Bacterial Wilt and Bacterial Leaf Scorch on Blueberry in Florida. Deanna Bayo Ph.D. Student Phil Harmon, Ph.D. UF/IFAS Plant Pathology Department

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1 Bacterial Wilt and Bacterial Leaf Scorch on Blueberry in Florida Deanna Bayo Ph.D. Student Phil Harmon, Ph.D. UF/IFAS Plant Pathology Department

2 Bacterial leaf scorch Bacterial leaf scorch caused by Xylella fastidiosa First occurred around 2004 Certain varieties are susceptible Primarily spread via an insect vector (sharpshooters) Few management options available, insecticide applications of limited usefulness

3 Bacterial Leaf Scorch (Xylella fastidiosa) Grafted (MG) Own-rooted (MO)

4 Bacterial leaf scorch 25% 50% 88%

5 Bacterial leaf scorch Own-rooted Meadowlark were more susceptible to BLS than those grafted onto V. arboreum rootstocks. Grafted plants become infected with the BLS pathogen, but when detected, titers of X. fastidiosa were significantly lower in grafted plants than in own-rooted stems. X. fastidiosa was not detected in V. arboreum roots of grafted Meadowlark plants but was detected in roots of own-rooted Meadowlark.

6 Bacterial Wilt Caused by Ralstonia solanacearum Soil-borne bacterium with a wide host range Common scourge of tropical agriculture Very difficult to control where it occurs Infects a wide host range of 250 species in 54 families First reported in Florida in 1897 on tomato Occurs commonly on tomato and potato (brown rot) Occasional problem of eggplant and tobacco in the last 100 years

7 Bacterial Wilt Previously reported on blueberry only once (in New Jersey in 2012) Cultivar Bluetta was affected 20 year-old bushes rapidly died Quarantine and eradication efforts ensued Little else known about that occurrence USDA APHIS have cultures of the strain responsible

8 Bacterial Wilt in Florida Found on 5 Florida Blueberry farms in were in production fields, 1 in a nursery All finds were on the variety Arcadia All plants were 1.5 to ~2 yrs old All plants were from the same nursery source One additional farm so far (3/16) in 2017 Two additional varieties on a farm: Kestrel and Avanti (no obvious genetic link to Arcadia)

9 Ralstonia in Florida Isolates from 6 blueberry farms ranging from Alachua Co. to Hendry Co. are being characterized Isolates vary genetically between 3 of the 4 farms, but all have tested negative for Race 3 biovar 2 Because isolates vary, it is unlikely they all came from a single source (nursery) Should Arcadia still be recommended? Bacterial wilt poses a serious risk for this variety It s not the only one that can get the disease

10 Regulatory/Quarantine FDACS DPI and APHIS were notified The nursery positive cooperated with FDACS regulatory Extensive samples were taken by Dr. Xiaoan Sun and inspectors, the regulatory case was closed FDACS DPI has requested that all new positives in the plant disease clinic continue to be reported

11 Survival and introduction The bacterium is soil and waterborne Once introduced it can survive for years in infested waters including ponds and rivers and in wet soils deeper than 30 in It can survive in plant material without causing symptoms (latent infection) It can survive in weedy hosts (primarily solanaceous, like nightshade)

12 Infection Occurs primarily through roots Wounds formed by lateral root emergence Wounds formed by root damage or feeding (root knot nematode and others) Infection of wounds in stems is also possible Pruning wounds Insect feeding Infection and disease occurs at temperatures above 75F and below 95F Once in the plant, the bacterium spreads through the vasculature

13 Symptoms Similar to bacterial leaf scorch (Xylella) marginal scorching of leaves, dieback, stem blight, plant death symptoms move down the row more rapidly than across Xylem of plants loaded with bacterial ooze clogging vasculature causing wilt

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20 Testing for Ralstonia look for symptoms similar to Xylella, but running down a row or in large circular areas in fields the cultivar Arcadia is known susceptible send samples to the UF IFAS Plant Diagnostic Center in Gainesville, UF/IFAS Plant Diagnostic Center Bldg. 1291, 2570 Hull Road Gainesville, FL pfharmon@ufl.edu

21 Streaming test Immunostrip test PCR confirmation Testing for Ralstonia

22 Management Exclude the pathogen from your farm Avoid movement of soil and water onto the farm Sanitize equipment, tools (bleach, alcohols, peroxides) Do not use surface/recycled water for irrigation Purchase clean, healthy plant material

23 Management Propagation measures to prevent bacterial wilt in nurseries Do not use surface water for irrigation Use well or municipal water rather than ebb and flood systems, or monitor and sanitize water Do not allow soil contact with cuttings (use benches) Keep production areas free of weeds and other potential host plants, particularly solanaceous (Nightshade)

24 Management Host plant resistance Arcadia, Kestrel, and Avanti are the known susceptible SHB, there will be more Resistance in other crop plants has had minimal impact where the disease occurs Resistance hasn t held over time or in different areas Screening protocols will be incorporated in the UF IFAS blueberry breeding program Need more research in this area, more time

25 Management ph, rotation, cover crops High ph soil inhibits the bacterium but blueberry require low ph Blueberry is a perennial crop so rotation is not an option Co-cropping and cover cropping also are not viable options Do not plant in infested fields The disease is also known as Granville wilt, after the town in NC where hundreds of tobacco farms were abandoned due to the disease

26 Management Chemical and fumigation options Broad spectrum fumigants like methyl bromide, chloropicrin, 1,3D, and botanicals (Thymol) can reduce nematodes and bacterial populations, but the bacterium survives at depths below the treated soil, these products are increasingly difficult to find/use and are very costly Soil drench and through-irrigation applications of phosphonate fungicides have reduced infection in vegetable and ornamental crops

27 Management EDIS publication: K-Phite is an example product that is labeled for the disease and for blueberry chemigation 2 to 4 quarts in at least 200 gal of water per acre drench 2 to 4 quarts in at least 100 gal of water banded application 2 to 4 quarts in at least 20 gal of water followed by light irrigation 7 to 28 day interval

28 Protection options no data on blueberry Management these methods were shown effective preventing infection of geranium grown in infested soil they do not cure infected plants

29 Ongoing Research

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31 Ongoing Research 15 cultivars (14 UF SHB, Bluetta) ~5 weeks for symptom development ~12+ days for plant death Almost all tested cultivars are susceptible (not detected in Meadowlark so far)

32 Repeat! Determine differences in susceptibility links in parent lines? Management options Phosphorous acids or salts (eg. K-phite) determine effectiveness Oxytetracycline? Streptomycin? What s next?

33 Any Questions? Philip Harmon, University of Florida Deanna Bayo, University of Florida