plants from areas that have had ongoing problems with Pierce's disease. Some plants were selected arbitrarily or because investigators were curious about plants that belonged to certain botanical families.

Why are there so many hosts?

PD strains of Xf can multiply to some degree within the great majority of plants that are inoculated with the bacterium. However, relatively few plants support moderate to high bacterial populations, and fewer still allow movement of Xf beyond the inoculation point. It is easier for an insect vector to pick up Xylellafrom plants that have high bacterial populations. Plants ranked "high" can support between 10 million and 1 billion live bacteria per each gram of tissue. "Low" category plants support less than 100,000 live bacteria per gram of plant. Vector acquisition of Xffrom plants in the "low" category is very inefficient. The ability of Xylellato move systemically throughout the plant, beyond the inoculation (insect feeding) point, is an important host attribute. Systemic movement enables the bacteria to spread on its own to a much larger volume of plant tissue, making it easier for feeding insects to pick it up.

What factors influence the growth of Xylellain a plant?

The growth of Xylella in plants depends on the bacterial strain (genetic variation), the plant's physiology and the temperature. Other factors not yet understood may also influence the fate of Xylella. The methods used to study Xf in plants also determine how well we observe what really happens to the bacteria. Each detection method reveals different kinds of information and has its own level of sensitivity and reliability.

Key to List Categories

** Plants which were tested and came out negative are indicated by asterisks**.

A blank cell indicates the data was not available.

FIELD ISOLATED: Xylellawas isolated from field-collected material after mechanical (needle) inoculation

GH ISOLATED: Xylellawas isolated from greenhouse-grown material after vector inoculation or needle inoculation. Greenhouse conditions can result in populations of bacteria that are several times higher than for the same plant species in the field.

POPULATIONS of Xf are expressed as:

High = 10 million to one billion live cells per gram of plant material

Medium = 100,000 to 9 million live cells per gram of plant material

Low = less than 100,000 live cells per gram of plant material

SYSTEMIC: "Y" means Xfwas recovered from tissues beyond the inoculation point. "N" means that the bacteria was not recovered. The bacteria moves from cell to cell in the xylem of the plant. A question mark (?) indicates that Xfwas detected at a long distance from the inoculation site but this may have been due to the xylem vessels in the plant being very long.

XfISOLATION TECHNIQUE: The method used to detect Xylellafrom plant material.

Vector = Infective insects were caged on plants, removed, and non-infective insects were placed on the same plants for varying intervals of days to weeks. The new insects were then moved to healthy grape or alfalfa test plants. If the test plants became diseased (PD in grapes, alfalfa dwarf in alfalfa), the original plant exposed to infective vectors was presumed to harbor the "virus." These experiments were done by Julius Freitag in the 1940s, when the cause of PD was assumed to be a virus.

Culture = Assays based on the growth of Xffrom finely ground plant samples plated onto semi-selective microbiological media and incubated. The number of live bacteria in the sample can be determined from the number of colonies that grow on the plate. The advantages of culture-based assays are that they quantitatively detect live cells, are fairly sensitive (down to thousands of Xfper gram) and highly reliable if the cultured bacteria are further confirmed as Xfby other means. Disadvantages are that the method requires at least a week to complete, other bacteria and fungi in plant samples can completely obscure the results, and certain plants (black walnut and coffeeberry, for example) contain substances which inhibit growth of Xfon the Petri dish.

ELISA = Enzyme-Linked ImmunoSorbent Assay uses antibodies against Xylellato detect if Xfoccurs in the sample. The antibodies bind specifically to proteins on the outer wall of Xf, and other reactions allow enzymes to cause a color change in proportion to how many antibodies are bound to Xf cells in the sample.  The more intense the resultant color, the more bacteria are present. Advantages of ELISA are it can indicate the quantities of Xf(dead or alive) in the sample and the test is easily run for many samples. Disadvantages are its low sensitivity (lower detection limit 100,000 Xfper sample), failure to distinguish live from dead Xfcells, and occasional false positive readings, especially for plants other than grape.

DIF = Direct ImmunoFluorescence uses antibodies against Xylellato bind a fluorescent indicator dye to Xfcells so they can be seen using a microscope that has ultravolet light illumination.

PCR = Polymerase Chain Reaction amplifies a Xylella-specific piece of DNA millions of times. The amplified DNA is visible as bands on a gel after separation in an electric field. PCR is becoming more widely used to detect Xf.It has the advantage that it is the most sensitive method for detecting Xf(to below 100 cells per sample), and can be used even for frozen or preserved samples. PCR also is unlikely to give false positives or be affected by the presence of other microorganisms. PCR can also be used to quickly distinguish some strains of Xf. Disadvantages are that it is generally not quantitative, it is still not widely available in diagnostic labs, and cannot distinguish DNA from living vs. dead bacteria. Some naturally-occurring chemicals in plants can inhibit PCR, resulting in negative test results even though Xfis present in the plant.

Budding = Xylellawas transmitted when budwood from an infected plant was grafted onto a previously healthy plant. This older method depends on accurate identification of the disease in the indicator (recipient) plants. Successful grafting requires the inclusion of live xylem ("wood") with the scion grafted onto the indicator plant.

 VECTOR HOSTS: Indicates which important sharpshooter species (for California viticulture) feed or lay eggs on the plant. Blanks indicate no data available or that the plant is not a host.

                          BGSS = Blue-Green Sharpshooter (Graphocephala atropunctata). See a list of preferred hosts in coastal California at:

http://www.CNR.Berkeley.EDU/xylella/control_guidelines.html
GSS = Green Sharpshooter (Draeculacepahala minerva). Primarily found in central California on pasture grasses, and wet locations on sedges and reeds. Highly prefers water grass and Bermuda grass in weedy situations.

GWSS = Glassy-Winged Sharpshooter (Homalodisca coagulata). See a list of preferred hosts at the California Department of Food and Agriculture's web site on GWSS at http://plant.cdfa.ca.gov/gwss/.

RHSS = Red-Headed Sharpshooter (Carneocephala fulgida). Primarily found in central California on pasture grasses, some sedges and reeds in wet spots. Highly prefers water grass and Bermuda grass in weedy situations.
 

 REFERENCES: Reference reporting the results for that host species. See the annotated list of references following the tables.

Plant Host Status for Pierce's Disease Strains of Xylella fastidiosa
 
Scientific Name Common Name
Field Isolated
GH Isolated
Systemic
Technique
Vector Host
 Reference
Acacia longifolia golden wattle
Y
vector
 Freitag '51
Acer macrophyllum big leaf maple 
Y (medium)
Y (medium)
Y?
culture
 P + S '99
Acer negundo box elder 
Y (low-med)
culture
 P + S '99
Aesculus californica California buckeye 
Y (medium)
Y (low)
culture
 P + S '99
Aesculus californica California buckeye
N
vector
 Freitag '51
Aesculus californica* California buckeye*
N
ELISA
 Raju, 1983
Agropyron sp.* crested wheatgrass*
N
ELISA
 Raju, 1983
Alnus rhombifolia white alder 
N
Y (low)
N
culture
 P + S '99
Ampelopsis arborea peppervine
Y
ELISA/cult./DIF
 Hopkins '88
Amsinckia douglasiana buckthorn weed 
Y
vector
 Freitag '51
Artemisia absinthium* mugwort*
N
ELISA
BGSS
 Raju, 1983
Artemisia douglasiana mugwort
Y (low-med)
culture
BGSS
 P + S '99
Artemisia douglasiana mugwort
Y
Y
vector
BGSS
 Freitag '51
Artemisia douglasiana mugwort
Y (medium)
N
ELISA/culture
BGSS
 H + P '95
Avena fatua wild oat
Y
vectors
 Freitag '51
Avena fatua wild oat 
Y
vectors
 Freitag '51
Baccharis pilularis coyote brush 
N
Y (low-med)
N
culture
 P + S '99
Baccharis pilularis coyote brush
Y
vectors
 Freitag '51
Baccharis salicifolia mule fat
Y (medium)
N
culture
BGSS/GWSS
 P + S '99
Beta vulgaris* sugar beet*
N
vectors
 Freitag '51
Bidens pilosa var. pilosa beggar-ticks
N
vectors
 Freitag '51
Brassica rapa* field mustard*
N
vectors
 Freitag '51
Bromus catharticus rescue grass
Y
vectors
 Freitag '51
Bromus rigidus ripgut grass
Y
Y
vectors
 Freitag '51
Bromus sp. Russian brome grass
Y
vectors
 Freitag '51
Callicarpa americana American beautyberry
Y
ELISA/culture
 Hopkins '88
Callistephus chinensis China aster
Y
vectors
 Freitag '51
Calycanthus occidentalis* spicebush*
N
culture
 P + S '99
Calycanthus occidentalis* spicebush*
N
vectors
 Freitag '51
Canna sp. Canna
Y
vectors
 Freitag '51
Chenopodium ambrosioides Mexican tea
N
culture
BGSS
 P + S '99
Chenopodium ambrosioides Mexican tea
Y
Y
vectors
BGSS
 Freitag '51
Citrus limon lemon 'Meyer' 
N
vectors
GWSS
 Freitag '51
Citrus reticulata tangerine
N
vectors
GWSS
 Freitag '51
Citrus sinensis sweet orange
Y (low)
culture
 Hopkins Î91b
Claytonia perfoliata miner's lettuce
Y
ELISA
 Raju, 1983
Conium maculatum poison hemlock
Y
culture
 P + S '99
Coprosma baueri Coprosma
Y
vectors
 Freitag '51
Cotoneaster francheti Cotoneaster
N
vectors
 Freitag '51
Cotoneaster rotundifolia cotoneaster
Y
vectors
 Freitag '51
Cynodon dactylon Bermuda grass
Y
Y
vectors
RHSS/GSS
 Freitag '51
Cynodon dactylon Bermuda grass*
N
ELISA/culture
RHSS/GSS
 H + P '95
Cynodon dactylon* Bermuda grass*
N
ELISA
RHSS/GSS
 Raju, 1983
Cyperus acuminatus* sedge*
N
culture
RHSS/GSS
 P + S '99
Cyperus eragrostis purple nutsedge
Y
culture
RHSS/GSS
 P + S '99
Cyperus esculentus yellow nutsedge
Y
vectors
 Freitag '51
Cytisus scoparius Scotch broom
Y
Y (med-high)
vectors
 Freitag '51
Daucus carota var. sativa short white carrot 
Y
vectors
 Freitag '51
Daucus carota* wild carrot*
N
ELISA
 Raju, 1983
Digitaria sanguinalis hairy crabgrass
Y
vectors
 Freitag '51
Digitaria sanguinalis hairy crabgrass
Y
vectors
 Freitag '51
Distichlis spicata* saltgrass*
N
vectors
 Freitag '51
Duranta repens pigeon-berry
Y
vectors
 Freitag '51
Echinochloa crus-galli water grass
Y (medium)
N
ELISA/culture
RHSS/GSS
 H + P '95
Echinochloa crus-galli water grass
Y
Y
vectors
GSS 
 Freitag '51
Elymus sp.* wild rye*
N
ELISA
 Raju, 1983
Epilobium californicum willow-herb
Y
vectors
 Freitag '51
Epilobium paniculatum panicled willow-herb
Y
vectors
 Freitag '51
Eragrostis diffusa diffuse love grass
Y
vectors
 Freitag '51
Erodium cicutarium red stem filaree
Y
vectors
 Freitag '51
Escallonia montevidensis Escallonia
Y
vectors
 Freitag '51
Eschscholzia californica* California poppy*
N
ELISA
 Raju, 1983
Eugenia myrtifolia Aust. brush-cherry
Y
Y
vectors
BGSS
 Freitag '51
Fragaria californica wild strawberry
Y
ELISA
 Raju, 1983
Franseria acanthicarpa annual bur-sage
Y
vectors
 Freitag '51
Fraxinus dipetala California ash
Y
vectors
 Freitag '51
Fraxinus latifolia Oregon ash 
N
Y (low)
culture
 P + S '99
Fritillaria sp.* fritillary*
N
ELISA
 Raju, 1983
Fuchsia magellanica Fuchsia
Y
vectors
 Freitag '51
Genista monspessulana French broom
Y
Y (med-high)
culture
 P + S '99
Hedera helix English ivy
Y (low-med)
culture
 P + S '99
Hedera helix English ivy
Y
vectors
 Freitag '51
Hedera helix* English ivy*
N
ELISA
 Raju, 1983
Helianthus sp. wild sunflower
N
vectors
GWSS
 Freitag '51
Heteromeles arbutifolia* toyon*
N
culture
 P + S '99
Heteromeles arbutifolia toyon
Y
vectors
 Freitag '51
Hordeum murinum common foxtail
Y
vectors
 Freitag '51
Hordeum nodosum* wild barley*
N
ELISA
 Raju, 1983
Hordeum vulgare barley
Y
vectors
 Freitag '51
Hydrangea paniculata Hydrangea
Y
vectors
 Freitag '51
Juglans californica Calif. black walnut
N
N
culture
 P + S '99
Lactuca serriola prickly lettuce
Y
vectors
 Freitag '51
Lactuca serriola* prickly lettuce*
N
ELISA
 Raju, 1983
Lathyrus cicera Lathyrus
Y
vectors
 Freitag '51
Lathyrus clymenium Lathyrus
Y
vectors
 Freitag '51
Lathyrus sativa grass pea
Y
vectors
 Freitag '51
Lolium multiflorum Italian ryegrass
Y
Y
vectors
GSS/RHSS
 Freitag '51
Lolium temulentum darnel
Y
vectors
 Freitag '51
Lonicera japonica Japanese honeysuckle
Y
vectors
 Freitag '51
Majorana hortensis sweet majoram
Y
vectors
 Freitag '51
Malus sylvestris apple
N
vectors
 Freitag '51
Malva parvifolia cheeseweed
N
vectors
GWSS
 Freitag '51
Matricaria suaveolens pineapple weed
N
vectors
 Freitag '51
Medicago hispida bur clover
Y
vectors
 Freitag '51
Melilotus alba white meliot
Y
vectors
BGSS
 Freitag '51
Melilotus indica hubam clover
Y
vectors
 Freitag '51
Melilotus officinalis yellow sweet clover
Y
vectors
 Freitag '51
Melilotus sp. sweet clover
Y
vectors
 Freitag '51
Melissa offcinalis garden balm
Y
vectors
 Freitag '51
Mentha sp. mint
Y
vectors
 Freitag '51
Mimulus aurantiacus bush monkeyflower
N
vectors
 Freitag '51
Nasturtium officinale* water cress*
N
ELISA
 Raju, 1983
Nerium oleander* oleander*
N
ELISA/culture
 Raju, 1983
Nerium oleander* oleander*
N
culture
 Purcell Î99
Oeanthe sarmetosa water parsley
Y
vectors
 Freitag '51
Oenothera hookeri evening primrose
Y
vectors
 Freitag '51
Parthenocissus quinquefolia Virginia creeper
Y
ELISA/cult./DIF
 Hopkins '88
Parthenocissus tricuspidata Boston ivy
Y
Y
vectors
 Freitag '51
Paspalum dilatatum Dallisgrass
Y
Y
vectors
GSS/RHSS
 Freitag '51
Pelargonium hortorum fish geranium
Y
vectors
 Freitag '51
Pennisetum clandestimun Kikuyugrass
Y
vectors
 Freitag '51
Phalaris minor Mediter. canary grass
Y
vectors
 Freitag '51
Phalaris paradoxa gnawed canary grass
Y
vectors
 Freitag '51
Philadelphus lewisii syringa
N
vectors
 Freitag '51
Phleum pratense Timothy grass
Y
vectors
 Freitag '51
Pittosporum crassifolium karo
Y
vectors
 Freitag '51
Plantago lanceolata English plantain
N
vectors
 Freitag '51
Plantago lanceolata* English plantain*
N
ELISA
 Raju, 1983
Platanus occidentalis sycamore
Y
culture
BGSS
 Hopkins '88
Poa annua annual bluegrass
Y
Y
vectors
 Freitag '51
Poa pratensis* Kentucky bluegrass*
N
vectors
 Freitag '51
Polygonum convolvulus black bindweed
Y
vectors
 Freitag '51
Polygonum persicaria ladys thumb
Y
Y
vectors
 Freitag '51
Polygonum ramosissimum* knot weed*
N
ELISA
 Raju, 1983
Polypogon monspelensis* rabbit foot grass*
N
vectors
 Freitag '51
Populus fremontii Fremont cottonwood 
N
Y (low-med)
culture
 P + S '99
Populus sp.* cottonwood*
N
vectors
 Freitag '51
Portulaca oleracea* common purslane*
N
vectors
 Freitag '51
Prunus armeniaca* apricot*
N
ELISA
 Raju, 1983
Prunus demissa western chokecherry
N
vectors
 Freitag '51
Prunus mume Japanese apricot
N
vectors
 Freitag '51
Prunus sp. wild plum 
Y (low-med)
culture
 P + S '99
Pseudotsuga menziesii* Douglas-fir*
N
vectors
 Freitag '51
Pyracantha augustifolia firethorn
N
vectors
 Freitag '51
Quercus agrifolia coast live oak 
Y
Y (low-med)
Y?
culture
 P + S '99
Quercus domosa* scrub oak*
N
ELISA
 Raju, 1983
Quercus lobata valley oak 
Y (low)
Y (low-med)
culture
 P + S '99
Reseda odorata common migonette
Y
vectors
 Freitag '51
Rhamnus californica* Calif. coffeeberry*
N
culture
 P + S '99
Rheum rhaponticum rhubarb
Y
vectors
 Freitag '51
Rosa californica California wild rose
Y
culture
 P + S '99
Rosa californica California wild rose
Y
vectors
 Freitag '51
Rosa californica* California wild rose*
N
ELISA