Seed-Borne Disease with Jodi Lew-Smith


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  • dwarfism, mosaic, distorsion and yellowing of the leaves with sometimes a very reduced lettuce heart
  • dwarfism, mosaic, distorsion and yellowing of the leaves with sometimes a very reduced lettuce heart
  • Bacterial blight, caused by Xanthomonas campestris pv. Carotae
  • Hot water treatment of vegetable seeds to eradicate bacterial plant pathogens in organic production systems [Online]. S. Miller and M. Lewis Ivey. 2005. Ohio State Extension Bulletin HYG-3086-05. Available at: (verified 10 March 2010).
    Seedborne diseases and their control: Principles and practice. R.B. Maude. 1996. CAB International, Tucson, AZ.
  • Seed-Borne Disease with Jodi Lew-Smith

    1. 1. SEED-BORNE DISEASE AND YOU Jodi Lew-Smith, Ph.D. High Mowing Organic Seeds
    2. 2. Insert slide about prevention of disease in organics • Note that bacterial diseases tend to be systemic, highly virulent, and rarely treatable in fields, but can be treated by hot water if present in small amounts on seed—though this isn’t advised for the more virulent pathogens. Fungal diseases tend to be more topical and treatable in fields, but can be harder to eradicate on seed and can be highly virulent. Viruses are less destructive in fields but are not treatable at any time and must be handled by prevention.
    4. 4. BACTERIA simple cells with ‘soft’ cell walls, mostly have to stay moist at all times – so live INSIDE of plants -Hard to stop in the field – get into plant veins and tend to travel throughout whole plants (systemic) -Likely to get INTO seed because systemic -Easier to treat inside seed than fungi, as more sensitive to heat Xanthomonas campestris From Muirbiology Institute of Cell and Molecular Biology, The University of Edinburgh
    5. 5. FUNGI complex cells with hard (chitin) cell walls, spread by spores and tend to colonize OUTSIDE of plants -Easier to set back in field – often on plant surfaces -Variable entry into seed -Variable success in treating on seed (some more sensitive to heat than others) -Can live in soil, but usu.insignificantly seed-borne if soil-borne Botrytis cinerea on lettuce seed From Muirbiology Photo High Mowing Seeds
    6. 6. VIRUSES packaged DNA or RNA – no cells –hard to ‘kill’ (very different from other two) - Impossible to stop in field Impossible to treat in seed Often less devastating as diseases go Easier to detect before planting – strip tests From Muirbiology From Cornell Cooperative Extension
    7. 7. As a seed grower, what do I need to worry about? • RED ALERT diseases: = highly virulent, highly seed-borne • ORANGE ALERT diseases: = moderately virulent, highly seed-borne OR highly virulent, moderately seed-borne • YELLOW ALERT diseases: = moderate or weakly virulent, moderate or weakly seed-borne (I won’t talk about these today)
    8. 8. Luckily… • There are only a handful of red alert diseases. • The worst of which is…
    9. 9. Brassica BLACK ROT BACTERIA (Xanthomonas campestris) – RED ALERT – Highly virulent, highly seed-borne – Distinction of being #1 among top ten seed-borne diseases – Spreads quickly in warm, humid weather – New strip test available from Agdia – Sensitive to hot water treatment
    10. 10. BLACK ROT SYMPTOMS Spreads rapidly in warm, humid weather
    11. 11. BLACK ROT SYMPTOMS UNH Cooperative Extension Leaf margins, primarily veins
    12. 12. Brassica BLACKLEG FUNGUS (Phoma lingam / Leptosphaeria maculans ) – – – – – RED ALERT (#2 for Brassicas) Highly virulent, highly seed-borne Spreads quickly in warm, humid weather Not as common or explosive as Black Rot Sensitive to hot water treatment
    13. 13. BLACKLEG SYMPTOMS Ontario Ministry of Agriculture Stem cankers encircle stems, typically at base, black pycnidia visible within cankers
    14. 14. BLACKLEG SYMPTOMS Dark grey lesions on roots, eventual spots on leaves
    15. 15. Lettuce Mosaic Virus – RED Alert – Highly virulent, highly seed-borne – Very common, especially on the west coast – Spreads by insects, mainly leaf hoppers – Not as deadly as fungal or bacterial diseases – low levels can be tolerable
    16. 16. LETTUCE MOSAIC VIRUS SYMPTOMS Difficult to distinguish from CMV in fields, but tests are readily available
    18. 18. Carrot BACTERIAL BLIGHT • BACTERIA (Xanthomonas campestris pv. carotae) – Orange Alert – Moderately virulent, highly seed-borne – Primarily causes yield losses due to poor seed germination
    19. 19. Bacterial Blight symptoms Lesions turn dark brown and shiny, and progress down petiole
    20. 20. Carrot FUNGAL BLIGHTS FUNGUS • ALTERNARIA BLIGHT (Alternaria dauci, also A. radicina) • CERCOSPORA BLIGHT (Cercospora carotae) – Orange Alert - Moderately virulent, moderately seedborne - Can occur in the same field, cause yield losses due to leaf loss
    21. 21. Cercospora Blight symptoms Spots more round, better defined
    22. 22. Alternaria Blight symptoms Lesions more irregular, typically on margins
    23. 23. Onion WHITE ROT FUNGUS (Sclerotium cepivorum, Sclerotinia sclerotiorum) – Orange Alert – Doesn’t actually travel on seed, but black sclerotia can easily get mixed with seed because they look so similar – Most prevalent in cool seasons and poorlydrained fields – Sclerotia can persist in soil for up to fifteen years
    24. 24. White Rot Symptoms
    25. 25. White Rot Symptoms Fluffy white mold, black spores and sclerotia
    26. 26. TOMATO MOSAIC VIRUS Effectively same as Tobacco Mosaic Virus - Red Alert - Highly virulent, highly seed-borne - Commercial damage may range from light to heavy, but disease extremely hard to eradicate from seed - Good strip test available from Agdia
    27. 27. Tomato Mosaic Virus symptoms
    28. 28. TOMATO BACTERIAL DISEASES BACTERIA Bacterial canker michiganense), (Corynebacterium michiganense pv. Bacterial Spot (Xanthomonas campesiris pv, vesicatoria) Bacterial Speck (Pseudomonas syringae pv. tomato) Orange Alert - Highly to moderately virulent, highly seedborne - Cause considerable damage, esp. in GH’s - eradicated from seed by fermentation and/or hot water treatment
    29. 29. Bacterial Canker Symptoms D. Cuppels, Agriculture & Agri-Food Canada, via BC Ministry of AG Round, pale, “birdseye” spots Cornell Cooperative Extension
    30. 30. Bacterial Spot Symptoms Sherrie Smith, Univ. Ark From Plant Health Progress article Scabby, raised spots. Infects green fruit.
    31. 31. Bacterial Speck Symptoms Univ of FL extension Spots smaller, more shallow
    32. 32. Comparative Symptoms Illinois Fruit and Vegetable News Spots most distinctive features, leaf and stem symptoms often similar
    33. 33. What is a grower’s responsibility with respect to seed-borne disease? • Knowledge of which diseases are seed-borne • Careful scouting of crops to spot symptoms • Confirmation of diagnosis with Extension or other diagnostic service if symptoms appear • Consultation with seed company to determine course of action
    34. 34. What are the scenarios when I find ANY kind of disease in a seed crop?
    35. 35. I. If it’s NOT a seedborne disease: Apply treatment to keep the plants alive (E.g. late blight of tomato)
    36. 36. II. If it’s a disease of LOW virulence: AND the seed could be treated, it may be harvested and flagged for hot water treatment E.g. possible for some bacterial spot diseases in tomato or pepper
    37. 37. III. For MOST seed-borne diseases: The crop is typically destroyed as soon as disease confirmed Avoids spending any more time or money on a crop that won’t make saleable seed
    38. 38. SEED TREATMENTS FOR DISEASE ERADICATION • Hot Water • Bleach • Experimental treatments
    39. 39. HOT WATER TREATMENT • Advantages: – – – – Most effective Kills disease on both inside and outside of seed Can fully eradicate heat-sensitive pathogens no residue • Disadvantages: – requires an investment – Requires careful handling, can damage seed – Can’t be done as easily during harvest, so often requires wetting and re-drying seed
    40. 40. Hot Water Requirements 42-50°C (118-122°F) 15-25 minutes Seed fully immersed, typically in cotton bags NEED a setup with temperature control Budget option is deep fryer (~$50-150) Better option is a lab-grade water bath incubator (~150-800 on ebay) • Does NOT damage seed if done carefully • • • • • •
    41. 41. Shaking Water bath
    42. 42. Bleach Treatment • Advantages: – – – – Fast, easy, requires little to no special equipment Can be done during washing of wet-seeded crops Good for reduction but not eradication of disease Only organic option for large-seeded crops that can’t be hot water treated • Disadvantages: – Not likely to completely eradicate disease – Requires careful handling, can damage seed coat – Kills disease only on seed coat, not internally
    43. 43. Bleach Requirements • Soak seed in a 5-10% bleach solution • usually 5-10 minutes • Can be done by adding bleach to final wash on wet seed harvest
    44. 44. Other Treatments • Natural II • Biocontrol agents, e.g. Efficacy can be good, but mostly for improved germination – i.e. not appropriate for eradication of virulent seed-borne diseases
    45. 45. Print Resources • • • • • • • • • • • • • • 1. Common Laboratory Seed Health Testing Methods for Detecting Fungi . 2003. S.B. Mathur, O. Kongsdal. The International Seed Testing Association. Bassersdorf, CH-Switzerland. 2. Crucifer Diseases: A Practical Guides for Seedsmen, Growers, and Agricultural Advisors. 1994. J. Cucuzza, J. Dodson, B. Gabor, J. Jiang, J. Kao, D. Randleas, V. Stravato, and J. Watterson. Plant Pathology Department, Petoseed Company, Inc. Saticoy, California. 3. The Diagnosis of Plant Diseases: A Field and Laboratory Manual Emphasizing the Most Practical Methods for Rapid Identification. 1972. R.B. Streets, Sr. The University of Arizona Press, Tucson, Arizona. 4. Diseases and Pests of Vegetable Crops in Canada: An Illustrated Compendium . 1994. R.J. Howard, J.A. Garland, W.L. Seaman, Eds. The Canadian Phytopathological Society and the Entomological Society of Canada. M.O.M. Printing Ltd. Ottawa, Ontario, Canada. 5. Hortus Third, A Concise Dictionary of Plants Cultivated in the United States and Canada. 1976. L. H. Bailey. Macmillan Publishing. New York, New York. 6. Identifying Diseases of Vegetables. 1994. A.A. MacNab, A.F. Sherf, J.K. Springer. Penn State College of Agricultural Sciences. University Park, Pennsylvania. 7. Illustrated Genera of Imperfect Fungi, 4th Edition. 1998. H.L. Barnett, B.B. Hunter, The American Phytopathological Society. APS Press. St. Paul, Minnesota. 8. Laboratory Guide for Identification of Plant Pathogenic Bacteria, 3rd Edition. N.W. Schaad, J.B. Jones, W. Chun, Eds. The American Phytopathological Society. APS Press. St. Paul, Minnosota. 9. Plant Pathology, 3rd Edition. 1988. G.N. Agrios. Academic Press, Inc. San Diego, California. 8. Principles of Seed Pathology, 2nd Edition. 1996. V.K. Agarwal, J.B. Sinclair. CRC Press, Inc., Lewis Publishers. Boca Raton, Florida. 10. Rules for Testing Seeds. 1999. Association of Official Seed Analysts. Lincoln, Nebraska. 11. Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners , 2nd Edition. 2002. S. Ashworth. Seed Savers Exchange, Inc. Decorah, Iowa. 12. Tomato Diseases: A Practical Guides for Seedsmen, Growers, and Agricultural Advisors. 1997. B. Gabor and W. Wiebe, Eds. Plant Pathology Department, Seminis Vegetable Seeds, Inc. Saticoy, California. 13. World Economic Plants: A Standard Reference. 1999. J. H. Wiersema and B. Leon. Agricultural Research Service, United States Department of Agriculture. CRC Press, Inc. Boca Raton, Florida.
    46. 46. Online Resources • • • • • • • • • • • • • • • Common Names of Plant Diseases Cornell University’s Plant Disease Diagnostic Clinic Homepage Simplified Fungi Identification Key SBML Fungal Databases – Selecting Fungus-Host Distributions Vegetable Diseases Fact Sheets listed by Crop Plant diseases directory for agricultural crops – Manitoba agriculture, food, and rural initiatives Plant Disease Information System Seedborne diseases and their control: Principles and practice. R.B. Maude. 1996. CAB International, Tucson, AZ. Hot water treatment of vegetable seeds to eradicate bacterial plant pathogens in organic production systems [Online]. S. Miller and M. Lewis Ivey. 2005. Ohio State Extension Bulletin HYG-3086-05. Available at: (verified 10 March 2010).
    47. 47. THANK YOU! Seed Art