Texas Phoenix Palm Decline Phytoplasma

California Pest Rating for

Texas Phoenix Palm Decline Phytoplasma

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

During the month of February 2014, CDFA Plant Pathologist Dr. Cheryl Blomquist was notified by Dr. N. Harrison, Plant Pathologist, University of Florida, Fort Lauderdale of palm stem tissue samples he had received from a California private palm grower whose date palms had been dying for the past several years. Dr. Harrison analyzed the samples to be positive for the Texas Phoenix Palm Decline disease (TPPD). Dr. Blomquist followed through by contacting the private grower in Desert Hot Springs, Riverside County, CA to assess the palm disease situation at her site and with a request for CDFA to collect samples to send to the USDA diagnostic laboratory for testing. The grower obliged and further mentioned two other sites in Riverside County (one in Palm Desert: a mobile home community with a golf course; one date farm in Sky Valley) where she had noticed symptoms of palm decline similar to those observed in palm trees at her site (Blomquist, 2014). CDFA Plant Pathologist Magally Luque-Williams collected official samples from the locations at Desert Hot Springs (1date palm tree) and Palm Desert (2 queen palm trees). Those samples were submitted for analysis to the USDA CPHST Beltsville Laboratory, however, due to delayed shipping and poor quality of the received samples, the results were negative for TPPD. Subsequently, re-samples taken from the same locations (2 trees at each location) and resubmitted to the Beltsville Laboratory were also declared negative for TPPD. Palm trees at the date farm in Sky Valley were not officially sampled due to objection raised by the property owner. An assessment of the risk presented by TPPD in California is herein conducted to propose an official rating.

History & Status:

Background: Texas Phoenix Palm Decline disease is caused by a phytoplasma which has been classified as a member of 16S rDNA RFLP group 16SrIV, subgroup D (16SrIV-D). The TPPD phytoplasma is related to, but genetically distinct from the phytoplasma that causes lethal yellowing in palms. It was originally identified in 2001 on Phoenix canariensis (Canary Island date palm) grown in the southern coastal region of Texas, hence the name of the disease. Texas Phoenix Palm Decline has only been reported from the USA, specifically from Texas, Florida and most recently from Louisiana (LSU AgCenter, 2014).

Hosts: Currently, susceptible hosts for the TPPD phytoplasma are Phoenix dactylifera (date palm), P. canariensis (Canary Island date palm), P. sylvestris (silver or Sylvester date palm), P. reclinata (Senegal/wild date palm), Sabal palmetto (cabbage/sabal palm), and Syagrus romanzoffiano (queen palm).

Symptoms: TPPD chronologically progresses through a series of symptoms so that no single symptom is diagnostic of the disease. The first obvious symptom on mature palms is premature drop of most or all fruits over a period of a few days and not over a prolonged period of time. Inflorescence necrosis follows fruit drop. However, fruit drop and inflorescence necrosis only occurs if the palm is mature enough to produce fruit, it is the season for flowering and fruiting, and the flowers or fruits have not been trimmed from the plants. The next symptom is the discoloration of foliage beginning with the oldest leaves and beginning at leaf tips. Instead of turning yellow or only turning yellow for a brief period, the leaves turn varying shades of reddish-brown to dark brown or gray. Unless monitored carefully, leaf discoloration may often be confused with natural senescence or senescence caused by nutritional deficiency, Lethal yellowing (phytoplasma disease) or Gandoderma butt rot (fungal disease causing dry rot within trunks of palms). However, with TPPD, there are a greater number of dead older leaves than normal for natural senescence. This symptom may easily be overlooked if dying or dead leaves are regularly removed from diseased trees. The death of the spear leaf is the next symptom. This may occur in Phoenix species when less than one-third or one-quarter of the oldest leaves have discolored and turned necrotic, and in cabbage palms when about two-thirds of the oldest leaves have discolored. Death of the spear leaf means death of the apical meristem. Once that happens, no new leaves will develop and the remaining leaves from the oldest to the youngest will continue to discolor and die. Death of the spear leaf is not always obvious and unless it is dead, hanging from the canopy, or on the ground, it will require close examination to determine if it is healthy or not. Sometimes, by the time spear leaf dies, mature palm roots at or near the soil surface are soft in texture and easily broken. The rooting root system enables such plants to be easily rocked back and forth in the ground (Harrison & Elliott, 2009).

The TPPD phytoplasma is usually not detectable in palms that are not showing symptoms and may not be detectable until the spear leaf dies (Harrison & Elliott, 2009)

Texas Phoenix Palm Decline is a fatal disease. The phytoplasma colonizes the phloem (vascular) tissue so that it spread systemically and quickly kills palms.

Transmission: The TPPD phytoplasma is spread naturally by piercing-sucking, insects, feeding on phloem sap. The species of the insect vector is not known, however, plant hoppers, psyllids or treehoppers are the most-likely groups of insects to transmit the TPPD phytoplasma. The phytolasma is spread from plant to plant through the feeding activities of these insects and does not survive outside their plant or insect host. Also, TPPD is spread through human activity which causes the movement of vector and infected hosts.

Worldwide Distribution: Texas Phoenix Palm Decline disease has only been reported from the USA. Within the USA, it has been reported from Texas, Florida and Louisiana.

Official Control: Texas established quarantine regions and imposed the “Texas Date Palm Lethal Decline Quarantine” requiring phytosanitary certification of imported palms from the state of Florida. (Under the Texas Lethal Yellowing quarantine date palm- another existing quarantine for palm trees – Phoenix dactylifera; Canary Island date palm, Phoenix canariensis; and silver date palm, Phoenix sylvestris are prohibited entry from Florida, the Commonwealth of Puerto Rico and Territory of Guam.)

California Distribution: Texas Phoenix Palm Decline Phytoplasma was not detected in official samples collected in Riverside County (see ‘Initiating event’) and therefore, there is no official record of the presence of TPPD within California. Nevertheless, as also detailed above in ‘Initiating event”, the detection of TPPD in a non-official sample initially analyzed by Dr. Harrison (University of Florida), suggests the presence of TPPD in diseased date palms cultivated by a private owner. Further investigation of several trees will be necessary to establish this as fact.

California Interceptions: There have been no interceptions of TPPD in California.

The risk Texas Phoenix Palm Decline phytoplasma would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.

Risk is High (3) – TPPD is likely to establish wherever date palms are grown in California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is Medium (2) – Thus far, susceptible hosts of TPPD include date, cabbage and queen palms – although these hosts are widely grown mainly in Southern California.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Although the exact species of the vector is not known, the group of leafhoppers, treehoppers or psyllids as possible vectors of the TPPD phytoplasma render the TPPD phytoplasma a relatively high potential for increase and dispersal to non-infected sites.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.

Risk is High (3) – TPPD phytoplasma kills palms thereby, causing losses in date fruit yields, increases in crop production, loss of date fruit and ornamental palm markets, impositions of necessary quarantines, plus the phytoplasma is vectored by sap-sucking insects.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.

Risk is High (3) – Palms infected by the TPPD phytoplasma could trigger additional official and private treatment programs, impact cultural practices, home/urban gardening and ornamental plantings and disrupt natural communities of palm growth in California.

Consequences of Introduction to California for Texas Phoenix Palm Decline:

Add up the total score and include it here. (Score)

– Low = 5-8 points
– Medium = 9-12 points
– High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Texas Phoenix Palm Decline phytoplasma to California = (14).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

– Not established (0) Pest never detected in California, or known only from incursions.
– Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
– Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
– High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is (-0). TPPD phytoplasma has never been officially detected in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 14.

Uncertainty:

Texas Phoenix Palm Decline Phytoplasma has not been officially detected in California. Only a few trees were sampled from the suggested sites (see ‘Initiating event’). To fully establish the possible presence and distribution of the pathogen, more complete and timely surveys of several symptomatic palm trees from those and possibly other sites would be necessary. Also not known is the specific identity of the insect vector involved. Leafhoppers are considered the most likely vector, however, their distribution, host preferences and other aspects of biology would directly impact the current knowledge of the TPPD phyoplasma.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Texas Phoenix Palm Decline is A.

References:

Blomquist, C. 2014. Emails to and from (private grower) dated February 12-13, 2014.

Harrison, N.A. and M.L. Elliott. 2007. Texas Phoenix palm decline. University of Florida, IFAS.
http://edis.ifas.ufl.edu/PP163.
http://www.pest-control-tampa.com/pest-news/081219_TPD_EmergencyQuarantine.pdf

LSU AgCenter, 2014. http://www.lsuagcenter.com/news_archive/2014/January/headline_news/Fatal-palm-disease-detected-in-New-Orleans.htm

Symptoms of diseases and disorders – Fact sheet: Texas Phoenix Palm Decline http://itp.lucidcentral.org/id/palms/symptoms/Texas_Phoenix_Palm_Decline.htm
Texas Department of Agriculture. Date Palm Lethal Decline. http://www.texasagriculture.gov/RegulatoryPrograms/PlantQuality/PestandDiseaseAlerts/DatePalmLethalDecline.aspx

Responsible Party:

Dr. John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.