Update on Xylella Diseases in Southern California

1. Update on Xylella Diseases in Southern California Frank P. Wong UC Cooperative Extension Specialist Department of Plant Pathology University of California Riverside

4. Xylella Diseases in California One of the most high-profile diseases in the media due to the impact on California viticulture To date more than 700 acres of vines have been destroyed in Riverside Co. alone � nearly $13 million in losses Perceived as a growing threat to other crops as well, including landscape ornamentals

5. Pierce�s Disease

6. History First major outbreak of a Xylella disease in California 1885: 40,000+ acres of grapes destroyed in the Los Angles Basin �Anaheim Disease� 1892 renamed �Pierce�s Disease� of grapevine

7. History 1938: statewide epidemic destroys 60,000+ acres 1940�s: Disease associated with leafhoopers 1970�s: Causal agent finally identified Other strains detected in numerous crop species 1990�s: Arrival of GWSS spreads PD throughout So. Calif.

8. The Pathogen: Xylella fastidiosa

9. The Pathogen: Xylella fastidiosa A small bacteria that lives and multiplies inside of the xylem vessels of plants Very difficult to grow in culture Can live in both mono- and dicotyledenous hosts Primarily vectored by sharpshooter leafhoppers Endemic to the Southeast U.S. Range of disease is limited by range of vector

12. The Role of GWSS in Spreading Xylella fastidosa Glassy-winged sharpshooters arrived in CA in 1990 on nursery stock from the SE Before the introduction of GWSS, Xylella diseases were primarily limited by the habitat and feeding range of the vectors BGSS (Graphocephala atropunctata) West Coast to South America Riparian vegetation GSS (Draeculacephala minerva) California Central Valley Grassland, irrigated pastures, ditch banks RHSS (Carneocephala fulgida) California, Arizona, Northern Mexico Grassland, irrigated pastures, ditch banks

13. Size matters.....

15. GWSS Insect has an extremely broad host range >200 species in >35 families Has the opportunity to spread the pathogen to many different host plant species. List of feeding and oviposition hosts at http://www.cdfa.ca.gov

17. How do insects �cause� disease? Sharpshooters can transmit the bacteria that causes PD GWSS happens to be extremely good at it (a good vector) A good vector + broad host range + plenty of susceptible hosts = nice disease epidemic

18. Bacteria Transmission Piercing-sucking mouthparts Feed on xylem

19. Vector-Pathogen Interaction: Acquisition

20. Vector-Pathogen Interaction: Acquisition

21. Vector-Pathogen Interaction: Acquisition and Feeding

22. Vector-Pathogen Interaction: Acquisition

23. Vector-Pathogen Interaction: Incubation and Reproduction

24. Vector-Pathogen Interaction: Transmission

25. Vector-Pathogen Interaction: Transmission and Infection

26. Vector-Pathogen Interaction: Pathogen Reproduction in Host

27. How the Pathogen Causes Disease Bacterium reproduces in xylem only Forms aggregates that block xylem and water movement Plant also tries to defend itself by producing gums and tyloses to seal off infected areas Overall effect is the stoppage of water flow to the plant

28. The Pathogen: Xylella fastidiosa

32. Symptoms Decreased water movement causes symptoms that often look like water stress or nutrient deficiency Scorch Chlorosis Stunting Decline Usually appear in summer and fall during periods of heat and water stress Symptoms can manifest as delayed growth in spring

37. Strains of X. fastidiosa Strain-host specificity not well understood At least 9 groups identified PD-strains grape, almond, alfalfa Almond Leaf Scorch almond, grape Oak Leaf Scorch oak Phony Peach peach, plum? Mulberry Maple Leaf Scorch maple Oleander oleander, periwinkle Citrus Varigated Chlorosis citrus, grape Plum Scald plum, peach?

38. X. fastidiosa in Landscape Ornamentalsin the Eastern U. S.

39. Xylella Diseases in California

42. ELISA results 2003

44. Oleander Leaf Scorch

48. Olive Leaf Scorch

57. Liquidambar Dieback and declines observed in Riverside in late-1990�s Tested positive for Xylella in 2000 (Don Ferrin) and 2002 (Heather Costa) No scorch seen, just death of upper canopy Role of bacterium not yet confirmed

60. Ornamental Plum

64. Almond Leaf Scorch

69. Magnolia grandifloraSouthern Magnolia

74. Control This will be a big challenge to California A lot of basic science needs to be worked out especially outside of the grape world Tetracycline injections appear to alleviate symptoms � but costly and repeat applications are needed Vector control difficult due to efficiency of transmission

75. Control Irrigation management may help alleviate symptoms Host susceptibilities still being examined How do you examine thousands of landscape ornamentals?

78. ELISA (Enzyme Linked Immunosorbent Assay) Immunological reaction: bacteria are bound to antibody-coated wells Color change indicates presence of X. fastidiosa Good for initial screening Commercial Kits: relatively fast and simple to use Sometimes have false positives Does not indicate strain

79. Extract bacterial DNA from plant tissue or media culture Amplify a DNA fragment using primers specific for X.f. More time consuming and expensive than ELISA Need specialized equipment Can provide preliminary strain identification PCR (Polymerase Chain Reaction)

80. Media Culture Isolate pathogen on sterile media Slow process, often get contamination Best way to get a large amount of pure bacterial DNA for sequencing Still need further testing to confirm, and ID strain Can use cultures to mechanically inoculate plants

81. Outlook Millions of dollars are being directed towards Xylella and GWSS research in California over 50 funded projects specific for landscape: 1 (although there are crossovers) Full genome of bacterium sequenced A big challenge indeed

82. Outlook Specifically for landscape: Surveys and detection need to be formally conducted Need idea of impact and severity in landscape Need more information on how SE US deals with problem Keep your eyes open