SEED-BORNE DISEASE AND YOU

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SEED-BORNE DISEASE AND YOU
Jodi Lew-Smith High Mowing Seeds
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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

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BRASSICA TOP SEED-BORNE DISEASES

• 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
• BLACKLEG fungus (Phoma lingam / Leptosphaeria
  maculans )
• RED ALERT
• Highly virulent, highly seed-borne
• Spreads quickly in warm, humid weather

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MORE BRASSICA SEED-BORNE DISEASES

• ALTERNARIA DISEASES
• Orange Alert
• Three different species, all similar for purposes
  of control
• Less virulent than former two, but can be
  seed-borne and should be controlled

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BLACK ROT SYMPTOMS
Spreads rapidly in warm, humid weather
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BLACK ROT SYMPTOMS
Leaf margins, primarily veins
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BLACKLEG SYMPTOMS
Stem cankers encircle stems, typically at base,
black pycnidia visible within cankers
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BLACKLEG SYMPTOMS
Dark grey lesions on roots, eventual spots on
leaves
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ALTERNARIA SYMPTOMS
Classic bullseye spot on leaves
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ALTERNARIA SYMPTOMS
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BRASSICA SEED-BORNE DISEASE CONTROL

• Obtain disease-free seed, do not take any
  chances, heat-treat seed for additional security
• Make sure all crop debris is completely
  incorporated and/or removed
• Avoid dense plantings, avoid working in wet
  fields
• Practice 4-year rotation with eradication of all
  crucifer weeds before planting brassica seed
  crops again
• Preventive copper sprays

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LETTUCE TOP SEED-BORNE DISEASE

• LETTUCE MOSAIC VIRUS (LMV)
• RED Alert
• Highly virulent, highly seed-borne
• Very common, especially on the west coast
• Spreads by insects, mainly leaf hoppers

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LETTUCE MOSAIC VIRUS SYMPTOMS
Difficult to distinguish from CMV in fields, but
tests are readily available
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LETTUCE MOSAIC VIRUS SYMPTOMS
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LETTUCE MOSAIC CONTROL

• Primary control is disease-free seed
• Seed testing is widely available
• Once confirmed in MTO seed field, plants are
  destroyed
• Tolerance for low levels in non-MTO crops

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CARROT TOP SEED-BORNE DISEASES (LEAF BLIGHTS)

• BACTERIAL BLIGHT bacteria (Xanthomonas campestris
  pv. carotae)
• Orange Alert
• Moderately virulent, highly seed-borne
• Primarily causes yield losses due to poor seed
  germination
• ALTERNARIA BLIGHT fungus (Alternaria dauci, also
  A. radicina) and CERCOSPORA BLIGHT fungus
  (Cercospora carotae)
• Orange Alert
• - Moderately virulent, moderately seed-borne
• - Can occur in the same field, cause yield loss
  due to leaf loss

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Bacterial Blight symptoms
Lesions turn dark brown and shiny, and progress
down petiole
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Cercospora Blight symptoms
Spots more round, better defined
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Alternaria Blight symptoms
Lesions more irregular, typically on margins
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CARROT LEAF BLIGHT CONTROL

• Obtain disease-free seed, heat treat where
  possible for added security
• Avoid overhead irrigation
• Avoid working in wet fields
• Allow 2-year rotation for debris to break down in
  field
• Avoid highly-susceptible varieties which increase
  inoculum levels
• Preventive copper sprays

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ONION TOP SEED-BORNE DISEASES

• BOTRYTIS NECK ROT fungus (Botrytis allii, also B.
  aclada and B. byssoidea) (Disease also called
  SCAPE AND UMBEL BLIGHT)
• Orange Alert
• Highly virulent, degree of seed transmission
  disputed
• Causes neck rot to bulbs and attacks stems and
  umbels of seed stalks
• WHITE ROT fungus (Sclerotium cepivorum,
  Sclerotinia sclerotiorum)
• Orange Alert
• Doesnt actually travel on seed, but black
  sclerotia can easily get mixed with seed because
  they look so similar
• Most prevalent in cool seasons and poorly-drained
  fields
• Sclerotia can persist in soil for up to fifteen
  years

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White Rot Symptoms
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White Rot Symptoms
Fluffy white mold, black spores and sclerotia
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Onion Disease Control

• Watch out for sclerotia in incoming seed
• Avoid overhead irrigation
• Avoid working in wet fields
• Scout for mold throughout season
• Do not allow any infected bulbs to go to seed.
  Once sclerotia are mixed with seed, theyre
  nearly impossible to separate completely

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TOMATO TOP SEED-BORNE DISEASES

• TOMATO MOSAIC VIRUS (TMV)(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
• BACTERIAL DISEASES (Bacterial canker
  (Corynebacterium michiganense pv. michiganense),
  Bacterial Spot (Xanthomonas campesiris pv,
  vesicatoria), Bacterial Speck (Pseudomonas
  syringae pv. tomato)- Orange Alert- Highly to
  moderately virulent, highly seed-borne- Cause
  considerable damage, but eradicated from seed by
  fermentation and/or hot water treatment

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Tomato Mosaic Virus symptoms
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Bacterial Canker Symptoms
Round, pale, birdseye spots
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Bacterial Spot Symptoms
Scabby, raised spots. Infects green fruit.
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Bacterial Speck Symptoms
Spots smaller, more shallow
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Tomato Disease Control

• For TMV, use strip tests to assay seed
• If TMV appears, destroy plants
• For bacterial diseases, heat-treat seed ahead of
  time
• Ferment all seed during harvest

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What is a growers 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

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What are the scenarios when I find ANY kind of
disease in a seed crop?
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(No Transcript)
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I. If its not a seed-borne disease, treatment
would be applied to keep the plants alive to make
seed
E.g. common leaf-spot diseases such as early
blight
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II. If its a disease of low to moderate
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
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III. For most seed-borne diseases, the crop is
typically destroyed if the disease is present
This avoids spending any more time or money on a
crop that wont make saleable seed
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SEED TREATMENTS FOR DISEASE ERADICATION

• Hot Water
• Bleach
• Experimental treatments

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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
• Cant be done as easily during harvest, so often
  requires wetting and re-drying seed

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Hot Water Requirements

• 42-50C (118-122F)
• 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 lab-grade water bath incubator
  (150-800 on ebay)

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Shaking Water bath
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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
  cant 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

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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

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Other Treatments

• Natural II
• Biocontrol agents, e.g.

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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.

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Online Resources

• Common Names of Plant Diseases
• http//www.apsnet.org/online/common/toc.asp
• Cornell Universitys Plant Disease Diagnostic
  Clinic Homepage http//plantclinic.cornell.edu/
  Default.htm
• Simplified Fungi Identification Key
• http//www.plant.uga.edu/Extension/pubs/fungikey.p
  df
• SBML Fungal Databases Selecting Fungus-Host
  Distributions
• http//nt.ars-grin.gov/fungaldatabases/fungushost/
  fungushostframe.cfm
• Vegetable Diseases Fact Sheets listed by Crop
• http//vegetablemdonline.ppath.cornell.edu/cropind
  ex.htm
• Plant diseases directory for agricultural crops
  Manitoba agriculture, food, and rural initiatives
• http//www.gov.mb.ca/agriculture/crops/diseases/in
  dex.html
• Plant Disease Information System
• http//www.pdis.org/
• 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 http//ohioline.osu.edu
  /hyg-fact/3000/pdf/3086.pdf (verified 10 March
  2010).

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