Sampling for Xylella fastidiosa the Cause of Bacterial Leaf Scorch

1. Sampling for Xylella fastidiosa the Cause of Bacterial Leaf Scorch Dr. Frank Wong Dr. Naveen Hyder Department of Plant Pathology & Microbiology

2. Bacterial leaf scorch and dieback are becoming increasingly common in California Agricultural crops such as grapes, almonds and olives are at risk Landscape plants such as oleander, liquidambar and purple plum are also being affected The disease causes scorch and dieback and is often fatal to the plants

3. These diseases are caused by the xylem-limited bacteria Xylella fastidiosa which grows inside the plant and kills it by limiting or blocking water movement in these vessels The main method in which these bacteria spread are by sharpshooter insects which vector the bacteria though their mouthparts from plant to plant as they feed

4. Testing for X. fastidiosa Confirming the presence of Xylella fastidiosa in a plant is important for making the right management choice Symptoms can be often confused with water stress or other environmental factors Xylella fastidiosa is too small to be diagnosed from plants by eye or most microscopes There are three testing methods available Enzyme Linked Immunosorbent Assay (ELISA) Polymerase Chain Reaction (PCR) Direct isolation and culturing of the bacteria

5. ELISA The most common test used Similar to HIV testing Takes 1 to 2 days to complete Bacteria is extracted from plant tissue and can stick to antibodies bound to plastic plates A detectable, second antibody is used to tag the bound bacteria

6. PCR Testing Bacterial DNA is extracted from plant tissue and diagnostic primers are used to amplify only the Xylella fastidiosa DNA Amplified products are visualized by gel electrophoresis More sensitive than ELISA, but more expensive

7. Isolation & Culture The most time consuming testing method (often 4 or more weeks) Bacteria is extracted from the plants and put onto specialized media The bacteria is hard to grow in culture and can often be overgrown with contaminants Isolation is essential for characterizing new strains

8. Sampling Good samples with live bacteria are needed for any of the testing methods Live bacteria are most likely to be found in diseased, but live plants Green stems, petioles and leaf midveins are often the best choice for tetsig

9. The best samples are those that are symptomatic but still intact and turgid (top) Samples from very symptomatic plants can often be too dried out or full of secondary microbes (middle) Testing cannot be done on tissue that is completely dead (bottom)

10. How to Send Samples? Only a few grams of green stems or petioles are needed for testing A few 6-inch pieces of good samples are often more than enough Tissue must be kept moist and not allowed to mold in transit Place samples in a plastic bag with a moist towel and sent by overnight mail for the best chances of having a good test done

11. Where to Send Samples? Dr. Frank Wong 900 University Avenue University of California Department of Plant Pathology & Microbiology 204 Fawcett Lab Riverside, CA 92521 frank.wong@ucr.edu naveen.hyder@ucr.edu 951-827-2936 Walk-in samples are always welcome Fill out the information forms available at www.xylella.org or here